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Efik Origin Story Compiled by David Baker, adapted by Newsela In this origin story of the Nigerian Efik people, the first humans defy the gods to achieve greater power and wisdom. The Efik people live in southern Nigeria, for many centuries dwelling near the regions around the Cross River. They traditionally worshipped the god Abassi as a supreme creator. Their belief system was very relaxed. They had no formal priesthood or organized religious institutions. Worship and ritual were carried out on an individual or family level. Their creation story is a tale of humans defying the gods in order to achieve greater power and wisdom. Before Abassi there was nothing. Abassi was god of the Universe, and giver of life, death, and justice. He was so powerful that he could create life, heal the sick, and even raise the dead. Some say that Abassi was the Sun, and they worshipped it as it rose and set every day. Abassi lived in the sky with his wife, Atai. She was a wise goddess, who often gave Abassi good advice. Abassi created the stars, the Earth, and all the wildlife upon it. He also created two humans, a man and a woman. These humans lived with Abassi and Atai in the sky. They were very innocent and had little knowledge. Abassi and Atai looked after them, protected them, and even fed them, because they did not know how to feed themselves. One day, the humans were looking down from the sky at the Earth. They decided they wanted to live there. But when they asked Abassi if they could leave the sky and live on the Earth, he forbade it. The Earth was a place with many secrets where many things could be learned. Abassi feared that the humans would one day match his wisdom, or even surpass it. Atai proposed a compromise. The humans could go live on Earth, but they had to return to the sky every day to have their meals. The humans were forbidden to learn to hunt or farm. They were also forbidden to marry and have children, because a large nation of people might one day challenge the power of Abassi. For a while, this plan worked. The humans returned to the sky every day to take their meals. However, one day, the woman decided she was sick of being fed like a helpless child. She went out into the fields and began to farm. When the time came for dinner, she defiantly refused to return to the sky with the man. The next day, the man visited the woman in the fields and saw she was growing her own food. He decided to help her. Before long, the man and woman fell in love. They did not return to the sky again. Many years went by and they had many children. When those children were old enough, they joined their parents working in the field. They all continued to learn the secrets of the Earth and teach them to each other. The humans tried to hide their children from the sight of Abassi, but the god saw them. He grew very angry. He blamed his wife, Atai, because she had convinced him to let the humans live on Earth. Abassi feared that one day, the humans would have learned so much that they would surpass his wisdom. He also feared they would grow so numerous that they would surpass his power But Atai had a plan. In order to prevent the humans from growing too powerful, she sent evil into the world in the form of death and discord. The evil was so strong that the man and woman immediately died. Their children have suffered the ills of the world and argued among themselves ever since. But because their mother defied the gods, the humans have continued to learn the secrets of the Earth. For Further Discussion Now that you’ve read all of the origin stories, see how your Origin Stories Chart answers compare to those on the answer key.  Did we miss anything? If so, share what we missed in the Answers Area below. Sources Beier, Ulli. The Origin of Life and Death: African Creation Myths. London: Heinemann, 1966. Hackett, Rosalind. Religion in Calabar: The Religious Life and History of a Nigerian Town. Berlin: Mouton de Gruyter, 1988. Leeming, David Adams. Creation Myths of the World: An Encyclopedia. 2nd ed. Santa Barbara: ABC-CLIO, 2010. Lynch, Patricia Ann, and Jeremy Roberts. African Mythology: A to Z. 2nd ed. New York: Chelsea House, 2010. Image Credits Landscape with Stars by Henri-Edmond Cross © Corbis

What Happened on Easter Island? By David Burzillo, adapted by Newsela Easter Island is most famous for moai, the huge statues that encircle the island. What caused its civilization to collapse? Introduction In the spring of 1722, Dutch explorers landed on Easter Island. Upon arrival, they found a most puzzling and fascinating sight – hundreds of massive stone statues were all over this tiny island. What are they? What do they mean? Why are they placed where they are? How did they get there? The huge stone figures of Easter Island have fascinated explorers, researchers, and just about anyone who has seen them for hundreds of years. In spite of many years of research, scholars still don’t agree on the answers to the puzzle of the statues. Even more intriguing, perhaps, are the questions surrounding the rise and fall of the population that built them. Easter Island, which native Polynesians call Rapa Nui, is located in the eastern Pacific Ocean. Today it is part of Chile, where it is called Isla de Pascua. The island is more than 2,000 miles from nearly all its neighbors. Easter Island is 700,000 years old, which is fairly young for an island. It was formed by volcanic activity, and now its landscape is dominated by three dormant volcanoes. The island is very small—around 60 square miles. This makes it less than one tenth the size the Hawaiian island of Maui, or just about the size of Gainesville, Florida. Location of Easter Island in the southeastern Pacific Ocean Scholars do not agree on when people first settled on Easter Island. The first arrived by boat sometime between 300 and 800 CE. These settlers probably rowed there from a Polynesian island about 4,000 miles away. They brought bananas, taro, sugarcane, chickens, and rats with them, adding to the natural life already on the island. Today, Easter Island is home to over 7,600 people1^11start superscript, 1, end superscript and attracts over 100,000 tourists a year2^22squared. Why is Easter Island so fascinating? For such a small piece of land, Easter Island has been given a lot of attention for a long time. One source of this interest is the beauty of the island and its potential for supporting life. The Dutch ship captain Jacob Roggeveen wrote the following description of the island in 1722: Nor can the aforementioned land be termed sandy, because we found it not only not sandy but on the contrary exceedingly fruitful, producing bananas, potatoes, sugarcane of remarkable thickness, and many other kinds of the fruits of the earth; although destitute of [lacking] large trees and domestic animals, except poultry. This place, as far as its rich soil and good climate are concerned, is such that it might be made into an earthly Paradise…..3^33cubed Satellite image of Easter Island, Earth Observatory, NASA, public domain. But by far, Easter Island is most famous for the moai. The moai (pronounced moe-eye or mah-eye) are huge statues that encircle the island. Moai at Rano Raraku, Easter Island, by Aurbina, Public Domain. These enormous statues of elongated faces are so popular there is even a moai emoji. There are between 887 and 1,000 moai on Easter Island. The largest are 33 feet high and weigh as much as 80 tons. Most of them are located miles from the quarries that provided the stone for them. The size, number, and location of the moai raise a number of questions that scholars have puzzled over for many years. How did the people carve these statues without metal tools? How did they move them without the help of large animals? What purpose did they serve for the islanders? Detailed topographic map in Spanish of Easter island, by Eric Gaba, translation Osmar Valdebenito, CC BY-SA 2.5 Anthropologists, archaeologists, and historians have been digging for clues about this fascinating place for many years, but there are no simple answers. Terry Hunt and Carl Lipo, both experts in anthropology and archaeology, took on these tough questions. In 2011, they published an article that re-created how the Easter Islanders may have been able to move the statues. Then, in January 2019, a research team including Hunt and Lipo published another article explaining the location of the statues. They suggested that the moai may have been placed in areas where fresh or brackish water was found, as a way of marking the location of this important resource.4^44start superscript, 4, end superscript Exciting answers (or at least theories) are still being published, and the many questions about Easter Island will probably continue to inspire research across many disciplines. In recent years, researchers have also begun to ask questions about the history of environmental change and population decline on the island. These changes are represented in the following two charts. What were the causes of the changes represented in these graphs? How could such changes have happened to an island with such an isolated but advanced society? As they’ve explored these questions, historians, archaeologists, and botanists have uncovered evidence. Some of this evidence is in the form of written documents. Some is in the form of artifacts and other material remains. Historians have studied the accounts of the first European visitors to the island. These impressions that people wrote when they first came ashore to this new and intriguing place provide information about what the island was like hundreds of years ago. Archaeologists have uncovered artifacts and excavated the remains of buildings from ancient settlements. A variety of scientists have studied the plants, animals, and geology of the island. Easter Islanders did have a form of writing, called rongorongo, but scholars have not yet discovered a way to read this writing. Easter Islanders may have written about the challenges they faced, but we may never know what they thought. How have scholars explained the environmental and population changes on Easter Island? Some scholars place the blame for changes on the island on humans. Geographer Jared Diamond illustrates this somewhat controversial opinion: In short, the reason for Easter’s unusually severe degree of deforestation isn’t that those seemingly nice people really were unusually bad or improvident [careless]. Instead, they had the misfortune to be living in one of the most fragile environments, at the highest risk for deforestation, of any Pacific people…. Easter’s isolation makes it the clearest example of a society that destroyed itself by overexploiting [overusing] its own resources.5^55start superscript, 5, end superscript Many of the explanations that blame humans for these problems have focused on the issue of the overuse of the resources available on Easter Island. Deforestation (removal of trees) is the primary cause in these explanations. Easter Islanders cut down trees for a variety of purposes. Trees were probably used to move the moai. Trees also provided the materials for making rope. People also used trees for fuel. Terry Hunt, the anthropologist/archaeologist mentioned earlier, has found that “Between 1300 and 1650…inhabitants burned wood from trees, but they used grass, ferns and other similar plants for fuel after that point.”6^66start superscript, 6, end superscript This tells us that deforestation was underway by the time Europeans arrived. Some researchers argue that trees were cut down using a method known as “slash and burn” to create more farmland. One research team found “a single layer of charcoal and ashes several millimeters in thickness can be found deep below the recent surface…. The extensive distribution of charcoal layers can only have one explanation: widespread fires in the woodland of Rapa Nui…. the beginning of intensive slash and burn….”7^77start superscript, 7, end superscript Other experts have focused more on the role of environmental factors in the changes on Easter Island. Some of these researchers, including Hunt and Lipo, have focused on the island’s large rat population. Rats did not have many competitors and their population could grow rapidly. Rats were big consumers of palm nuts, the seeds for growing trees on Easter Island. Hunt and Lipo write, “It takes several years for the tree to form a trunk and sixty or more years to produce seeds. With rats consuming so many of the palm nuts, as the record suggests, few trees could regrow naturally.”8^88start superscript, 8, end superscript Many researchers have focused on the impact of diseases brought by European visitors to the island. Because Easter Island is so remote, it had very little contact with other human communities for hundreds of years. The people there developed no immunity to the diseases brought by Europeans. As a result, sickness would have spread quickly. Hunt and Lipo point out that the Europeans were probably unaware of the enormous effect disease would have had on the island’s population. They write that Captain Cook and his men, who visited the island around 1770, “were perplexed by the small population size, what they perceived as poverty, and generally the disheveled [messy] state of things; in hindsight, this is precisely what the aftermath of an epidemic and population crash would look like.”9^99start superscript, 9, end superscript Conclusion Scholars from many disciplines continue to study Easter Island in an attempt to understand how it changed over the centuries, and in particular how humans were affected by or caused these changes. The moai are a stunning visual reminder of the deeper mysteries that surround the island and its inhabitants. Perhaps those statues are the perfect guarantee that scholars will continue trying to understand how and why the population of this remote corner of the world developed as it did. All 15 standing moai at Ahu Tongariki, excavated and restored in the 1990s, by Bjørn Christian Tørrissen, CC BY-SA 3.0. [Notes] [Sources and attributions]

Big History: An Overview By John Green, adapted by Newsela History is an attempt to understand both our insignificance and our significance. To study history is to better understand the world and your place in it. You are very small. You are one of several billion living members of your species, a species that lives on the fifth largest planet orbiting a star we call the Sun. There are more than a hundred billion such stars in our galaxy, and perhaps a hundred billion galaxies in the Universe. It’s almost impossible to grasp your smallness—there are more stars in the Universe than there are grains of sand on Earth. And yet, you’re also very large. You’re a member of an extraordinarily powerful species that has dramatically reshaped the biosphere, the first species on Earth to understand the vastness of the Universe around it. Your choices—how to organize your community, what to value, what to battle against—shape not just your life but the lives of those around you and the lives of those still to come. And you are physically vast as well: Your body contains trillions of cells, and is colonized by trillions more microscopic organisms. What Is History? History is an attempt to understand both our insignificance and our significance. To study history is to better understand the world and your place in it. You, and the other humans with whom you share this world, are the culmination of the human story. What Is Big History? There’s a lot more to history than the human story. Let’s consider the world before humans. If you think of history as the story of life on Earth, almost all of it played out before our species (Homo sapiens) showed up on the scene. After all, we’ve been around only for the last 250,000 or so years—less than 0.01% of the history of life on Earth. From the very beginning, we’ve had different stories that explain the origins of the Universe, our planet Earth, and life itself. These origin stories, as they’re called, are as varied as the cultures that created them. At its heart, Big History is simply another origin story. However, it differs from all other origin stories because it’s science based. Big History uses the information we have available—the scientific evidence—to create an understanding of the Universe. Thresholds of Increasing Complexity Because the scale of Big History is so vast (remember, it covers the history of the Universe), it would be impossible for this story to include everything. All historians have to make choices about what to include and what to leave out in the stories they tell. So, what does the story of Big History focus on? Big Historians focus on eight turning points in the history of the Universe, which we call thresholds. These are moments when the Universe became significantly more complex than it had been previously. Threshold 1: The Big Bang Modern science suggests that the Universe was created in a “big bang” about 13.8 billion years ago. The Big Bang was a split second in which all matter and energy expanded at tremendous speed and became the Universe. What was there before the Big Bang? It’s mind-bending to think about, but in some ways, there was no “before” the Big Bang, because the Big Bang created not only space as we know it, but also time as we know it. The important thing to know is that around 13.8 billion years ago, very suddenly, the Universe exploded into being. It’s also important to recognize that although scientists know a lot about the Big Bang, there are still many questions about the details that are being researched. Threshold 2: The Stars Light Up After the Big Bang, the Universe expanded and cooled. It took some time (about 380,000 years), but eventually it was cool enough for the simplest atoms, hydrogen and helium, to form. The early Universe consisted almost entirely of hydrogen and helium for a very long time. After a few hundred million years, clouds of hydrogen and helium began to collapse, and the increasing heat and pressure generated by collapse led to the creation of the first stars. Stars represent the second threshold of increasing complexity in Big History. Not only are stars more complex than simple atoms, they’re also able to create tremendous energy. Over time, gravity grouped stars into galaxies, which created further complexity in the Universe. Threshold 3: New Chemical Elements Stars made the Universe more complex, but the Universe still consisted primarily of hydrogen and helium. This changed when the first generation of stars died. The death of a star can generate high temperatures and pressures like those in the Big Bang, and this makes possible the creation of more complex atoms. A greater variety of atoms is critical to making more complex things like planets and living things, so the death of stars is the third threshold of increasing complexity in Big History. Threshold 4: Earth and the Solar System Our Sun is a star, and like all other stars, it was formed from the collapse of a huge cloud of gas and dust particles. More than 99 percent of this material went to make up the Sun, but wisps of matter orbited around it at various distances. Over time, the matter in each orbit was drawn together by gravity. The gravitational pull created violent collisions into lumps of matter that eventually formed the planets. This process, which we call accretion, is how our Earth was formed approximately 4.5 billion years ago. Threshold 5: Life Around volcanic vents at the bottom of Earth’s oceans, complex chemicals engaged in ever-changing reactions powered by the heat from these volcanoes. Those reactions led to the formation of complex chemicals that eventually created the first living organisms. The earliest living organisms consisted of single cells, as most living organisms do even today. Like all living organisms, those early single-celled creatures were subject to the laws of evolution. Generation by generation, the average features of species gradually changed, eventually forming entirely new species. And for a very long time, that was it: single-celled, microscopic organisms. Life first emerged on Earth perhaps three billion years ago; the first multicellular life didn’t show up until around one billion years ago. But slowly, life grew more and more complex, and large, multi-cellular organisms eventually spread, not only in water, but also on land. One hundred million years ago, the land-based animals that flourished most were the reptiles we call dinosaurs. About 65 million years ago, however, most of them died off. Now other types of large animals could flourish in their place. Most successful of all in the last 65 million years has been the large class of animals called mammals. Threshold 6: Collective Learning The extinction of the dinosaurs allowed mammals and primates to evolve and eventually dominate the Earth. Our ancestors, the hominins, are primates, and they first appeared between five and seven million years ago in Africa. Over millions of years, hominins evolved in important ways, both physically and socially. About 200,000 years ago, Homo sapiens, which means “wise human,” appeared. Modern humans developed language, a method of communication that allows them to share complex ideas and pass on knowledge from generation to generation. This process is known as collective learning. In other species, knowledge dies with the generation that created it. Humans have the ability to build on the accomplishments of previous generations. Threshold 7: Agriculture Our ancestors lived by foraging. Foragers survive by gathering plants, hunting animals, and scavenging the remains of animals killed by other predators. Foraging supported early humans for millions of years. About 12,000 years ago, humans began to domesticate plants and animals, in other words, to farm. They began interfering with the natural life cycles of plants and animals in order to control where they grew and promote characteristics in those plants and animals they preferred. Growing food gave humans access to a vast amount of energy created by the Sun through photosynthesis. Because foraging for survival was no longer necessary, tremendous lifestyle changes were possible, like settling down to live in cities, creating political structures, and developing skill and trade specializations. The results of all of these changes define the agrarian civilizations. Farming has had a tremendous impact on the way humans live and how they interact with the Earth. Threshold 8: Modern Revolution The adoption of farming led to dramatic changes in the way humans lived. Innovation accelerated dramatically with the Modern Revolution, which began about 300 years ago. Rapid growth of human population and the creation of a highly interconnected world are some of the key features of the modern world. These features make the modern world the eighth and final of Big History’s thresholds. What's Next? The story of the Universe isn’t only about the past. We know that this story doesn’t end with Threshold 8. So, what’s next? What might the next threshold of increasing complexity be? When you reach the end of this course, you’ll get to use your knowledge of the past to speculate about the future. Because Big History isn’t just about knowing what happened when. Big Historians look across the thresholds to understand the connections between past and present. With that understanding, developing a view of what the future might hold becomes more than a random guessing game. It becomes a way of expressing your own point of view about how the future will be the logical outcome of billions of years of the past. But let’s not get ahead of ourselves. Let’s really dig into the vastness of what got us here. Remember, you are very small, yet very large. In any other story, this might seem like a contradiction—but not here, not in the Big History story!

Zulu Origin Story Compiled by David Baker, adapted by Newsela Different versions of the Zulu origin story all share this theme: Life has a single common ancestor. The Zulu are a proud African people, famous throughout history for their fierceness and bravery in fending off invaders. Archaeologists tell us they traveled to the lush green lands of south-eastern Africa many centuries ago from the huge lake regions to the north. Their creation story has many versions, passed down by word of mouth from generation to generation. It tells of how the ancestors of all plants, animals, and humanity began from a single source At first, there was nothing but darkness. Earth was a lifeless rock. But in that darkness dwelt a god, Umvelinqangi, whose voice was like thunder and who, when angered, would shake the world with earthquakes. Umvelinqangi created a single tiny seed. He sent it to the Earth. This seed was the very first life, from which all other life descended. It landed in the soil and sprouted into a long reed. The reed dropped more seeds, which fell off and grew into even more reeds. This continued until they covered a massive swamp to the north, the land called Uthlanga. At the end of one reed, there grew a man. His name was Unkulunkulu, known as “the first ancestor” and “the Great One.” Very small at first, he grew so large and heavy that he snapped off the end of the reed. Walking across the land of Uthlanga, he noticed men and women were sprouting at the ends of the other reeds. He picked them from the reeds. These people were the first humans, the ancestors of all nations, and they spread across the Earth. It was from Uthlanga that the ancestors of the Zulu journeyed south to the fertile lands they inhabit today. The Great One continued to walk among the reeds. He saw many forms of life growing at the end of them. He gathered the fish and flung them into the rivers. Fields and forests began to grow, so he harvested birds and antelope, and they darted off into the wild. He picked cattle so they could be used by humans. He plucked off a ball of fire and a round glowing stone, and flung them into the sky. These were the Sun and Moon. Light came into the world. The Great One also plucked from the reeds fierce lions and other beasts that would travel the lands hunting prey. He harvested magical creatures, some good and some bad. One was the snake-like goddess of the rivers, Mamlambo, rumored by some Zulu to drown people, eat their faces, and suck out their brains. Another goddess was Mbaba Mwana Waresa, a beautiful woman who created rain and rainbows, and who invented farming and gave the Zulu the gift of beer. One of the final acts of the Great One was the most tragic. He plucked the first chameleon off a reed and sent it to give humans the following message: “Men must not die.” By the words of the Great One, humans would become immortal. Unfortunately, the chameleon was slow and lazy in his journey. The Great One grew impatient and picked a different lizard from a reed. This lizard was fast and quickly arrived to give word to the humans. But the lizard did not bear the same instructions. Instead the lizard uttered the words, “Men must die.” And so from that day, humans became mortal. It is said that chameleons change color because they are so ashamed their ancestor was not fast enough to spare humankind the invention of death. Sources Leeming, David Adams. Creation Myths of the World: An Encyclopedia. 2nd ed. Santa Barbara: ABC-CLIO, 2010. Lynch, Patricia Ann, and Jeremy Roberts. African Mythology: A to Z. 2nd ed. New York: Chelsea House, 2010. Image Credits Zulu Huts on Film Set KwaZulu Natal, South Africa © Corbis

All of the following terms appear in this unit. The terms are arranged here in alphabetical order. adapt — Make fit for, or change to suit a new purpose; adapt or conform oneself to new or different conditions ancestor — Someone from whom you are descended (but usually more remote than a grandparent) astrophysics — The study of the properties and interactions of planets, stars, galaxies, and other astronomical objects. Big Bang — A theory, first articulated in the 1920s, proposing that the Universe started out extremely hot and dense and gradually cooled off as it expanded. Big History — A unified account of the entire history of the Universe that uses evidence and ideas from many disciplines to create a broad context for understanding humanity; a modern scientific origin story. century — A period of 100 years challenge — Issue a challenge to; a demanding or stimulating situation; a call to engage in a contest or fight; questioning a statement and demanding an explanation complexity — A quality of an object or system that has diverse components precisely arranged in connection with one another (so that new properties emerge which did not exist in the components alone). cosmology — The study of the Universe on its largest scales, including its origin. creation — The even that occurred at the beginning of something; the act of starting something for the first time; the human act of creating; (theology) God's act of bringing the Universe into existence; everything that exists anywhere creature — A living organism characterized by voluntary movement; emergent properties — Properties of a complex system that are not present within its parts but that emerge only when those parts are combined. entropy (the law of) — The natural tendency of all things to move from order to disorder. (Note: Although often called the law of entropy, it is more accurate to refer to it as the second law of thermodynamics.) goddess — A female deity Goldilocks Conditions — Specific set of conditions necessary to enable greater complexity. The reference is to the fairy tale Goldilocks and the Three Bears, in which Goldilocks looks for the porridge, chair, and bed that are “just right.” history — The study of past events. human — Relating to a person; having human form or attributes as opposed to those of animals or divine beings; any living or extinct member of the family Hominidae characterized by superior intelligence, articulate speech, and erect carriage; characteristic of humanity ingredients — Components that are put together to form something new and more complex. interdisciplinary approach — An approach to a subject that uses the viewpoints of many different kinds of scholars about the same topic. For instance, Big History relies on information from cosmologists, astrophysicists, geologists, chemists, paleontologists, biologists, anthropologists, and historians, as well as experts in other disciplines, to learn about the past. origin story — A narrative about the beginning of the Universe and humanity. religion — A set of beliefs and practices that concern humanity’s relationship with the spiritual, the supernatural, and reality. scale — Degrees of magnification, or perspective, used to measure time, space, and size. science — An approach to discovering knowledge about the natural world that relies on testing ideas through observation or experiment. scientific notation — A method of expressing very large and very small numbers to avoid using the many zeros that would be required otherwise. thresholds of increasing complexity — Moments in the history of the Universe when specific ingredients under the right “Goldilocks Conditions” come together to create something new and more complex. Universe — All the matter and energy in existence, as well as the space that contains it. version — An interpretation of a matter from a particular viewpoint; something a little different from others of the same type

Cosmology and Faith An illustration of multiple worlds by 18th-‐century mathematician Leonhard Euler © Science Source By John F. Haught Since the beginning of human existence on our planet, people have asked questions of a religious nature. For example, what happens to the dead? Human beings have always wondered how things hang together. Our minds spontaneously look for connections, and we remain restless until we find them. Nothing is really intelligible unless we can relate it to other things. This is why science is such a satisfying adventure. Its mathematical principles tightly unify everything that goes on in the cosmos. Every occurrence, science tells us, is subject to the same fundamental physical laws everywhere. You can be sure, for example, that if you travel to another galaxy in our Big Bang Universe you will find the same laws of physics and chemistry operative there as on Earth. Although the Universe unfolds in rich diversity, it rests upon an underlying physical and mathematical simplicity. Before modern science came along our ancestors were not aware of the physical universality that ties all of nature together. Nevertheless, our ancestors were just as interested in finding connections as we are. The main way in which they brought coherence to their experience of things and events was to tell stories about them. These stories often took the form of myths about cosmic, biological, and human origins. Understanding the origin of things apparently reduces human anxiety in the face of the unknown. We still need stories. Big history is a good example of the human longing for narrative coherence. We want to understand, for example, how life is tied into physical processes and how the history of human beings on Earth is bonded to the natural world that gave birth to us. Science now allows us to tell a whole new story about our connection to nature. Remarkably, over the last two centuries the natural sciences have increasingly demonstrated that the Universe itself has a history and that human life is a relatively new chapter in the cosmic story. We did not float in from some other world. We blossomed gradually from roots that extend all the way back to the Big Bang. It is enormously satisfying now to be able to tell the story of the emergence of atoms, stars, planets, cells, organisms, and minds. A 1784 diagram of the Milky Way by astronomer William Herschel. © Science Source What about religion? Science and history both try to understand how things hang together, but religions do too. Since the beginning of human existence on our planet, most people have asked questions of a religious nature. For example, what happens to the dead? Are they somehow still connected to the world of the living? In his insightful book The Broken Connection, psychiatrist Robert Jay Lifton observes that in the scientific age the bonds our ancestors felt between the living and dead have been weakened or completely broken. Scientifically educated people now often question the connection that religions professed to find between our present life and a wider world of sacred mystery. Nevertheless, many of us still ask religious questions. Why, for example, does anything exist at all? Why do living beings suffer? What happens when we die? Why do human beings have a sense of rightness and wrongness? How can we find a meaning for our lives? Can we ever find final release from concerns over sickness, oppression, isolation, and guilt? Where can we find perfection? What is really going on in the Universe? Responses to these religious questions have usually taken the form of myths and other kinds of narratives. To most religions the “really real” world is infinitely larger than the visible one available to scientific study. Religions try to connect people to this wider world. Ever since the earliest stories and oral traditions, most people have had an intuition that the world is large enough to include spirits, gods, and long-departed ancestors. Religions strive to break through the physical limits that cut human existence off from the mysterious worlds to which their symbols and stories point. Religions seek to mend the sense of broken connection that stems from the experience of meaninglessness, guilt, pain, and death. Major religious traditions such as Buddhism, Hinduism, Judaism, Christianity, and Islam still hold out the hope of salvation from everything that hems us in or holds us down, including the fact that everything eventually perishes. It is therefore not hard to understand why religions have been so important to most people throughout history and around the globe. Each of Earth’s main religious traditions has countless tributaries and off-shoots. Religion on Earth is so complex and diverse that it almost resembles a rain forest. Since religions are so central to the history of human existence on our planet, they rightly attract the interest of natural scientists and not just of historians and theologians. Any objective survey of big history, therefore, cannot ignore the dominant role that religions have played in shaping the consciousness of most people who have ever lived. The question of science and faith In the age of science, however, what are we to make of religions and their sense of a connection between our present existence and a larger, scientifically unavailable life-world? Hasn’t science made religious symbols, narratives, and teachings unbelievable? For the sake of simplicity, as we address these questions let us refer to the whole body of religious hopes, stories, doctrines, speculation, prayers, and rituals as “faith.” More fascinating questions arise for your consideration: Can human minds shaped by faith traditions that stem from a prescientific era honestly take modern science seriously? Or, if you develop a sense of big history, can you still honestly accept the teachings of your faith tradition if you have one? Does belief in God, for example, contradict science, as many educated people now maintain? Isn’t it hard to be both a serious scientist and a person of faith? Or is there a way of making a plausible con- nection between science and faith? Even though it is not my task to answer such questions, it is appropriate at least to take note of their existence, especially since humans and their religious instincts are as much a part of nature as rocks and rivers. What does it say about the Universe that it has recently given birth to conscious beings who want to connect their lives to worlds that science cannot see? Many scientists, philosophers, and other skeptics wish that religious faith would just go away so that only science would remain to fill our minds and aspirations. Others, however, think that scientific discoveries, including our new sense of cosmic history, still raise questions that science alone is powerless to address. For example, why does the Universe exist in the first place? Is anything of lasting significance working itself out in the 14-billion-year-old cosmic story? Is there any point to it all? What are we supposed to be doing with our lives if we are a part of a Universe that is still coming into being? Is there any solid reason for hope in the future? There are at least three main ways of responding to questions that science raises for people of faith: Shape your own answers, make your own connections, and find your own way of understanding the beginning and how things “hang together.” For most people these are questions that will not just slip quietly away. For Further Discussion Think about the conflict, contrast, and convergence ideas that were presented in the Haught article—what do you think makes the most sense and how can you logically argue for your side? In the Questions Area below, post the side that makes the most sense and provide two reasons that support your choice. Author Bio John F. Haught is a Roman Catholic theologian and senior research fellow at the Woodstock Theological Center at Georgetown University, in Washington, D.C. He established the Georgetown Center for the Study of Science and Religion and is the author of numerous books, including Science and Faith: A New Introduction (Mahwah, NJ: Paulist Press, 2012). Image Credits An illustration of multiple worlds by 18th-century mathematician Leonhard Euler© Science Source A 1784 diagram of the Milky Way by William Herschel© Science Source Young Buddhist monks praying© Scott Stulberg/CORBIS

Greek Origin Story: The Titans and the Gods of Olympus An illustration of Zeus crowned by Victory © Bettmann/CORBIS Compiled by Cynthia Stokes Brown This origin story comes from some of the earliest Greek writings that have survived. We know the Greek origin story from some of the earliest Greek literary sources that have survived, namely The Theogony and Works and Days, by Hesiod. This oral poet is thought to have been active sometime between 750 and 650 BCE, within decades of when the Homeric epics, The Iliad and The Odyssey, took the form in which we know them. Archeological findings support the creation story recorded in Hesiod’s work; pottery from the eighth century BCE depicts the gods and goddesses he describes. Before Hesiod told this patriarchal version, in which the first woman is the cause of much trouble, Pandora, whose name means “gift giver,” was known in oral tradition as a beneficent Earth goddess. In the beginning there was Chaos, a yawning nothingness. Out of the void emerged Gaia (the Earth) and other divine beings — Eros (love), the Abyss (part of the underworld), and the Erebus (the unknowable place where death dwells). Without male assistance, Gaia gave birth to Uranus (the Sky), who then fertilized her. From that union the first Titans were born — six males: Coeus, Crius, Cronus, Hyperion, Iapetus, and Oceanus, and six females: Mnemosyne, Phoebe, Rhea, Theia, Themis, and Tethys. After Cronus (time) was born, Gaia and Uranus decreed no more Titans were to be born. Cronus castrated his father and threw the severed genitals into the sea, from which arose Aphrodite, goddess of love, beauty and sexuality. Cronus became the ruler of the gods with his sister-wife, Rhea, as his consort. The other Titans became his court. Because Cronus had betrayed his father, he feared that his offspring would do the same. So each time Rhea gave birth, Cronus snatched up the child and ate it. Rhea hated this and tricked him by hiding one child, Zeus, and wrapping a stone in a baby’s blanket so that Cronus ate the stone instead of the baby. When Zeus was grown, he fed his father a drugged drink, which caused Cronus to vomit, throwing up Rhea’s other children and the stone. Zeus then challenged Cronus to war for the kingship of the gods. At last Zeus and his siblings, the Olympians, were victorious, and the Titans were hurled down to imprisonment in the Abyss. Zeus was plagued by the same concern as his father had been and, after a prophecy that his first wife, Metis, would give birth to a god greater than he, he swallowed Metis. But she was already pregnant with Athena, and they both made him miserable until Athena, the goddess of wisdom, civilization and justice, burst from his head — fully grown and dressed for war. Zeus was able to fight off all challenges to his power and to remain the ruler of Mt. Olympus, the home of the gods. One son of Titans, Prometheus, did not fight with fellow Titans against Zeus and was spared imprisonment; he was given the task of creating man. Prometheus shaped man out of mud, and Athena breathed life into the clay figure. Prometheus made man stand upright as the gods did and gave him fire. Prometheus tricked Zeus, and to punish him, Zeus created Pandora, the first woman, of stunning beauty, wealth, and a deceptive heart and lying tongue. He also gave Pandora a box she was commanded never to open, but eventually her curiosity got the best of her, and she opened the box to release all kinds of evil, plagues, sorrows, and misfortunes, and also hope, which lay at the bottom of the box. For Further Discussion Which two origin stories are the most similar and which are the most different? Explain your answer in the Questions Area below. Sources www.greekmythology.com David Leeming and Margaret Leeming, A Dictionary of Creation Myths (New York and Oxford: Oxford University Press, 1994), 221. Image Credits

Approaches to Knowledge By Bob Bain, adapted by Newsela How do people create knowledge? It starts by being puzzled, curious, or even confused about the world. There’s a sense of wonder in it all. Here in a library, surrounded by books, I’ve set out to write about knowledge. Libraries make such appropriate places to discuss knowledge because their purpose is to store knowledge — that’s why communities build them. In many ways, libraries are repositories of collective learning, an idea that is very important in the Big History course. In this library and others, knowledge exists in many forms: books, maps, films, videos, CDs, and, of course, textbooks. The Big History class does not have a textbook, but it’s still useful to think about them and the knowledge within. I’ll tell you how I approached textbooks when I was a student and how most of my high school and college students approach their textbooks. They typically ask one big question: “How do we get the stuff out of that textbook and into our heads or, more important, onto the tests?” And frankly, that was the question I asked as a student: “How can I get the facts out of the textbook and onto the test?" Main Reading Room at the U.S. Library of Congress, courtesy of Carol McKinney Highsmith Archive, The Library of Congress Big History asks questions about knowledge In Big History we ask a very different question: “How did that knowledge get into the textbook?” That is, in Big History we wonder, “How did people discover the facts or create the ideas that are in our textbooks or in our courses?” Did you ever wonder how people create knowledge? Well, in this course you are going to meet many people who discovered or created the information that is in your textbooks. You will meet cosmologists, physicists, geologists, biologists, historians, and more. They are excited to tell you what they have learned. But they are also excited to tell you how they learned it. They are going to tell you how people in their field approach knowledge, the questions that interest them, and how they used intuition, authority, logic, and evidence to support their claims. In Big History, we want you to pay attention to the questions these scientists and scholars ask and the tools and evidence they use to answer their questions. Questions, tools, and evidence! Let’s look more carefully at how scholars use questions, tools, and evidence to create or discover ideas, facts, and knowledge. Most of the scholars you’ll meet in this course begin their investigations with questions. They are puzzled, curious, or even baffled about the world around them. Sometimes their inquiry begins in wonder. Unlike textbooks that place questions at the end of learning, scholars pose the questions first and use them to drive forward their learning. Galileo Explaining Moon Topography to Skeptics by Jean-Leon Huens © National Geographic Society/Corbis Have you noticed that your teacher, the Big History units, and David Christian’s videos all use questions — big questions — to launch your study? Before conducting an inquiry, scholars speculate or make a thoughtful guess about what they’ll learn. We often call these thoughtful guesses “conjectures” or “hypotheses.” But a question or a hypothesis isn’t knowledge yet. Scholars need to gather information to answer their questions. As you’ll learn in later units, sometimes people create or use new tools to help them gather new information. For example, Galileo used a telescope he made to collect new data about the heavens and the planets. Scholars turn information into evidence to support claims Gathering information does not automatically answer scholars’ questions. The information must also be organized, analyzed, and then evaluated to see if it answers the initial or driving questions. Scholars may then make claims that answer their questions, and use the information as evidence to support their claims. The stronger the evidence, the better the support for the claim — and the greater chance it has to enter a textbook, for others to learn about it. Scholars must show how they answered their questions Let’s review. In this essay, I wondered how knowledge gets in textbooks and, in answer to my question, I have described a few steps: First, scholars have questions or they are curious or puzzled about something.Second, they make a conjecture — a thoughtful guess or hypothesis.Next, they gather information to answer the question, often using new tools in the process.They then analyze the information, think about it, and, perhaps, use some of it to answer their question.Scholars use information as evidence to support or make their claims.When claims become well supported, they enter textbooks for students to learn. First, scholars have questions or they are curious or puzzled about something. Second, they make a conjecture — a thoughtful guess or hypothesis. Next, they gather information to answer the question, often using new tools in the process. They then analyze the information, think about it, and, perhaps, use some of it to answer their question. Scholars use information as evidence to support or make their claims. When claims become well supported, they enter textbooks for students to learn. But the scholars’ work is still not finished. They also must share what they learned and show how they learned it. Why do they have to show how they learned it? Isn’t simply telling what they learned enough? Why must they also explain how they conducted their investigation, how they analyzed their information, and how they supported their claims? Scholars want to contribute to collective learning. They want people to see how they arrived at their claims and what evidence supports the claims. They do not want people to simply trust their claims based only on intuition, logic, or authority. Scholars also want others to improve their claims. This might involve using new tools or new methods to gather new evidence to support or challenge the claims. Or it might mean asking a different question entirely. Different approaches to knowledge All the scholars you meet — whether archeologists, anthropologists, biologists, or experts in another field — ask important questions. They all make conjectures, gather data, and analyze it to make claims, but there are differences among and between these individuals. While they all ask important questions, make conjectures, gather data, and analyze it to make claims, there are differences among and between these scholars. They all begin their investigations asking questions, but they ask different questions. They all have ways to gather data, but they often have different ways to gather data. As you meet the instructors in this course, do more than just learn what they are teaching; try as well to understand how they do their work, what questions they ask, and how they answer their questions. You might ask each of them: What are the big questions that have interested you and driven you to personally pursue the answers?What were your guesses, speculations, and hypotheses?How did you collect your evidence?Where did you see the patterns in your evidence? What did those patterns seem to indicate?What were your biggest ideas?How did you make your ideas public?Why should others believe your ideas?When and why have you changed your mind? What are the big questions that have interested you and driven you to personally pursue the answers? What were your guesses, speculations, and hypotheses? How did you collect your evidence? Where did you see the patterns in your evidence? What did those patterns seem to indicate? What were your biggest ideas? How did you make your ideas public? Why should others believe your ideas? When and why have you changed your mind? Make sure to pay attention to big questions that haven’t been answered. These are questions that you and your friends might take up. Who knows? Maybe you can contribute to the textbooks of the future. Big History’s approach to knowledge As you might have already guessed, in Big History we ask lots of big questions. We’re going to ask questions about the physical world, the living world, and the human world. This will require us to use many different approaches to knowledge. One of the most exciting things about Big History is that we will use ideas that come from many different places. That is why you’re going to meet such a great variety of people who have contributed to our collective learning. And why we want to give you the chance to ask, “How did that knowledge get into the textbook?” For Further Discussion The ability to come up with good, researchable questions is something that we have learned that all scholars do, but how do they come up with those questions? What are some strategies you might use in figuring out how to ask the right questions when thinking about historical research and inquiry? Please share your strategies in the Questions Area below [Sources and attributions]

Judeo-Christian Origin Story: Genesis Compiled by Cynthia Stokes Brown This story comes from the first book of the Old Testament, the sacred source book of both Judaism and Christianity. This biblical story comes from Genesis, the first book of the Old Testament, which is the sacred sourcebook of both Judaism and Christianity. In Genesis this story is followed immediately by a second creation story, in which humans are created first, followed by plants and animals. These stories were written down in the first millennium BCE and evolved into the form in which we know them around 450 BCE, some 2460 years ago. Genesis: Chapter 1 In the beginning when God created the heavens and the earth, the earth was a formless void, and darkness was over the surface of the deep, and the Spirit of God was hovering over the waters. And God said, “Let there be light,” and there was light. God saw that the light was good, and he separated the light from the darkness. God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning — the first day. And God said, “Let there be a dome between the waters to separate water from water.” So God made the dome and separated the water under the dome from the water above it. And it was so. God called the dome “sky.” And there was evening, and there was morning — the second day. And God said, “Let the water under the sky be gathered to one place, and let dry ground appear.” And it was so. God called the dry ground “land,” and the gathered waters he called “seas.” And God saw that it was good. Then God said, “Let the land produce vegetation: seed-bearing plants and trees on the land that bear fruit with seed in it, of every kind.” And it was so. The land produced vegetation: plants bearing seed of every kind and trees bearing fruit with seed in it of every kind. And God saw that it was good. And there was evening, and there was morning — the third day. A detail from The Creation of the Sun, Moon, and Plants by Michelangelo Buonarroti © Bettmann/CORBIS And God said, “Let there be lights in the dome of the sky to separate the day from the night, and let them serve as signs to mark sacred times, and days and years, and let them be lights in the dome of the sky to give light on the earth.” And it was so. God made two great lights — the greater light to govern the day and the lesser light to govern the night. He also made the stars. God set them in the dome of the sky to give light on the earth, to govern the day and the night, and to separate light from darkness. And God saw that it was good. And there was evening, and there was morning — the fourth day. And God said, “Let the water teem with living creatures, and let birds fly above the earth across the dome of the sky.” So God created the great creatures of the sea and every living thing of every kind that moves in the teeming water, and every winged bird of every kind. And God saw that it was good. God blessed them and said, “Be fruitful and increase in number and fill the water in the seas, and let the birds increase on the earth.” And there was evening, and there was morning — the fifth day. And God said, “Let the land produce living creatures of every kind: the livestock, the creatures that move along the ground, and the wild animals, each of every kind.” And it was so. God made the wild animals of every kind, the livestock of every kind, and all the creatures that move along the ground of every kind. And God saw that it was good. And God said, “Let the water teem with living creatures, and let birds fly above the earth across the dome of the sky.” So God created the great creatures of the sea and every living thing of every kind that moves in the teeming water, and every winged bird of every kind. And God saw that it was good. God blessed them and said, “Be fruitful and increase in number and fill the water in the seas, and let the birds increase on the earth.” And there was evening, and there was morning — the fifth day. And God said, “Let the land produce living creatures of every kind: the livestock, the creatures that move along the ground, and the wild animals, each of every kind.” And it was so. God made the wild animals of every kind, the livestock of every kind, and all the creatures that move along the ground of every kind. And God saw that it was good. Then God said, “Let us make humankind in our image, in our likeness, so that they may rule over the fish in the sea and the birds in the sky, over the livestock and all the wild animals, and over all the creatures that move along the ground.” So God created humankind in his own image, in the image of God he created them; male and female he created them. God blessed them and said to them, “Be fruitful and increase in number; fill the earth and subdue it. Rule over the fish in the sea and the birds in the sky and over every living creature that moves on the ground.” Then God said, “I give you every seed-bearing plant on the face of the whole earth and every tree that has fruit with seed in it. They will be yours for food. And to all the beasts of the earth and all the birds in the sky and all the creatures that move along the ground — everything that has the breath of life in it — I give every green plant for food.” And it was so. God saw all that he had made, and it was very good. And there was evening, and there was morning — the sixth day. Thus the heaven and the earth were finished, with all their multitudes. And on the seventh day God rested from all the work that he had done in creation. God blessed the seventh day and hallowed it because on it God rested from all the work that he had done in creation.* For Further Discussion How is the Judeo-Christian origin story similar to the Greek origin story? How is it different? Share your answers in the Questions Area below. Sources New International Version, Genesis retrieved May 2011 from www.biblegateway.com Image Credits Detail of God from Creation of Adam by Michelangelo Buonarroti© Alinari Archives/CORBIS A detail from The Creation of the Sun, Moon, and Plantsby Michelangelo Buonarroti© Bettmann/CORBIS

Iroquois Origin Story: The Great Turtle Illustration of the Iroquois Prayer of Thanksgiving © National Geographic Society/CORBIS Compiled by Cynthia Stokes Brown The Iroquois people of North America spoke this story. Settlers from Europe wrote it down. This story comes from the Iroquois people in North America. In the 1400s they formed a federation of five separate tribes in what is now New York State. The Iroquois did not use writing, so they told this story orally until settlers from Europe wrote it down. The first people lived beyond the sky because there was no earth beneath. The chief’s daughter became ill, and no cure could be found. A wise old man told them to dig up a tree and lay the girl beside the hole. People began to dig, but as they did the tree fell right through the hole, dragging the girl with it. Below lay an endless sheet of water where two swans floated. As the swans looked up, they saw the sky break and a strange tree fall down into the water. Then they saw the girl fall after it. They swam to her and supported her, because she was too beautiful to allow her to drown. Then they swam to the Great Turtle, master of all the animals, who at once called a council. When all the animals had arrived, the Great Turtle told them that the appearance of a woman from the sky was a sign of good fortune. Since the tree had earth on its roots, he asked them to find where it had sunk and bring up some of the earth to put on his back, to make an island for the woman to live on. The swans led the animals to the place where the tree had fallen. First Otter, then Muskrat, and then Beaver dived. As each one came up from the great depths, he rolled over exhausted and died. Many other animals tried, but they experienced the same fate. At last the old lady Toad volunteered. She was under so long that the others thought she had been lost. But at last she came to the surface and before dying managed to spit out a mouthful of dirt on the back of the Great Turtle. It was magical earth and had the power of growth. As soon as it was as big as an island, the woman was set down on it. The two white swans circled it, while it continued to grow, until, at last, it became the world island as it is today, supported in the great waters on the back of the Turtle.* Engraving of a tattooed Iroquois © CORBIS For Further Discussion Writers often rely on origin stories to serve as the inspiration for books and films. Can you think of any examples of modern works that share elements of The Great Turtle? Sources Cottie Burland, North American Indian Mythology, Rev. ed. (New York: Peter Bedrick Books, 1985), 66. Image Credits

Origin Stories Introduction By Cynthia Stokes Brown All humans yearn to know where we came from and how our world began. We may have different stories, but they all serve a similar purpose. Everywhere around the world people tell stories about how the Universe began and how humans came into being. Scholars, namely anthropologists and ethnologists, call these tales “creation myths” or “origin stories.” In comic-book lingo there is a specialized meaning for “origin stories.” They are accounts that relate how superheroes got their superpowers. Some origin stories are based on real people and events, while others are based on more imaginative accounts. Origin stories can contain powerful, emotional symbols that convey profound truths, but not necessarily in a literal sense. In the United States, many people tell stories about Santa Claus. But everyone, except young children, knows that he is a symbol of love and generosity, not a person who actually exists. Many cultures tell stories that seem strange to outsiders but have deep meaning to group members. When people in a culture become literate, they write down their origin stories. But the stories frequently go back way before written records, to when people told them aloud. This is called an “oral tradition.” Multiple versions of each story often exist, since people — from group to group and generation to generation — may change them slightly as they retell them. I have chosen to summarize, in writing, five origin stories from a wide number of places and eras — feel free to tell them aloud to each other. [Sources and attributions]

Chinese Origin Story: Pan Gu and the Egg of the World Compiled by Cynthia Stokes Brown First written down about 1,760 years ago, this story of how the Universe began was told orally long before that. This origin story comes from Chinese culture. It was first written down about 1,760 years ago, roughly 220 — 265 CE, yet it must have been told orally long before that. In the beginning was a huge egg containing chaos, a mixture of yin and yang — female-male, aggressive-passive, cold-hot, dark-light, and wet-dry. Within this yin and yang was Pan Gu, who broke forth from the egg as the giant who separated chaos into the many opposites, including Earth and sky. Pan Gu stood in the middle, his head touching the sky, his feet planted on Earth. The heavens and the Earth began to grow at a rate of 10 feet a day, and Pan Gu grew along with them. After another 18,000 years the sky was higher and Earth was thicker. Pan Gu stood between them like a pillar 30,000 miles in height, so they would never again join. When Pan Gu died, his skull became the top of the sky, his breath became the wind and clouds, his voice the rolling thunder. One eye became the Sun and the other the Moon. His body and limbs turned into five big mountains, and his blood formed the roaring water. His veins became roads and his muscles turned to fertile land. The innumerable stars in the sky came from his hair and beard, and flowers and trees from his skin. His marrow turned to jade and pearls. His sweat flowed like the good rain and the sweet dew that nurtures all things on Earth. Some people say that the fleas and the lice on his body became the ancestors of humanity. Sources David Leeming and Margaret Leeming, A Dictionary of Creation Myths (New York and Oxford: Oxford University Press, 1994), 47 – 50. Image Credits An illustration of Pan Gu from the Sancai Tuhui, public domain Cassia-Tree Moon © Asian Art & Archaeology, Inc./CORBIS

Mayan Origin Story: The Popul Vuh Creation by Diego Rivera © Christie’s Images/CORBIS Compiled by Cynthia Stokes Brown This is the beginning of a long, complex story called the Popol Vuh which means “council book.” It was told by the Mayans who long ago lived in theYucatán Peninsula of Mexico. This origin story was told by the Mayas, who lived in the Yucatán Peninsula of Mexico from around 250 CE to 900 CE. It’s the beginning of a long, complex story called the Popol Vuh (literally the “council book”), first translated into alphabetic text from Mayan hieroglyphics in the 16th century. Now it still ripples, now it still murmurs, still sighs, and is empty under the sky. There is not yet one person, not one animal, bird, fish or tree. There is only the sky alone; the face of earth is not clear, only the sea alone is pooled under all the sky. Whatever might be is simply not there. There were makers in the sea, together called the Plumed Serpent. There were makers in the sky, together called the Heart of Sky. Together these makers planned the dawn of life. The earth arose because of them. It was simply their word that brought it forth. It arose suddenly, like a cloud unfolding. Then the mountains were separated from the water. All at once great mountains came forth. The sky was set apart, and the earth was set apart in the midst of the waters. Then the makers in the sky planned the animals of the mountains — the deer, pumas, jaguars, rattlesnakes, and guardians of the bushes. Then they established the nests of the birds, great and small. “You precious birds; your nests are in the trees and bushes.” Then the deer and birds were told to talk to praise their makers, to pray to them. But the birds and animals did not talk; they just squawked and howled. So they had to accept that their flesh would be eaten by others. The makers tried again to form a giver of respect, a creature who would nurture and provide. They made a body from mud, but it didn’t look good. It talked at first but then crumbled and disintegrated into the water. Then the Heart of Sky called on the wise ones, the diviners, the Grandfather Xpiyacoc and the Grandmother Xmucane, to help decide how to form a person. The Grandparents said it is well to make wooden carvings, human in looks and speech. So wooden humans came into being; they talked and multiplied, but there was nothing in their minds and hearts, no memory of their builder, no memory of Heart of Sky. Then there came a great destruction. The wooden carvings were killed when the Heart of Sky devised a flood for them. It rained all day and all night. The animals came into the homes of the wooden carvings and ate them. The people were overthrown. The monkeys in the forest are a sign of this. They look like the previous people — mere wooden carvings. The story continues with the final people being made from corn, an important crop that enabled the Maya to move from being a hunting-and-gathering society to a more complex civilization. For Further Discussion Are you having any trouble filling out your chart? Ask for help—or offer it—in the Questions Area below. Sources Edited from Dennis Tedlock, Popol Vuh: The Mayan Book of the Dawn of Life Rev. ed. (New York: Simon and Schuster, 1996), 64 – 73. Image Credits Creation by Diego Rivera© Christie’s Images/CORBIS

Modern Scientific Origin Story: The Big Bang Planetary nebula NGC 6210 in Hercules Constellation © ESA/Hubble and NASA By Cynthia Stokes Brown From vast nothingness to a Universe of stars and galaxies and our own Earth. This version of modern science’s origin story is condensed and interpreted from a great body of historical and scientific information. In the beginning, as far as we know, there was nothing. Suddenly, from a single point, all the energy in the Universe burst forth. Since that moment 13.8 billion years ago, the Universe has been expanding — and cooling down as it gets bigger. Gradually energy cooled enough to become matter. One electron could stay in orbit around one proton to become an atom of hydrogen. Great clouds of hydrogen swirled around space until gravity pulled some atoms so close together that they began to burn as stars. Stars swirled together in giant clusters called galaxies; now there are galaxies numbering in the billions. In the beginning, as far as we know, there was nothing. Suddenly, from a single point, all the energy in the Universe burst forth. Since that moment 13.8 billion years ago, the Universe has been expanding — and cooling down as it gets bigger. Gradually energy cooled enough to become matter. One electron could stay in orbit around one proton to become an atom of hydrogen. Great clouds of hydrogen swirled around space until gravity pulled some atoms so close together that they began to burn as stars. Stars swirled together in giant clusters called galaxies; now there are galaxies numbering in the billions. After each star burned up all its matter, it died in a huge explosion. The explosion generated so much heat that some atoms fused and got more and more complex, forming many different elements, including gold and silver. One giant star, our mother star, exploded and scattered clouds of gas containing all the elements needed to form living beings. About 5 billion years ago gravity pulled these atoms into a new star: our Sun. The leftover pieces of matter stuck to each other and formed eight planets, which revolve around the Sun. The third planet out, Earth, became our home. It was the perfect size — not too big, not too small — and the perfect distance from the Sun, not too far or too close. A thin crust formed over Earth’s hot interior, and the temperature was just right for water to form on parts of the surface. Gradually the chemicals in the water formed inside of membranes and got more complex until one-celled living organisms appeared, able to maintain themselves and reproduce. For 3 billion years these one-celled creatures reproduced almost exactly, but not quite. They gradually changed in response to their environment. But they also changed their environment. They learned to burn energy from the Sun, and they released oxygen into the atmosphere. The oxygen formed an ozone layer around Earth that protected life from the Sun’s rays. Eventually cells stuck together to form creatures with many cells. Plants and animals came out of the sea onto land and became ever more complex and aware, until about 100,000 years ago human beings evolved from a shared ancestor with species of apes.Humans could talk in symbols and sing, dance, draw, and cooperate more than the other animals could. Humans learned to write and to accumulate their learning so that it kept expanding. Humans increased in skills and in numbers until there were too many people and too few big animals in some places. Eventually cells stuck together to form creatures with many cells. Plants and animals came out of the sea onto land and became ever more complex and aware, until about 100,000 years ago human beings evolved from a shared ancestor with species of apes. Humans could talk in symbols and sing, dance, draw, and cooperate more than the other animals could. Humans learned to write and to accumulate their learning so that it kept expanding. Humans increased in skills and in numbers until there were too many people and too few big animals in some places. Then humans learned to grow their own food and herd their own animals. Some animals learned to cooperate with humans. This gave humans new sources of food and work energy, and they could live in larger and larger groups. These groups expanded into cities and empires, using more and more of the resources of Earth. Humans collaborated and learned collectively in more complex ways; they traveled, traded, and exchanged inventions, creating vast civilizations of astonishing beauty and complexity. Humans were always looking for more energy for their use. About 200 years ago we learned to use the energy from coal — trees that grew more than 300,000 years ago, then were buried underground. Humans learned to burn oil — animal remains buried long ago under the sea. Using these fossil fuels, humans began to change their climate quickly, as the gases released from burning these fuels ascended into the atmosphere. Now humans are in a predicament – our population is increasing rapidly, fossil fuels are running out, we are pushing many plants and other animals into extinction, and we are changing the climate. What are we humans going to do next?*

Complexity & Thresholds By David Christian What does complexity mean, and why is it so important? What role has complexity played in getting us to the world we live in today? One of the central themes of this course is the idea of increasing complexity. In the 13.8 billion years since our Universe appeared, more and more complex things seem to have appeared—and we’re among the most complex of them all. So it’s natural for complex things to fascinate us. Besides, modern human society is so complex that learning how the Universe creates complexity can also teach us something about today’s world. But we shouldn’t assume there’s anything special about complexity or that complex things are necessarily any better than simple things. Remember that complexity can present challenges. What does complexity mean? That’s a tough question and there’s no universally accepted answer. We may feel intuitively that empty space is much simpler than a star, or that a human being is in some sense more complex than an amoeba. But what does that really mean? Here are some ideas that may help you think about complexity during this course. A continuum from simple to complex Complexity is a quality, like “hot” or “cold.” Things can be more or less simple and more or less complex. At one end is utmost simplicity, like the cold emptiness of intergalactic space. At the other extreme is the complexity of a modern city. The qualities of more complex things Here are three qualities that make some things more complex than others. Diverse ingredients: More complex things often have more bits and pieces, and those bits and pieces are more varied.Precise arrangement: In simpler things it doesn’t matter too much how the ingredients are arranged, but in complex things the bits and pieces are arranged quite precisely. Think of the difference between a car and all the bits and pieces of that car after it’s been scrapped and is lying in a junkyard.Emergent properties: Once the ingredients are arranged correctly, they can do things that they couldn’t do when they weren’t organized. A car can get you around; its component parts cannot. A car’s capacity to be driven is a quality that “emerges” once it’s been assembled correctly, which is why it’s called an “emergent property.” Diverse ingredients: More complex things often have more bits and pieces, and those bits and pieces are more varied. Precise arrangement: In simpler things it doesn’t matter too much how the ingredients are arranged, but in complex things the bits and pieces are arranged quite precisely. Think of the difference between a car and all the bits and pieces of that car after it’s been scrapped and is lying in a junkyard. Emergent properties: Once the ingredients are arranged correctly, they can do things that they couldn’t do when they weren’t organized. A car can get you around; its component parts cannot. A car’s capacity to be driven is a quality that “emerges” once it’s been assembled correctly, which is why it’s called an “emergent property.” Complexity is fragile There’s another important thing to remember about complexity. Complex things need just the right ingredients and they need to be assembled in just the right way. So, complex things are usually more fragile than simple things. And that means that after a time, they fall apart. If they are living creatures, we say they “die.” Death, or breakdown, seems to be the fate of all complex things, though it may take billions of years for a star to break down, and just a day or two for a mayfly to die. The Second Law of Thermodynamics Creating complex things is more difficult than creating simple things. The natural tendency of the Universe seems to be for things to get less and less organized. Think of your own house if you just let it be for a month. Tidying your room means arranging everything in just the right way; it takes work. But if you don’t care how it’s arranged you can just let it un-tidy itself naturally. The idea that the Universe tends naturally to get less ordered and less complex is expressed in one of the most fundamental of all the laws of physics: the Second Law of Thermodynamics. That’s one way of explaining why making complex things requires more work, and thus more energy, than making simple things. Why complexity is rarer than simplicity The Second Law of Thermodynamics explains why most of the Universe is simple. Intergalactic space is almost completely empty, extremely cold, and randomly organized. Complexity is concentrated in just a few places: inside galaxies and particularly around stars. Goldilocks Conditions You find complex things only where the conditions are just right for making them, where there are just the right environments, just the right ingredients, and just the right energy flows. We call these conditions “Goldilocks Conditions.” Remember the children’s story of the three bears? Goldilocks enters their house when they are out. She tastes their porridge and finds that the father bear’s is too hot, the mother bear’s is too cold, but the baby bear’s is just right. Complexity seems to appear only where the conditions are “just right.” So whenever we see complex things appearing, we can ask why the Goldilocks Conditions were “just right.” Here’s an example. You always need energy. So if there’s no energy flowing, it’s hard to build complexity. Think of a still, calm lake that’s been dammed. Not much is happening. Then imagine opening the gates of the dam and allowing the water to flow downhill. Now you have energy flowing—enough to drive a turbine that can create the electricity to power a computer. Now more complex things can happen. But of course there mustn’t be too much energy. If there’s too much water pressure then the turbine will be destroyed. So you need just the right amount of energy—not too little, not too much. Thresholds of increasing complexity In this course, we will focus on moments when more complex things seemed to appear, things with new emergent properties. We call these “threshold moments.” Examples include the appearance of the first stars in a Universe that had no stars, and the appearance of the first cities in societies that had never known cities before. Each time we cross one of these thresholds we’ll ask about the ingredients and the Goldilocks Conditions. And we’ll also ask what was new. What emergent properties do these new complex things have? There are many such turning points in Big History, but in this course we will focus mainly on eight threshold moments. Some thresholds took place at a very specific point in time, while others were more gradual and we can only approximate the turning point. If this were an astronomy course or a biology course, our choice of thresholds would undoubtedly be different. In fact, during this course we will see many important “turning points” that we could, perhaps, describe as “thresholds.” For Further Discussion Think about the your life in terms of thresholds of increasing complexity. What Goldilocks Conditions allowed your thresholds to emerge? What were the emergent properties? Post your answers in the Questions Area below. [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. Reading 1: Skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Reading 2: Understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: What were some challenges Chien-Shiung Wu faced as she became a physicist? How did she overcome these challenges?What does this comic mean by saying the Universe is “left-handed”? What role did Wu play in this discovery?Why was Wu’s 1956 experiment important to collective learning?Looking at just the images in this comic, what information does the artist tell you with the art? What were some challenges Chien-Shiung Wu faced as she became a physicist? How did she overcome these challenges? What does this comic mean by saying the Universe is “left-handed”? What role did Wu play in this discovery? Why was Wu’s 1956 experiment important to collective learning? Looking at just the images in this comic, what information does the artist tell you with the art? Reading 3: Evaluating and Corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: Had you heard about Chien-Shiung Wu before reading this comic? Why do you think someone like Wu isn't featured in more of the big stories about collective learning? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. Dr. Wu and the Left-Handed Universe (Graphic Biography) Writer: Bennett Sherry Artist: Kay Shohini Chien-Shiung Wu is today known as the “First Lady of Physics.” Yet, many people don’t know her name. She broke barriers and disproved one of the fundamental laws of physics. Download the Graphic Biography PDF here or click on the image above.

Evidence for an Expanding Universe By Cynthia Stokes Brown Born: November 20, 1889; Marshfield, Missouri. Died: September 28, 1953; San Marino, California. Edwin Hubble © SPL / Photo Researchers, Inc. In the course of five years, Edwin Hubble twice changed our understanding of the Universe, helping to lay the foundations for the Big Bang theory. First he demonstrated that the Universe was much larger than previously thought, then he proved that the Universe is expanding. Early Life and Education Edwin Powell Hubble, the son of an insurance executive, was born in Marshfield, Missouri, on November 20, 1889, and moved to Wheaton, Illinois, a suburb of Chicago, soon after. Growing up, he was more outstanding as an athlete than as a student, although he did earn good grades in every subject (except spelling). He won seven first-places and a third place in a single high school track-and-field meet in 1906. That year he also set the Illinois high school record in the high jump. At the University of Chicago, Hubble studied mathematics, astronomy, and philosophy — and played for the school’s basketball team. He graduated with a bachelor of science in 1910, and then spent 1911 to 1914 earning his master’s as one of Oxford University’s first Rhodes scholars. Though he studied law and Spanish there, his love of astronomy never diminished. Edwin Hubble © Science Source At Yerkes Observatory Moving back to the United States, Hubble enrolled as a graduate student at the University of Chicago and studied the stars at their Yerkes Observatory in Wisconsin. It was here that he began to study the faint nebulae that would be the key to his greatest discoveries. After receiving his doctorate in astronomy from the University of Chicago in 1917, he won an offer to join the staff at the prestigious Mount Wilson Observatory, near Pasadena, California. At Mount Wilson Observatory Arriving at Mount Wilson in 1919, he joined an astronomy establishment that was just beginning to grasp cosmic distances. The key to that effort was work that had been done studying Cepheid variable stars, roughly a decade earlier, by Henrietta Swan Leavitt at Harvard. These stars brighten and dim in a predictable pattern, and their distance from us can be worked out by measuring how bright they appear to us. Another astronomer at the observatory, Harlow Shapley, built on Leavitt’s findings and shocked the world with his conclusions about the size of the Milky Way. Using the Cepheid variables, Shapley judged that the Milky Way was 300,000 light years across — 10 times bigger than previously thought. Hubble began his work at Mount Wilson just as the new 2.56-meter Hooker Telescope, the most powerful on Earth, was completed. With it, he was able to peer into the sky with greater detail than anyone had previously. After years of observation, Hubble made an extraordinary discovery. In 1923 he spotted a Cepheid variable star in what was known as the Andromeda Nebula. Using Leavitt’s techniques, he was able to show that Andromeda was nearly 1 million light years away and clearly a galaxy in its own right, not a gas cloud. Hubble used the Hooker Telescope at Mount Wilson Observatory for some of his most important discoveries. © Emilio Segrè Visual Archives / American Institute of Physics / Photo Researchers, Inc. Hubble then went on to discover Cepheids in multiple nebulae, and proved, in a 1924 paper called “Cepheids in Spiral Nebula,” that galaxies existed outside our own. Overnight, he became the most famous astronomer in the world, and people everywhere had to get used to the fact that the Universe was far vaster than anyone had imagined. Shapley, for one, was shaken by the news. He wrote Hubble, “I do not know whether I am sorry or glad to see this break in the nebular problem. Perhaps both.” In 1926, while developing a classification system for galaxies, Hubble discovered an odd fact: Almost every galaxy he observed appeared to be moving away from the Earth. He knew this because the light coming from the galaxies exhibited redshift. Light waves from distant galaxies get stretched by the expansion of the Universe on their way to Earth. This shifts visible light toward the red end of the spectrum. Building on the work of Vesto Slipher, who measured the redshifts associated with galaxies more than a decade earlier, Hubble and his assistant, Milton Humason, discovered a rough proportionality between the distances and redshifts of 46 galaxies they studied. By 1929 they had formulated what became known as Hubble’s Law. Hubble’s Law basically states that the greater the distance of a galaxy from ours, the faster it recedes. It was proof that the Universe is expanding. It was also the first observational support for a new theory on the origin of the Universe proposed by Georges Lemaitre: the Big Bang. After all, an expanding Universe must once have been smaller. Timeline of Hubble's life. Click here for a larger version. Download PDF. Later Life Hubble achieved scientific superstardom for his discoveries and is still considered a brilliant observational astronomer. He ran the Mount Wilson Observatory for the rest of his life, popularized astronomy through books and lectures, and worked to have astronomy recognized by the Nobel Prize committee. He also played a pivotal role in the design and construction of the Hale Telescope, on Palomar Mountain, California. At 5.08 meters, the Hale was four times as powerful as the Hooker Telescope and existed as the most advanced telescope on Earth for some time. After its completion in 1948, Edwin Hubble was given the honor of first use. When asked by a reporter what he expected to find, Hubble answered: “We hope to find something we hadn’t expected.” For Further Discussion Think about the following question and write your response and any additional questions you have in the Questions Area below. How did Hubble’s work support the Big Bang theory? [Sources and attributions]

A sun-centered view of the universe By Cynthia Stokes Brown Born: February 19, 1473; Torun, Poland. Died: May 24, 1543; Frombork, Poland. An engraving of Copernicus © Copernicus/PoodlesRock/CORBIS In the middle of the 16th century a Catholic, Polish astronomer, Nicolaus Copernicus, synthesized observational data to formulate a comprehensive, Sun-centered cosmology, launching modern astronomy and setting off a scientific revolution. Renaissance man Have you ever heard the expression “Renaissance man”? First coined in the early 20th century, the phrase describes a well-educated person who excels in a wide variety of subjects or fields. The Renaissance is the name for a period in European history, the 14th through the 17th centuries, when the continent emerged from the “Dark Ages” with a renewed interest in the arts and sciences. European scholars were rediscovering Greek and Roman knowledge, and educated Europeans felt that humans were limitless in their thinking capacities and should embrace all types of knowledge. Nicolaus Copernicus fulfilled the Renaissance ideal. He became a mathematician, an astronomer, a church jurist with a doctorate in law, a physician, a translator, an artist, a Catholic cleric, a governor, a diplomat, and an economist. He spoke German, Polish, and Latin, and understood Greek and Italian. Family and studies You might guess that Copernicus’s parents must have been extremely wealthy to provide him with such an education. While that was the case, the family history was a bit more complicated. Nicolaus was born on February 19, 1473, in Torun, in the approximate center of what is now Poland. His father, named Nicolaus Koppernigk, was a copper merchant from Krakow, and his mother, Barbara Watzenrode, was the daughter of a wealthy Torun merchant. Nicolaus was the youngest of four children; he had a brother and two sisters. His father died when he was 10 and his mother at about the same time. His mother’s brother adopted Nicolaus and his siblings and secured the future of each of them. This maternal uncle, Lucas Watzenrode, was a wealthy, powerful man in Warmia, a small province in northeast Poland under the rule of a prince-bishop. Since 1466 Warmia had been part of the kingdom of Poland, but the king allowed it to govern itself. Watzenrode became the prince-bishop in Warmia when Copernicus was 16. Three years later he sent Copernicus and his brother to the University of Krakow, where Copernicus studied from 1492 to 1496. He was in his first year at the university when Columbus sailed to a continent that was then unknown in Europe. Copernicus changed his last name, Koppernigk, to its Latin version while at the university, since scholars used Latin as their common language. At Krakow Copernicus studied mathematics and Greek and Islamic astronomy. After studying at Krakow, Copernicus’s uncle sent him to Italy, where he studied law at the University of Bologna for four years, and then medicine at the University of Padua for two years. These were two of the earliest and best European universities and Copernicus had to travel two months by foot and horseback to reach Italy. At these universities, Copernicus began to question what he was taught. For example, his professors at Krakow taught about both Aristotle’s and Ptolemy’s views of the Universe. However, Copernicus became aware of the contradictions between Aristotle’s theory of the Earth, the Sun and the planets as a system of concentric spheres and Ptolemy’s use of eccentric orbits and epicycles. Even though his professors believed that the Earth was in the center of the Universe and it did not move, Copernicus began to question those ideas. While at the University of Padua, there is some evidence that he had already developed the idea of a new system of cosmology based on the movement of the Earth. Copernicus returned to Warmia in 1503, at age 30, to live in his uncle’s castle and serve as his secretary and physician. He stayed at this job, which gave him free time to continue his observations of the heavens, until 1510, two years before his uncle’s death. Life as a canon Copernicus’s uncle arranged for him a secure life as a church canon. A canon was a member of a group of canons, called a chapter, who together were responsible for administering all aspects of a cathedral. Canons were encouraged, but not required, to take full orders as a priest. They could take minor orders, but even minor orders included a vow of celibacy. It is not clear whether Copernicus was ever ordained as a priest. It may be that he took only minor orders, enough to be a canon. Due at least in part to the influence of his uncle, Copernicus was elected in 1497 a canon of the cathedral in Frombork (known as Frauenburg at the time), a town in Warmia on the Baltic Sea coast. Copernicus did not assume his position there until 1510, when he took a house outside the cathedral walls and an apartment inside a tower of the fortifications. He had many duties as canon, including mapmaking, collecting taxes and managing the money, serving as a secretary, and practicing medicine. He led a half-religious, half-secular life and still managed to continue his astronomical observations from his tower apartment. He conducted these with devices that looked like wooden yardsticks joined together, set up to measure the angular altitude of stars and planets and the angles between two distant bodies in the sky. He had a simple metal tube to look through, but no telescope had yet been invented. By 1514 Copernicus had written a short report that he circulated among his astronomy-minded friends. This report, called the Little Commentary, expounded his heliocentric theory. He omitted mathematical calculations for the sake of brevity, but he confidently asserted that the Earth both revolved on its axis and orbited around the Sun. This solved many of the problems he found with Ptolemy’s model, especially the lack of uniform circular motion. In 1520 the Teutonic Knights, a German Catholic military order that had Christianized the pagans in this area and controlled a large area along the Baltic Sea, attacked Frombork. They burned the whole town except for the cathedral. Soon, however, the Polish king drove the Knights out of Warmia, and the canons worked to rebuild the town. By 1531 the bishop-prince of Warmia believed that Copernicus had a mistress, Anna Schilling, whom he called his housekeeper. The next bishop-prince worked persistently to force Copernicus to give up his companion. Lutheran Protestantism was springing up nearby, as cities, dukes, and kings renounced their loyalty to the Catholic Church. The Catholic Church responded by trying to enforce more obedience to its rules. However, Copernicus and Schilling managed to keep seeing each other, although not living together, until much later when she moved to the city of Gdansk. The Copernican model from the Harmonica Macrocosmica atlas by Andreas Cellarius. Copernicus’s view of the Solar System from the 1661 Harmonica Macrocosmia by Cellarius © Bettmann/CORBIS A heliocentric theory By 1532 Copernicus had mostly completed a detailed astronomical manuscript he had been working on for 16 years. He had resisted publishing it for fear of the ensuing controversy and out of hope for more data. Finally, in 1541, the 68-year-old Copernicus agreed to publication, supported by a mathematician friend, Georg Rheticus, a professor at the University of Wittenberg, in Germany. Rheticus had traveled to Warmia to work with Copernicus, and then took his manuscript to a printer in Nuremberg, Johannes Petreius, who was known for publishing books on science and mathematics. Copernicus gave his master work the Latin title De Revolutionibus Orbium Coelestium (translated to English as On the Revolutions of the Celestial Spheres). In this work Copernicus began by describing the shape of the Universe. He provided a diagram to help the reader. In the diagram he showed the outer circle that contained all the fixed stars, much further away than previously believed. Inside the fixed stars were Saturn, then Jupiter and Mars, then Earth, Venus, and Mercury, all in circular orbits around the Sun in the center. He calculated the time required for each planet to complete its orbit and was off by only a bit. A summary of Copernicus’s theory 01 - The center of the Earth is not the center of the Universe, only of Earth’s gravity and of the lunar sphere.02 - The Sun is fixed and all other spheres revolve around the Sun. (Copernicus retained the idea of spheres and of perfectly circular orbits. In fact, the orbits are elliptical, which the German astronomer Johannes Kepler demonstrated in 1609.)03 - Earth has more than one motion, turning on its axis and moving in a spherical orbit around the sun.04 - The stars are fixed but appear to move because of the Earth’s motion. 01 - The center of the Earth is not the center of the Universe, only of Earth’s gravity and of the lunar sphere. 02 - The Sun is fixed and all other spheres revolve around the Sun. (Copernicus retained the idea of spheres and of perfectly circular orbits. In fact, the orbits are elliptical, which the German astronomer Johannes Kepler demonstrated in 1609.) 03 - Earth has more than one motion, turning on its axis and moving in a spherical orbit around the sun. 04 - The stars are fixed but appear to move because of the Earth’s motion. Timeline of Coperinicus's life. Click here for a larger version. Download PDF. Death and legacy Legend has it that Copernicus, in a sickbed when his great work was published, awoke from a stroke-induced coma to look at the first copy of his book when it was brought to him. He was able to see and appreciate his accomplishment, and then closed his eyes and died peacefully, on May 24, 1543. Thus he avoided both scorn and praise. Copernicus was thought to be buried in the cathedral at Frombork, but no marker existed. Some of his bones were finally identified there, with a DNA match from a strand of his hair found in a book owned by him, and in 2010 he was given a new burial in the same spot, now marked with a black granite tombstone. The Roman Catholic Church waited seven decades to take any action against On the Revolutions of the Celestial Spheres. Why it waited so long has been the subject of much debate. In 1616 the church issued a decree suspending On the Revolutions of the Celestial Spheres until it could be corrected and prohibiting any work that defended the movement of Earth. A correction appeared in 1620, and in 1633 Galileo Galilei was convicted of grave suspicion of heresy for following Copernicus’s position. Scholars did not generally accept the heliocentric view until Isaac Newton, in 1687, formulated the Law of Universal Gravitation. This law explained how gravity would cause the planets to orbit the much more massive Sun and why the small moons around Jupiter and Earth orbited their home planets. How long did it take for Copernicus’s ideas to reach the general public? Does anyone nowadays still believe the apparent evidence before their eyes that the Sun moves around the Earth to set and rise? Almost everyone learns in childhood that, despite appearances, the Earth moves around the Sun. Copernicus’s model asked people to give up thinking that they lived in the center of the Universe. For him the thought of the Sun illuminating all of the planets as they rotated around it had a sense of great beauty and simplicity. For further discussion Think about the following question and write your response and any additional questions you have in the Questions Area below. This article summarizes Copernicus’s theories in four points. Were his theories correct? [Sources and attributions]

Standing on the Shoulders of Invisible Giants By Eman M. Elshaikh The history of science is a history of our collective learning. Historians piece together different conversations to tell a story that crosses centuries and continents Sir Isaac Newton, the famous English scientist, once said, “If I have seen further, it is by standing on the shoulders of giants.” Of course, Newton wasn’t literally standing on the shoulders of giants. Newton was explaining that his ideas didn’t come from him alone. He relied on the ideas of those who came before him. When Newton used the word giant, he meant people who were giants in the scientific community. These were the people who, before him, made big contributions to our knowledge. Newton, even though he was a genius himself, knew that he couldn’t have come up with his scientific breakthroughs on his own. That’s probably not a surprise to you. But what you might not know is that some of those giants came from the Islamic world. And that might be surprising because Newton was a European scientist. The Renaissance—and the Scientific Revolution, which came later—started in Europe, so many assume that’s where all the scientists were. But many of the ideas that developed in Europe during the Scientific Revolution in the sixteenth and seventeenth centuries were influenced by the work of earlier scholars in the Islamic world and elsewhere. We often hear about the medieval period as a “dark age,” but that’s not quite accurate. From the eighth to the thirteenth century, a golden age of culture and scientific thinking flourished in the Islamic world, which stretched from the Iberian Peninsula (Spain and Portugal) to India. Of course, these scholars also stood on the shoulders of giants from Greece, India, and China. Yet despite the giant innovations of Islamic scholars, they have often been left out of the story, making them invisible. So let’s look a little closer at what these “invisible giants” can show us. Collective learning When Newton spoke of standing on the shoulders of giants, he was talking about collective learning—our species’ unique ability to share, preserve, and build upon knowledge over time. It’s a key part of what makes us human. Our creative abilities depend on learning from the work of others—just like Newton did. You rely on collective learning when you learn by reading a book or listening to your teacher. When you use these ideas in a school project, you make your own contribution to collective learning by sharing your ideas with others. In that way, you become a part of the chain of collective learning. Sometimes it’s easy to see how collective learning moves from one thinker to another, or one community to another. For example, we know that the great astronomer Nicolaus Copernicus directly influenced two other famous astronomers: Galileo Galilei and Johannes Kepler. If we think of Copernicus as a giant, we can say that Galileo and Kepler stood on his shoulders to reach greater heights. And our friend Newton stood on their shoulders to reach even higher. These thinkers lived in different times and places, but we can imagine collective learning as a kind of conversation they had across time and distance. They might never have met, but the transfer of their ideas across time and space allowed science theories to be built, questioned, and refined. These conversations aren’t exactly easy to spot. Historians of science have to work hard to find the evidence that connects one thinker to another. We know about some of these links because historians pieced together the story from a variety of documents. One of the things that makes this so hard is that these documents are located in different countries and written in different languages. Some are better preserved than others. Collecting and translating is already a big challenge, but then historians must put them together and make arguments. These documents are sometimes incomplete or missing, which makes the job even harder. And in many cases, historians just haven’t gotten around to reading them yet. There are thousands of manuscripts that historians are still reading and analyzing so they can uncover stories about the history of science still waiting to be told! The further you go back in time, the harder it is. Copernicus and Newton weren’t separated by that much time or distance, at least compared to the wide separation of Copernicus from Islamic scholars like the Persian astronomer Nasir al-Din al-Tusi, who lived centuries before Copernicus and thousands of miles away! Collective learning is like a conversation that happens across time and space. Over millennia and across continents, humans have contributed to our collective knowledge by writing, publishing, talking, teaching, analyzing, debating, collaborating, and sharing ideas. © DrAfter123 / DigitalVision / Getty Images. We have to wonder: how many invisible giants are still out there? How will we discover them? Which scholars have had their contributions to science erased by time and distance? Probably quite a few. There are a lot of reasons they don’t appear in the historical record. They might be “invisible” because historians just don’t know much about them yet. Even if historians do know about them, they may debate who influenced whom and how much of an influence there really was. Unlike students and scholars today, who carefully write down their sources and references, scientists in the past didn’t always do this. Scientists often borrowed the ideas of others without giving them credit directly. So, historians must connect the dots in other ways. One way is by noticing similarities between two scientists’ work, and then researching how a scientist in one place might have influenced another scientist who lived very far away in a different time. You know that story of Newton discovering gravity by watching an apple fall? That’s called an “aha! moment” and stories of scientific geniuses are full of them. But there is a lot more to collective learning than aha! moments. Adaptations, conversations, arguments, and changes are what keep the scientific conversation going, century after century. Yes, it includes Newton, Copernicus, and al-Tusi, but also included are students and teachers, librarians and writers, historians and astronomers, and you! A bigger history of science To really think about collective learning, we have to tell bigger stories that include once-invisible giants. While Copernicus influenced many scientists, we have to ask: who influenced Copernicus? On whose shoulders did he stand? Copernicus is said to have started the Scientific Revolution, but was there no science before him? Some historians say, “Of course there was—in Europe, China, India, the Islamic world, and beyond!” Historians of science today are beginning to uncover many of these connections. For example, some think Copernicus was influenced by Persian astronomers like al-Tusi. For that matter, al-Tusi was influenced by Chinese and ancient Greek astronomers. Plus, al-Tusi couldn’t have done his mathematical calculations without Arabic numerals—which are really based on a numbering system developed in ancient India. And—oh, wait!—those were introduced earlier by the Persian mathematician al-Khwarizmi. These connections are part of our Big History, because they add to our collective learning. It happens across continents and across centuries. Throughout this course, you’ll learn about important moments in our collective learning. You might wonder why you haven’t heard about these scholars before. Well, it’s still a pretty new field of history! Historians of science continue to learn, debate, and write about it. They argue over who the giants are and how their ideas traveled. Our collective learning about the topic is still growing—and we learn new things every day. It’s a complicated story, but it’s definitely worth telling, especially when it has the power to make invisible giants more visible Author bio Eman M. Elshaikh holds an MA in social sciences from and is pursuing a PhD at the University of Chicago, where she also teaches writing. She is a writer and researcher, and has taught K-12 and undergraduates in the US and in the Middle East. Eman was previously a World History Fellow at Khan Academy, where she worked closely with the College Board to develop curriculum for AP world history. [Sources and attributions]

Measuring Distance in the Universe By Cynthia Stokes Brown Born: July 4, 1868; Lancaster, Massachusetts. Died: December 12, 1921; Cambridge, Massachusetts. Henrietta Leavitt © Photo Researchers Henrietta Leavitt discovered the relationship between the intrinsic brightness of a variable star and the time it took to vary in brightness, making it possible for others to estimate the distance of these faraway stars, conclude that additional galaxies exist, and begin mapping the Universe. Early life and education Henrietta Swan Leavitt was a minister’s daughter whose family moved frequently. When she was about 14, the family moved to Cleveland, Ohio, and in 1885 Leavitt enrolled in Oberlin College to prepare for the strict entrance requirements of the college she really wanted to attend — the Society for Collegiate Instruction of Women, later known as Radcliffe College (now part of Harvard University), in Cambridge, Massachusetts – a dream she achieved at age 20. She discovered her calling in her senior year when she took a course in astronomy. At the Harvard College Observatory Leavitt liked astronomy so much that after graduation she became a volunteer at the Harvard College Observatory as a “computer.” This was the name used for women who examined tiny dots on time-exposed photographs of the night sky and then measured, calculated, and recorded their observations in ledger books. Eventually, in 1902, Leavitt was hired at 30 cents an hour; she continued to work at the observatory for the remaining 19 years of her life. Leavitt took a special interest in the Magellanic Clouds, a pair of luminous hazes now known to be irregular galaxies, the nearest ones to our Milky Way. At the time, no one knew what the clouds were. Since the Magellanic Clouds are only visible in the southern hemisphere, Leavitt could not see them directly. She could merely look at photographic plates taken at Harvard’s auxiliary observatory, in Arequipa, Peru, and sent to Cambridge by ship around the tip of South America. Using Cepheid variables One of Leavitt’s jobs was to examine the variable stars, which, unlike most stars, vary in brightness because of fluctuations within themselves. In the course of her work, Leavitt discovered 2,400 new variable stars, half the known ones in her day. A certain group of variable stars, later called Cepheid variables, fluctuate in brightness (luminosity) in a regular pattern called their “period.” This period ranges from about one day to nearly four months. By comparing thousands of photographic plates, Leavitt discovered a direct correlation between the time it takes for a Cepheid variable to go from bright to dim and back to bright, and how bright the star actually is (its “intrinsic brightness”). The longer the period of fluctuation, the brighter the star. This meant that even though a star might appear extremely dim, if it had a long period it must actually be extremely large; it appeared dim only because it was extremely far away. By calculating how bright it appeared from Earth and comparing this to its intrinsic brightness, one could estimate how much of the star’s light had been lost while reaching Earth, and how far away the star actually was. Leavitt published her first paper on the period-luminosity correlation in 1908. Four years after that, she published a table of the periods of 25 Cepheid variables. Nine years later, in 1921, she died of cancer at age 53 in Cambridge. Timeline of Leavitt's life. Click here for a larger version. Download PDF. Leavitt’s Legacy Before Leavitt established the period-luminosity relationship, astronomers could determine cosmic distances out only about 100 light years. Using her insights, astronomers were able to estimate the Magellanic Clouds to be in the range of 100,000 light years from Earth — much further than anyone had imagined — meaning they could not be within the Milky Way galaxy. The largest telescope then in existence opened in 1904 at Mount Wilson, near Los Angeles, California. In 1919, the astronomer Edwin Hubble took a job there, after finishing his PhD in astronomy at the University of Chicago. Using the Mount Wilson telescope and building on Leavitt’s work, Hubble located Cepheid variables so far away that they conclusively established the presence of other galaxies. By 1925, most astronomers agreed that our galaxy is one among a multitude — a small outpost in a Universe full of galaxies. Leavitt initially worked under a director of the Harvard College Observatory who did not encourage theorizing but preferred only to accumulate data. A later director even tried to take some of the credit for her work after her death. Now, however, Leavitt is recognized as a key contributor to our understanding of the size of the Universe. A modest life Leavitt never married. She gradually became deaf, starting with an illness when she was a young adult. She was buried in Cambridge in the family plot, near the graves of Henry and William James. Her total estate was appraised at $314.91. In her obituary, a senior colleague wrote: “[She] was possessed of a nature so full of sunshine that, to her, all of life became beautified and full of meaning.” [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. Reading 1: Skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Reading 2: Understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: What does the portion of the comic involving bathroom doors tell you about Vera's experience as a scientist?What does the comic mean by saying the Vera's most important observation was something we can't see?What evidence did Vera use to uncover the existence of dark matter?What does Vera mean in the quote at the top of the page: "We're out of kindergarten, but only in about third grade"?How was the artist designed the page, text, and illustrations to tell you about Vera's observations and career? What does the portion of the comic involving bathroom doors tell you about Vera's experience as a scientist? What does the comic mean by saying the Vera's most important observation was something we can't see? What evidence did Vera use to uncover the existence of dark matter? What does Vera mean in the quote at the top of the page: "We're out of kindergarten, but only in about third grade"? How was the artist designed the page, text, and illustrations to tell you about Vera's observations and career? Reading 3: Evaluating and Corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: What does this biography tell you about how our understanding of the Universe has changed? How did perceptions of Vera's observations change over time? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. Revealing the Dark: Vera Rubin (Graphic Biography) Writer: Bennett Sherry Artist: Kay Sohini Vera Rubin’s observations revealed that our Universe is largely composed of matter we cannot see. Her work was met with skepticism, but she transformed astronomy. Download the Graphic Biography PDF here or click on the image above.

All of the following terms appear in this unit. The terms are arranged here in alphabetical order. astronomy — The branch of science that deals with the Universe and the various objects, like stars, planets, and galaxies, that we find within it. Cosmology and astrophysics are closely related to astronomy, and the words are sometimes used interchangeably. Cosmology focuses on the Universe’s largest scales in space and time, and astrophysics focuses on the properties and interactions of astronomical objects. atom — A small unit of matter composed of protons, electrons, and usually neutrons. Atoms are basic building blocks of the matter we see in the Universe and on Earth. The number of protons in the nucleus of an atom determines which chemical element it is. authority — A respectable or credible source; an expert. Big Bang — A theory, first articulated in the 1920s, proposing that the Universe started out extremely hot and dense and gradually cooled off as it expanded. Cepheid — A star that fluctuates in brightness and provides astronomers with a reference they can use to measure great distances in the Universe. It was the identification of Cepheids in nearby galaxies that first proved that the Universe consists of more than one galaxy. claim — An assertion that something is true. claim testing — The use of strategies to decide whether a story or concept should or should not be trusted. The four strategies for claim testing that we use in Big History are intuition, authority, logic, and evidence. collective learning — The ability to share, preserve, and build upon ideas over time. Cosmic Microwave Background (CMB) or Cosmic Background Radiation (CBR) — Low-energy radiation pervading the entire Universe, released about 380,000 years after the Big Bang. At this point, the Universe had cooled sufficiently for atoms to form and allow radiation and matter to separate. cosmology — The study of the Universe on its largest scales, including its origin and structure. Doppler effect — The apparent stretching out or contraction of waves because of the relative movement of two bodies. The Doppler effect explains why an ambulance siren seems higher when the ambulance is traveling toward you than when it is moving away. It also helps astronomers identify whether objects such as stars or galaxies are moving toward us or away from us. electromagnetism — One of the four fundamental forces or interactions, along with gravity, the weak nuclear force, and the strong nuclear force. Among other things, electromagnetism is responsible for the interaction between electrically charged particles, including holding electrons and protons together to form atoms. Electromagnetism is also responsible for essentially all molecular interactions. electron — A negatively charged subatomic particle that orbits the nucleus of an atom. energy — The capacity to do work, associated with matter and radiation. Includes kinetic energy, potential energy, and chemical energy, among others. evidence — Concrete, verifiable information that either supports or disproves a claim. gravity — The fundamental force of attraction between any two objects that have mass. helium — The second simplest of all chemical elements, helium has two protons and (almost always) two neutrons. Helium was produced soon after the Big Bang. hydrogen — The simplest of all chemical elements, hydrogen has one proton. Hydrogen was the first element produced after the Big Bang and is the most common element in the Universe. inflation — The idea that space and time (space-time) underwent an expansion at a rate much faster than the speed of light during the first 10-36 seconds after the Big Bang. intuition — A “gut feeling” that is not necessarily based on logic or evidence. light-year — A measure of distance in space; the distance that light travels in a vacuum in one year. It is equal to roughly 9.5 trillion kilometers, or 5.9 trillion miles. logic — The application of systematic reasoning to arrive at a conclusion. matter — The physical material of the Universe, including subatomic particles, atoms, and the substances that are built out of them. neutron — An electrically neutral subatomic particle present in the nuclei of most atoms. Unlike protons, the number of neutrons in a given element can vary, giving rise to different isotopes of an element. nucleus (atomic) — The extremely dense and positively-charged region at the center of an atom that consists of protons and neutrons. parallax — The change in the apparent position of an object caused by movement of the observer. proton — A subatomic particle with a positive electric charge. The number of protons in an atom (the atomic number) determines which element it is: For example, carbon atoms always have 6 protons, while iron atoms always have 26 protons. redshift — The phenomenon in which light waves from distant galaxies are “stretched out,” which for visible light means a shift toward the red side of the spectrum. Redshift provides scientists with strong evidence that the Universe is expanding, since the expansion of space explains the stretching of the light waves. scientific method — The process of gathering evidence to test and refine scientific theories. space-time — The unification of space and time into a single four-dimensional continuum or “fabric.” Space makes up three of the dimensions, while time makes up the fourth, and cannot be fully separated from space. Albert Einstein’s General Theory of Relativity holds that all objects with mass interact with space-time by bending it much like a person standing on a trampoline bends the trampoline. telescope — An instrument used for viewing distant objects, including planets, stars, and galaxies. thermodynamics (first law of) — One form of the law of conservation of energy, which states that energy may change forms but cannot be created or destroyed.

Browse through different views of the Universe and zoom in on the light from distant stars to better understand how our understanding of cosmology has evolved. Ptolemy's Universe Source: Big History ProjectThe Ptolemaic view of the Universe was an Earth-centered, or geocentric, model. The Sun and all of the planets orbited the Earth and the other stars formed a backdrop that also orbited Earth. Source: Big History Project The Copernican Model The idea of a Sun-centered, or heliocentric, view of the Universe had been suggested by ancient Greek astronomers like Aristarchos and was later published by Polish astronomer Nicolaus Copernicus in 1543. To some extent, this model (not at actual scale in this illustration) ushered in a new age of astronomy. Kepler and Elliptical Orbits The German astronomer and mathematician Johannes Kepler demonstrated that the orbits of Earth and the other planets (not drawn to scale in this illustration) were not perfectly circular but were actually elliptical, or egg-shaped. Redshift This illustration simulates the redshift, or Doppler shift, that affects how light waves appear to us when the source of light is moving away. When we view galaxies from Earth, their light is shifted to the red side of the color spectrum, an indication that they are moving away from us. This is strong evidence for an expanding Universe. The Electromagnetic Spectrum It's important to remember that what we see as visible light is only a small portion of the full electromagnetic spectrum. Many modern telescopes are able to view different wavelengths of electromagnetic energy, thus generating images from space that are completely invisible to the unaided eye. Spectral Lines The color of light from objects in space can be used for more than gauging distances. Different elements actually leave their own "signatures" in light. Scientists can use spectral lines to determine the chemical composition of objects in space like other stars and planets. Hydrogen, helium, and oxygen are the three most abundant elements in the Universe. Cepheid Variable Star V1 in the Andromeda Galaxy Source: NASA, ESA, the Hubble Heritage Team Astronomers use the fluctuating brightness of Cepheid variable stars like V1 as "stellar yardsticks" to measure distances. The discovery of Cepheids and the understanding of how to interpret their fluctuations of brightness helped prove that the Universe was a much larger place than first thought. Cepheids in the Galaxy NGC 5584 Source: NASA, ESA, L. Frattare (STScl), A. Riess (STScl/JHU) and L. Macri (Texas A & M University) This illustration shows the location of the many Cepheid variable stars found in the spiral galaxy NGC 5584. Different Cepheids have different "periods" related to the total energy they put out as they burn hydrogen and helium. The Horn Antenna Source: NASA The Horn reflector antenna at Bell Telephone Laboratories in Holmdel, New Jersey was built in 1959 and became famous when Arno Penzias and Robert Wilson used it to detect the Cosmic Microwave Background (CMB), the afterglow of the Big Bang. In 1989 The Horn was dedicated to the U.S. National Park Service as a National Historic Landmark. The Cosmic Microwave Background Source: NASA/WMAP Science Team These details of the CMB were captured by NASA's Wilkinson Microwave Anistropy Probe (WMAP) at the very start of the 21st century. The color-enhanced WMAP imagery of the infant Universe shows the slight variations in temperature that correspond to the slight variations in density that helped seed the formation of the first galaxies.

The Missing Link? The Maragha Observatory By Eman M. Elshaikh From Ptolemy to Copernicus and Galileo, thinkers have debated what the Universe looked like for centuries. Ultimately, scholars moved from an Earth-centered model to a Sun-centered model. How did we get there? Planetary revolutions Television with breaking news is a composite image of the Earth orbiting the Sun, Breaking News lower thirds banner, and television, all via Freepik. Or at least it was big news to people living in the sixteenth century, when this revolutionary idea challenged people’s understanding of the Universe. Ancient astronomers like Ptolemy (100–170 CE) believed that the Earth was at the center of the Universe. They thought the Sun, stars, and planets revolved around Earth. This belief persisted—although some questioned it—for many hundreds of years. By the sixteenth century, however, astronomers like Copernicus (1473–1543 CE) and Galileo (1564–1642 CE), started challenging Ptolemy’s model. They put the Sun at the center. This heliocentric (Sun at the center) model of the Universe shocked people at the time. The Catholic Church even jailed Galileo for claiming it. Like all scholars, Copernicus and Galileo came up with their ideas using the knowledge of those who came before them. What was this earlier knowledge? About 1,400 years separated Copernicus from Ptolemy. But we don’t hear much about the people who came between—who carried on the collective learning conversation between these major figures. For centuries, scholars had been slowly chipping away at the Earth-at-the-center model. The tenth-century Arab astronomer, Ibn al-Haytham (965–1040 CE), for example, questioned Ptolemy’s model. He pointed out several contradictions and claimed that Ptolemy’s idea about how different planets fit together simply didn’t work. An even earlier Arab astronomer, al-Battani (858–929 CE), calculated the movement of the Sun and the planets. His carefully recorded observations were cited by Copernicus many times. So while Copernicus is famous for challenging Ptolemy, there have been missing links in history’s centuries-long chain of thinkers who contributed to this debate. Thanks to the work of many invisible giants like Ibn al-Haytham and al-Battani, it was possible for scholars who came later to construct a serious challenge to such a long-accepted view of the Universe. Many of these invisible giants were astronomers working during the Golden Age of Islam. A golden age during a dark age The scholars between Ptolemy and Copernicus were part of a vibrant tradition of astronomy in the Islamic world. These scholars were supported largely by the wealthy rulers of Islamic empires, and together their work launched a period of scientific and cultural achievement called the Islamic Golden Age. By building on the knowledge of Greek, Indian, Chinese, Babylonian, Persian, and Arab thinkers before them, scholars were able to make new observations and discoveries. Astronomy was a major field for these scholars. For Muslims of this period, astronomy was a practical science that was important for religious practice. By measuring the movement of the Sun, Moon, and stars, Muslim scientists determined the times for daily prayers, set the dates for the lunar calendar, and precisely calculated the direction of Mecca from any location. This knowledge was valuable to Muslim political and religious leaders. As a result, many Muslim rulers built observatories—special buildings for studying astronomy. Among the most famous and important of these was the Maragha Observatory. There, scholars seriously challenged Ptolemy’s Earth-at-the-center system, which had been accepted for many centuries. The geocentric or Earth-centered model of the Universe, which places the Earth at the center of planetary orbits. Ptolemy was one thinker who proposed this model, which was accepted for centuries after Ptolemy’s death. By BHP and Peter Quatch, CC BY-NC 4. The heliocentric or Sun-centered model of the Universe, which places the Sun at the center of planetary orbits. Copernicus was arguably the first scholar to propose this model. By BHP and Peter Quatch, CC BY-NC 4.0. The Maragha Observatory In the thirteenth century, the Mongol ruler Hulagu Khan conquered a big part of the Islamic world. After founding the Ilkhanate of Persia, he destroyed the city of Baghdad, along with the many books in its famed House of Wisdom. Despite the Mongols’ destruction of scientific knowledge in this unfortunate case, they also supported its creation. Like the Arab and Persian rulers who came before them, Mongol rulers supported scholars, especially astronomers. In addition to the practical importance of astronomy to Islam, Mongol rulers believed that studying the stars would help them make decisions and predict the future, so they brought astronomers from across their massive empire to their courts. Once he had finished his wars of conquest, Hulagu Khan worked with the great Persian astronomer Nasir al-Din al-Tusi, and built the Maragha Observatory in Persia. It was the most advanced observatory in the world at the time. It attracted astronomers from across the Islamic world and from as far away as China. Under Mongol rule, astronomers from across Eurasia shared ideas, which sped up new developments in collective learning. Maragha astronomers recorded their astronomical observations and calculations in the massive library at the observatory. Using these observations, they came up with new ideas about how the planets moved. One of the most important of these new ideas was called the “Tusi couple,” named after Nasir al-Din al-Tusi many centuries later. The Tusi couple may sound like the screen name of a pair of adorable lovebirds on Instagram, but it’s actually a mathematical idea. Astronomers used the Tusi couple to create models of a small circle rotating within a larger one, and then track the motion of the rotation. It helped astronomers understand how different celestial bodies revolve around one another. Ibn al-Shatir, a Syrian astronomer, built on this work. Using the Tusi couple, Ibn al-Shatir corrected Ptolemy’s calculations about distances between planetary bodies. Ibn al-Shatir wanted to create a model of the Solar System that fit with the observations he and others had made. His model was much more accurate than Ptolemy’s. While the models coming out of the Maragha Observatory kept the Earth at the center, they made crucial changes to Ptolemy’s model and moved our collective understanding closer to a Sun-centered model. The missing link? Neither Nasir al-Din al-Tusi nor Ibn al-Shatir understood the Sun was at the center of the Solar System. Still, their work may have provided the foundation for Copernicus’s heliocentric model. OK, words like “may have” are frustrating when you want to know if something is true, but not all historians agree on this. The “conversations” among Copernicus, Ptolemy, and the Maragha scholars were spread out over 14 centuries. It’s hard to prove how these ideas developed, moved, or changed, but it’s still important to look for connections. On the one hand, some historians of science argue that scholars like al-Tusi and Ibn al-Shatir influenced Copernicus’s heliocentric system. They use this evidence to support their claims: The work of these scholars had been translated and spread around Eurasia for centuries before Copernicus’s time. It’s logical to assume that an educated man like Copernicus would have come across their work.There are similarities between Copernicus’s diagrams and mathematical arguments and those of the Maragha scholars. Some of Copernicus’s models of planetary rotations used mathematical ideas that were nearly identical to the Tusi couple. Some historians even argue that the diagrams are labeled similarly to Ibn al-Shatir’s.Without this link, it’s more difficult to explain how Copernicus made the leaps that led to his conclusion that the Sun is at the center of our Solar System. The work of these scholars had been translated and spread around Eurasia for centuries before Copernicus’s time. It’s logical to assume that an educated man like Copernicus would have come across their work. There are similarities between Copernicus’s diagrams and mathematical arguments and those of the Maragha scholars. Some of Copernicus’s models of planetary rotations used mathematical ideas that were nearly identical to the Tusi couple. Some historians even argue that the diagrams are labeled similarly to Ibn al-Shatir’s. Without this link, it’s more difficult to explain how Copernicus made the leaps that led to his conclusion that the Sun is at the center of our Solar System. On the other hand, other historians disagree. They don’t think the Maragha Observatory scholars influenced Copernicus’s heliocentric system. They use this evidence to support their claims: While Copernicus cited scholars like al-Battani, he never mentioned al-Tusi or Ibn al-Shatir. (Of course, scientists of this era often borrowed freely from one another and reworked each other’s ideas without giving direct credit.)These Islamic scholars didn’t have a heliocentric model. In fact, their models are pretty different from Copernicus’s.There may be similarities in mathematical ideas, but these mathematical ideas are used very differently.Even if there are some similarities, these historians argue that it’s possible to have similarity without direct influence. They could be independent discoveries. While Copernicus cited scholars like al-Battani, he never mentioned al-Tusi or Ibn al-Shatir. (Of course, scientists of this era often borrowed freely from one another and reworked each other’s ideas without giving direct credit.) These Islamic scholars didn’t have a heliocentric model. In fact, their models are pretty different from Copernicus’s. There may be similarities in mathematical ideas, but these mathematical ideas are used very differently. Even if there are some similarities, these historians argue that it’s possible to have similarity without direct influence. They could be independent discoveries. Historians will continue to debate these questions. You might say that historians are still learning about collective learning. Who learns it? Who collects it? How, over thousands of years, is knowledge shared, moved, changed, translated, improved, and challenged? No matter how historians answer these questions, it’s important to keep revealing the influence of invisible giants like Ibn al-Haytham, al-Battani, al-Tusi, Ibn al-Shatir, and many others. Only then can we start to make connections that allow us to tell our Big History more fully. Author bio Eman M. Elshaikh holds an MA in social sciences from and is pursuing a PhD at the University of Chicago, where she also teaches writing. She is a writer and researcher, and has taught K-12 and undergraduates in the US and in the Middle East. Eman was previously a World History Fellow at Khan Academy, where she worked closely with the College Board to develop curriculum for AP world history. [Sources and attributions]

An Earth-Centered View of the Universe Born: 85 CE; Hermiou, Egypt. Died: 165 CE; Alexandria, Egypt. Portrait of Ptolemy by Andre Thevet © Bettmann/CORBIS By Cynthia Stokes Brown The Earth was the center of the Universe according to Claudius Ptolemy, whose view of the cosmos persisted for 1400 years until it was overturned — with controversy — by findings from Copernicus, Galileo, and Newton. An Astronomer in Ancient Times Claudius Ptolemy (about 85–165 CE) lived in Alexandria, Egypt, a city established by Alexander the Great some 400 years before Ptolemy’s birth. Under its Greek rulers, Alexandria cultivated a famous library that attracted many scholars from Greece, and its school for astronomers received generous patronage. After the Romans conquered Egypt in 30 BCE (when Octavian defeated Cleopatra), Alexandria became the second-largest city in the Roman Empire and a major source of Rome’s grain, but less funding was provided for scientific study of the stars. Ptolemy was the only great astronomer of Roman Alexandria. Ptolemy was also a mathematician, geographer, and astrologer. Befitting his diverse intellectual pursuits, he had a motley cultural makeup: he lived in Egypt, wrote in Greek, and bore a Roman first name, Claudius, indicating he was a Roman citizen — probably a gift from the Roman emperor to one of Ptolemy’s ancestors. A Geocentric View Ptolemy synthesized Greek knowledge of the known Universe. His work enabled astronomers to make accurate predictions of planetary positions and solar and lunar eclipses, promoting acceptance of his view of the cosmos in the Byzantine and Islamic worlds and throughout Europe for more than 1400 years. Ptolemy accepted Aristotle’s idea that the Sun and the planets revolve around a spherical Earth, a geocentric view. Ptolemy developed this idea through observation and in mathematical detail. In doing so, he rejected the hypothesis of Aristarchus of Samos, who came to Alexandria about 350 years before Ptolemy was born. Aristarchus had made the claim that the Earth revolves around the Sun, but he couldn’t produce any evidence to back it up. Map of the Universe according to Ptolemy, from a 17th century Dutch atlas by Gerard Valck © Bettmann/CORBIS Based on observations he made with his naked eye, Ptolemy saw the Universe as a set of nested, transparent spheres, with Earth in the center. He posited that the Moon, Mercury, Venus, and the Sun all revolved around Earth. Beyond the Sun, he thought, sat Mars, Jupiter and Saturn, the only other planets known at the time (as they were visible to the naked eye). Beyond Saturn lay a final sphere — with all the stars fixed to it — that revolved around the other spheres. This idea of the Universe did not fit exactly with all of Ptolemy’s observations. He was aware that the size, motion, and brightness of the planets varied. So he incorporated Hipparchus’s notion of epicycles, put forth a few centuries earlier, to work out his calculations. Epicycles were small circular orbits around imaginary centers on which the planets were said to move while making a revolution around the Earth. By using Ptolemy’s tables, astronomers could accurately predict eclipses and the positions of planets. Because real visible events in the sky seemed to confirm the truth of Ptolemy’s views, his ideas were accepted for centuries until the Polish astronomer, Copernicus, proposed in 1543 that the Sun, rather than the Earth, belonged in the center. After the Roman Empire dissolved, Muslim Arabs conquered Egypt in 641 CE. Muslim scholars mostly accepted Ptolemy’s astronomy. They referred to him as Batlamyus and called his book on astronomy al-Magisti, or “The Greatest.” Islamic astronomers corrected some of Ptolemy’s errors and made other advances, but they did not make the leap to a heliocentric (Sun-centered) universe. Ptolemy’s book was translated into Latin in the 12th century and known as The Almagest, from the Arabic name. This enabled his teachings to be spread throughout Western Europe. We know few details of Ptolemy’s life. But he left one personal poem, inserted right after the table of contents in The Almagest: Well do I know that I am mortal, a creature of one day.But if my mind follows the wandering path of starsThen my feet no longer rest on earth, but standing byZeus himself, I take my fill of ambrosia, the food of the gods. For Further Discussion Think about the following question and write your response and any additional questions you have in the Questions Area below. Even though Ptolemy’s system was wrong, people believed in it. Why? [Sources and attributions]

Father of Modern Observational Astronomy By Cynthia Stokes Brown Born: February 15, 1564; Pisa, Italy. Died: January 9, 1642; Florence, Italy. An undated portrait of Galileo © Bettmann/CORBIS An Italian Renaissance man, Galileo used a telescope of his own invention to collect evidence that supported a Sun-centered model of the Solar System. Youth and Education Galileo Galilei was born in Pisa, Italy, on February 15, 1564, the first of seven children of Vincenzo Galilei and Giulia Ammanati. Galileo’s father was a musician — a lute player — from a noble background that conferred on him the right to hold civic office in the Duchy of Florence, which in 1569 became the Grand Duchy of Tuscany. At the time, Italy was made up of small territories ruled by hereditary dukes. When Galileo was 10, his family moved to Florence, northeast of Rome, where he was educated in a monastery. He was attracted to the priesthood, but his father steered him to study medicine from 1581 to 1585 at the University of Pisa, some 40 miles west of Florence on the coast, and very near Galileo’s childhood home. University studies at that time were based primarily on Aristotle’s philosophy, but Galileo’s acute observations caused him to question some of these accepted views. He noticed that hailstones of different sizes reached the ground simultaneously, contradicting Aristotle’s rule that bodies fall with speeds proportional to their size. At this time Galileo also sat in on lectures by a practical mathematician in the service of the Grand Duke, apart from his university studies. Professor at Pisa and Padua After four years at university Galileo gave private lessons in mathematics and wrote his first scientific paper, about how things float on water. In 1587 he got a position teaching mathematics at the University of Pisa, which paid him a very modest salary. Two years later Galileo’s father died, leaving Galileo responsible for the promised dowries of his two sisters. The next year he secured the chair of mathematics at the renowned University of Padua, and the new position paid three times as much. In addition to mathematics, Galileo gave private instruction in military architecture, fortification, surveying, and mechanics. At the age of 31 Galileo showed his first interest in astronomy, while working to explain the cause of the tides. (Padua was 20 miles inland from Venice, an important trading port on the Adriatic Sea.) Astronomy was considered part of mathematics at the time, while cosmology was part of philosophy. Most scholars still held the views of Ptolemy, who followed Aristotle in thinking that all heavenly bodies revolve around Earth (a geocentric model). But other views were being considered, including that of Copernicus, who claimed that all bodies revolve around the Sun (a heliocentric model), and of Danish astronomer Tycho Brahe, who held that Earth was fixed but other planets are in orbit around the Sun. In 1597 a German visitor gave Galileo a book by German astronomer Johannes Kepler, who was enthusiastically pro-Copernicus. Galileo wrote a letter to Kepler stating that he had long agreed with Copernicus but that he had not dared to make his thoughts public because he was frightened that he would become, like Copernicus, “mocked and hooted by an infinite multitude.” In the same year Galileo invented a mechanical device for mathematical calculations. He had a craftsman make them, so that Galileo could sell them and give classes on how to use them. Professors at Padua tended not to marry, and prominent families there did not view Galileo as a catch. Instead, Galileo established a lasting relationship with a non-noble woman 14 years younger, Marina Gamba, and had three children with her. He never married her, and she and the children lived separately, around the corner from him. When he later left Padua in 1610 to move to Florence, he put their two daughters in a convent as soon as possible, and he left his son, Vincenzo, in Padua in Marina’s care. Galileo’s first known astronomical observation occurred in 1604, when a supernova (the explosive death of a high mass star) was visible in the sky. Such an event clearly challenged Aristotle’s claim that no change could ever take place in the heavens. From then on, observation and experimentation became the basis for Galileo’s work. Galileo’s prominence as a mathematician and scholar grew, and in the summer of 1605 he arranged to tutor Cosimo de Medici, the son of the Grand Duke of Tuscany. In July 1609 Galileo heard about a Dutch device for making distant objects look nearer. A friend who saw it described it to Galileo as having two lenses, one on each end of a four-foot tube. Within about a month Galileo had made an instrument three times as powerful as the Dutch device. Galileo continued to work on his telescope, grinding his own lenses. By December 1609 he had seen for the first time the four largest moons orbiting around Jupiter, which contradicted Ptolemaic theory that Earth is the center of all orbiting bodies. Galileo published his findings in March 1610 as The Starry Messenger; the general public was excited, but most philosophers and astronomers declared it an optical illusion. An engraving of Galileo with his telescope © Mary Evans / PhotoResearchers, Inc Mathematics at the Court of Tuscany Galileo was offered life tenure at the University of Padua, but Florence was his home, and he wanted freedom from teaching. So he took the job of court mathematician in Florence, where his former math student had become Cosimo II, the Grand Duke of Tuscany. Soon after his arrival in Florence in September 1610, Galileo began his observations of Venus. Over time he discovered that the Moon-like phases of Venus demonstrated that the neighboring planet had an orbit independent of Earth. This showed conclusively that Venus circled the Sun, as Copernicus thought, not Earth, as Ptolemy thought. But it did not yet prove conclusively that Earth circled the Sun. In 1613 Galileo published his Letters on Sunspots, based on his observations of the dark spots on the Sun that are caused by intense magnetic activity. In an appendix he noted that he agreed with Copernicus, mentioning the fact that he had seen eclipses of the satellites of Jupiter, further evidence that they orbited the planet. This is the only time that Galileo expressed in print his support of the Copernican model. Galileo had no definitive evidence that Copernicus was right, and he didn’t claim that he did. Galileo’s main pieces of evidence were the phases of Venus, the eclipses of Jupiter’s moons, the existence of tides (which Galileo believed could only occur if the Earth moved), observable planetary speeds, and the distances of planets from the Sun. Drama with the Inquisition During the first part of the 16th century the Catholic Church was facing the challenge of Protestants, who were breaking away from the Catholic Church over certain doctrines. By this time there were printers in many European cities and ideas were spreading quickly, some of them in opposition to the Catholic Church and its beliefs. To combat all heresies, the Pope set up a system of tribunals, or courts, called the Inquisition. In 1616, the year of Shakespeare’s death, the authorities of the Inquisition in Rome decided to prohibit Copernicus’s book, On the Revolutions of the Celestial Spheres, and any other books that argued in favor of a Copernican Sun-centered model for the Solar System. Galileo traveled to Rome to try to prevent this; he thought it was a mistake that would eventually tarnish the church’s reputation. He believed that the Catholic Church should keep science and religion completely separate and not interfere with scientific research. The Church upheld their position and Galileo agreed to obey the ban. In 1623 a Florentine who admired Galileo became Pope Urban VIII. Galileo had six audiences (meetings) with the Pope in 1624 and received permission to publish his theory on the causes of tides, provided he did not take sides on the cosmological debate. For the next six years Galileo worked on this book, which turned into a dialogue concerning the relative merits of the Ptolemaic and the Copernican conceptions of the Universe, without reaching a conclusion of one over the other. To carry out the discussion, Galileo invented three characters: Salviati, who gave Copernicus’s views; Simplicio, who presented Aristotelian/Ptolemaic views; and Sagredo, an interested layman. Simplicio was named for an ancient Greek commentator on Aristotle. The title in English was Dialogue Concerning the Two Chief World Systems–Ptolemaic and Copernican. The publisher of the book received a license to print, and the book appeared in Florence in March 1632. An outbreak of the plague delayed copies being sent to Rome. In August of the same year an order came from the Roman Inquisition to stop all sales. Galileo’s student and friend, the Grand Duke Cosimo II, had died in 1621. The new Grand Duke of Tuscany, Ferdinand, protested the book, which seemed to him, and to many of the church leaders, to portray Simplicio as a simpleton and fool, and thus to take sides in the debate. The Pope considered the character of Simplicio an insult, as did the other church leaders. In September 1632 Galileo was charged with “vehement suspicion of heresy” and ordered to come to Rome for a trial. Ill, he did not appear until February 1633. Galileo denied that he was defending heliocentrism, but he finally admitted that one could get that impression from the book. He was threatened with torture, forced to recant the heliocentric model, and, in June of that year, sentenced to indefinite imprisonment in Rome. His book was put on the Index of Prohibited Books. Three of the ten judges disagreed with the verdict. Legend has it that as Galileo left the courtroom he whispered, “Eppur si muove [Still it (Earth) moves],” but this was most likely invented later. Galileo was crushed by the harsh verdict. The archbishop of Siena, who had disagreed with the verdict, got permission to take Galileo into his home and helped him through his depression. Two years before his trial Galileo had taken a villa on the outskirts of Florence, to be next to the convent where his daughters were nuns. After a few months in Rome, Galileo received permission to return to his own villa, to be guarded by representatives of the Inquisition, a house arrest. He was ill with a hernia, heart palpitations, and insomnia. A few months after his return home his older daughter, Maria Celeste, with whom he was very close, died in April 1634. The following year Galileo’s book, Dialogue Concerning the Two Chief World Systems–Ptolemaic and Copernican, was published in Latin in Strasburg, Alsace (France), outside the grasp of the Catholic Inquisition, thereby reaching a much more cosmopolitan audience than the suppressed Italian text. Timeline of Galileo’s life. Click here for a larger version. Download the PDF. Blindness and a Legacy of Truth Galileo rallied and in his last years wrote a book summarizing all his ideas, published in 1637 in Holland in Italian. This book was translated into English in 1661 as Discourses and Mathematical Demonstrations Relating to Two New Sciences, and Isaac Newton read it in 1666. By 1638 Galileo had become totally blind. He was allowed to live with his son in Florence and have visitors as long as they were not mathematicians. He carried on a great deal of correspondences by dictating his letters to others. He died on January 9, 1642, in Florence, at the age of 77. He was not allowed to be buried in the main body of the Basilica of Santa Croce, but in a small room at the end of a corridor; he was reburied in the main part in 1737. The Catholic Church took 200 years to remove Galileo’s book from the Index of Prohibited Books, finally doing so in 1835. In 1992 Pope John Paul II expressed regret at how the church had handled the issue of Galileo and issued a declaration acknowledging the errors committed by the court of the Catholic Church. In 2008 plans were announced for a statue of Galileo inside the Vatican walls, but in 2009 these plans were suspended. Galileo’s own words to a friend about his blindness serve as a suitable epitaph: Alas, your friend and servant Galileo has for the last month been irremediably blind, so that this heaven, this earth, this universe which I, by my remarkable discoveries and clear demonstrations had enlarged a hundred times beyond what had been believed by wise men of past ages, for me is from this time forth shrunk into so small a space as to be filled by my own sensations. (Drake, p. 107) For Further Discussion Think about the following question and write your response and any additional questions you have in the Questions Area below. How did the telescope contribute to Galileo’s discoveries? [Sources and attributions]

Physics, Gravity & the Laws of Motion By Cynthia Stokes Brown Born: January 4, 1643; Lincolnshire, England. Died: March 31, 1727; London, England. Portrait of Isaac Newton © CORBIS Sir Isaac Newton developed the three basic laws of motion and the theory of universal gravity, which together laid the foundation for our current understanding of physics and the Universe. Early Life and Education Newton was born prematurely and not expected to survive. His dad had died before his birth, and when he was 3 his mother remarried and left him with his grandparents on a farm in Lincolnshire, England, about 100 miles north of London, while she moved to a village a mile and a half away from him. He grew up with few playmates and amused himself by contemplating the world around him. His mother returned when Newton was 11 years old and sent him to King’s School, eight miles away. Rather than playing after school with the other boys, Newton spent his free time making wooden models, kites of various designs, sundials, even a water clock. When his mother, who was hardly literate, took him out of school at 15 to turn him into a farmer, the headmaster, Henry Stokes, who recognized where Newton’s talents lay, prevailed on her to let Newton return to school and prepare for university. Newton attended Cambridge University from 1661 to 1665. The university temporarily closed soon after he got his degree because people in urban areas were dying from the plague. Newton retreated to his grandparents’ farm for two years, during which time he proved that “white” light was composed of all colors and started to figure out calculus and universal gravitation — all before he was 24 years old. It was on his grandparents’ farm that Newton sat under the famous apple tree and watched one of its fruits fall to the ground. He wondered if the force that pulled the apple to the ground could extend out to the Moon and keep it in its orbit around Earth. Perhaps that force could extend into the Universe indefinitely. Isaac Newton performing an experiment © Bettmann/CORBIS At Cambridge After the plague subsided, Newton returned to Cambridge to earn his master’s degree and become a professor of mathematics there. His lectures bored many of his students, but he continued his own thinking and experiments, undaunted. When his mother died, he inherited enough wealth to leave his teaching job and move to London, where he became the president of the Royal Society of London for Improving Natural Knowledge, the top organization of scientists in England, for 25 years. Laws of Motion and Gravity Newton’s most important book was written in Latin; its title was translated as Mathematical Principles of Natural Philosophy (1687). It proved to be one of the most influential works in the history of science. In its pages Newton asserted the three Laws of Motion, elaborated Johannes Kepler’s Laws of Motion, and stated the Law of Universal Gravitation. The book is primarily a mathematical work, in which Newton developed and applied calculus, the mathematics of change, which allowed him to understand the motion of celestial bodies. To reach his conclusions he also used accurate observations of planetary motion, which he made by designing and building a new kind of telescope, one that used mirrors to reflect, rather than lenses to refract, light. Illustration from The Mathematical Principles of Natural Philosophy by Isaac Newton © CORBIS Newton’s three Laws of Motion are: 01 - Every body continues at rest or in motion in a straight line unless compelled to change by forces impressed upon it. (Galileo first formulated this, and Newton recast it.)02 - Every change of motion is proportional to the force impressed and is made in the direction of the straight line in which that force is impressed. (A planet would continue outward into space but is perfectly balanced by the Sun’s inward pull, which Newton termed “centripetal” force.)03 - To every action there is always opposed an equal reaction, or the mutual action of two bodies on each other is always equal and directed to contrary parts. 01 - Every body continues at rest or in motion in a straight line unless compelled to change by forces impressed upon it. (Galileo first formulated this, and Newton recast it.) 02 - Every change of motion is proportional to the force impressed and is made in the direction of the straight line in which that force is impressed. (A planet would continue outward into space but is perfectly balanced by the Sun’s inward pull, which Newton termed “centripetal” force.) 03 - To every action there is always opposed an equal reaction, or the mutual action of two bodies on each other is always equal and directed to contrary parts. Putting these laws together, Newton was able to state the Law of Universal Gravitation: “Every particle of matter attracts every other particle with a force proportional to the product of the masses of the two particles and inversely proportional to the square of the distance between them.” Stated more simply, the gravitational attraction between two bodies decreases rapidly as the distance between them increases. This calculation proved powerful because it presented the Universe as an endless void filled with small material bodies moving according to harmonious, rational principles. Newton understood gravity as a universal property of all bodies, its force dependent only on the amount of matter contained in each body. Everything, from apples to planets, obeys the same unchanging laws. By combining physics, mathematics, and astronomy, Newton made a giant leap in human understanding of Earth and the cosmos. Newton’s mathematical method for dealing with changing quantities is now called the calculus. Newton did not publish his method but solved problems using it. Later the German scientist Gottfried Wilhelm von Leibniz also worked out “the calculus”, and his notation proved easier to use. Newton accused Leibniz, in a nasty dispute, of stealing his ideas, but historians now believe that each invented the calculus independently. Timeline of Newton's life. Click here for a larger version. Download PDF. Recognition Newton was made a knight by Queen Anne in 1705 and, at his death in 1727, he was buried in London’s Westminster Abbey. He now rests in a place of prominence near the poet Geoffrey Chaucer and the astronomer John Herschel. Shortly before he died, Newton remarked: I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the seashore and diverting myself in now and then finding a smoother pebble or prettier shell than ordinary, while the great ocean of truth lay all undiscovered before me. For Further Discussion Think about the following question and write your response and any additional questions you have in the Questions Area below. How does the Law of Universal Gravitation explain the motion of the planets?​ [Sources and attributions]

The Red Supergiant Betelgeuse The Red Supergiant Betelgeuse. Source: ESO/L. Calcada This is an artist's impression of the red supergiant Betelgeuse in Orion, a prominent constellation throughout the world. Betelgeuse, the 8th brightest star in the night sky, can be easily identified as one of Orion's armpits. Betelgeuse's exact size is hard to calculate but if the star were at the center of our Solar System it would entirely engulf Earth, Venus, and Mars. A Black Hole in Centaurus A A Black Hole in Centaurus A. Source: X-ray: NASA/CXC/CFA/R.Kraft et al.; Submillimeter: MPIfR/ESO/APEX/A.Weiss et al.; Optical: ESO/WFI This image of the galaxy Centaurus A demonstrates the incredible size and power of the supermassive black hole at its center. The X-ray jet in the upper left side of this image is powered by the central black hole and extends outwards for about 13,000 light years from the event horizon. The Basic Structure of a Star The Basic Structure of a Star. Source: ESA/NASA/SOHO and the Big History Project This diagram shows the basic structure of a star like our Sun. Hydrogen is fused in the star's core, forming helium and sometimes heavier elements as the fusion process continues. Incredible amounts of energy are released in the process. Source: ESA/NASA/SOHO and the Big History Project Our Sun and VY Canis Majoris Our Sun and VY Canis Majoris. This is an approximate comparison of the size difference between our Sun and the largest known star, VY Canis Majoris, in the constellation Canis Major. The diameter of VY Canis Majoris is more than 1,800 times that of the Sun. Bear in mind that these two stars are at different stages in their lives, further contributing to the size difference. The Hertzsprung-Russell Diagram The Hertzsprung-Russell Diagram. Source: ESO In the Hertzsprung-Russell Diagram, the luminosities (brightnesses) of stars are plotted against their temperatures. The position of a star in the diagram demonstrates its present stage and its mass. Stars that fuse hydrogen into helium lie on the central diagonal branch, the so-called "main sequence." Red dwarfs like AB Doradus C lie in the cool and faint corner.  When a star exhausts all if its hydrogen, it leaves the main sequence and becomes a red giant or a supergiant, depending on its mass. When medium-sized stars with masses similar to our Sun age, they will swell in size and become red giants. Without enough mass to cause a supernova, they will burn all of their fuel and eventually shrink into white dwarfs (seen in the lower left). An Unstable, Dying Star Called Eta Carinae An Unstable, Dying Star Called Eta Carinae. Source: X-ray: NASA/CXC/GSFC/M. Corcoran et al: Optical: NASA/STScl Eta Carinae is a massive (100-150 solar masses) and unstable star that astronomers expect will end in a supernova. In the 1840s Eta Carinae erupted, ejecting material 10 times the mass of the Sun and briefly becoming the second brightest star in the sky - an early indication of the massive explosion expected to come. The Dying Star Eta Carinae The Dying Star Eta Carinae. Source: Jon Morse (University of Colorado) and NASA In this image of Eta Carinae, the dying star resembles a cancerous tumor or an infected organ. Eta Carinae's final demise is likely to be a supernova that will look as bright as the full Moon. Tycho's Supernova Remnant Tycho's Supernova Remnant. Source: X-ray: NASA/CXC/SAO; Infrared: NASA/JPL-Caltech; Optical: MPIA, Calar Alto, O. Krause et al. This blazing hot cloud of gas and debris in the constellation Cassiopeia, SN 1572 or B Cas, is the remnant of the supernova that Tycho Brahe and other astronomers and stargazers witnessed in November 1572. This bright explosion deep in space demonstrated to astronomers like Brahe that the Universe was alive and in constant motion.

Pure Metal: Jābir Ibn Ḥayyān By Trevor R. Getz Whether an individual or a collection of people, Jābir ibn Ḥayyān’s work with chemical substances was an inspiration and guide for the later creators of chemistry. The original transformer Whether you realize it or not, you wake up every morning and do some chemistry. You might turn the liquids in your eggs into solids. Maybe you remove the moisture inside your bread to make toast. Meanwhile, your parents may be adding hot water to ground-up beans to create new and complex compounds that taste good and give them a caffeine buzz. Chemistry is everywhere. Chemistry is the modern science that deals with the structure and properties of substances and how they are transformed. But modern chemistry didn’t just happen. It grew out of a long history of curious humans who used trial and error to answer questions like: How do you make raw foods edible?How do you turn ash and fat into soap?How do you turn mineral-bearing rocks into iron? Most trials ended in error, but when they succeeded, people passed on the ideas to later generations, which helped expand our collective learning. But these ideas weren’t always studied in a scientific way. Between the days of trial and error and the arrival of modern science was something called alchemy. Not exactly science, and not exactly magic, alchemy mixes religion, spirituality, and experimentation in order to study the properties of natural substances, especially metals. Perhaps the greatest of the alchemists was Jābir ibn Ḥayyān, a Muslim Persian innovator who wrote over 3,000 texts on alchemy. These included: A list—including descriptions—of all the known tools and equipment used by Greek and Muslim alchemistsHistories of the progress made by earlier alchemistsPerhaps most important, studies of the characteristics of different metals You see, ibn Ḥayyān was one of the first people to describe the qualities of different metals, and he had a good reason for doing so. Alchemists wanted to know how you might transform one metal into another. Well, what they really wanted to do was to turn lead, a cheap metal, into gold, an expensive metal. The way to pursue that challenge was to study the qualities of each metal. Then they had to figure out the process by which you might change those qualities. In what may be his most important contribution to later scientists, ibn Ḥayyān began to study how mixing substances—using heat, acid, and other methods and tools—could change them. These processes included: Distillation – Purifying something by boiling it and then capturing the steam.Filtration – Putting a substance through a filter to remove impurities.Amalgamation – Mixing two substances together so they become a new substance. Jābir ibn Ḥayyān’s experiments resulted in achievements that included the isolation of sulfuric acid and nitric acid and the purification of gold and mercury. These experiments were recorded and shared with others, and helped inform future generations of scholars. By BHP and Peter Quatch, CC BY-NC 4.0. In the process of his work with metals, ibn Ḥayyān learned how to purify gold and mercury. He also isolated substances that could be used to transform other metals, including sulfuric acid and nitric acid. A man? Or a school? Who was this brilliant man who wrote 3,000 texts and invented new ways to transform substances? It’s still a mystery. There probably was a man named Jābir ibn Ḥayyān. He was probably born in the city of Tus, in Persia. He probably worked for the Abbasid ruler Harun al-Rashid. And he probably wrote some of the 3,000 texts associated with his name. But it’s likely that a lot of the work that people attach his name to was written by other people living around the same time or later. So, if that’s true, we’re looking at something much more exciting than a single innovator. We’re probably looking at a whole school of alchemists. Many of them were probably students of ibn Ḥayyān’s, working together, sharing notes and ideas, and passing them on. If the 3,000 texts were written by several or many people, then we have evidence of a great effort to understand metals and other substances and transform them. Maybe they all worked together in a laboratory, or workshop. Maybe there was even a whole school of alchemists in one location! From Jābir to Geber to.... And, if it were a school, what an important school it was! The work of Jābir ibn Ḥayyān spread across the Islamic world and was preserved for later researchers—and there’s no “maybe” about that. This work was highly influential. The ibn Ḥayyān texts were translated into Latin, and by the twelfth century, they were found in Spain, Italy, and England. One group of fourteenth-century Spanish experimenters even signed their own work “Geber” to honor the influence of “Jābir.” Later, Sir Isaac Newton studied ibn Ḥayyān, and in his own studies on the nature of matter, he reproduced some of these earlier experiments. Ibn Ḥayyān’s work looked quite different from the work of modern scientists. Yet, like many great innovators before the modern period, ibn Ḥayyān helped pave the way for later scholars who used the scientific method. His work featured many methods that later scientists would adopt. These include some of the first attempts to create a list of qualities that compare one metal to another. He also invented both new tools and new liquids in his ambition to transform one substance into another. Finally, he recorded everything very carefully. Whether he was one man, or a whole school or laboratory of scientists, ibn Ḥayyān represents an important step between the trial and error of everyday work and the carefully recorded and studied science of chemistry. Author bio Trevor Getz is a professor of African History at San Francisco State University. He has written 11 books on African and world history, including Abina and the Important Men. He is also the author of A Primer for Teaching African History, which explores questions about how we should teach the history of Africa in high school and university classes. [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. Reading 1: Skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Reading 2: Understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: What issues did Chandra face when he presented his calculations about the death of stars?What was Chandra's experience at the University of Chicago like?What was Chandra's most important contribution to collective learning?How has the artist designed the images in this comic to help you know in which order to read the text?Looking at just the images, what do you think is the theme of this comic? What issues did Chandra face when he presented his calculations about the death of stars? What was Chandra's experience at the University of Chicago like? What was Chandra's most important contribution to collective learning? How has the artist designed the images in this comic to help you know in which order to read the text? Looking at just the images, what do you think is the theme of this comic? Reading 3: Evaluating and Corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: What does Chandra's experience sharing his ideas about stars teach you about the process of collective learning? His did his theory become accepted? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. The Evolving Star: Subrahmanyan Chandrasekhar - Graphic Biography Writer: Eman M. Elshaikh Artist: Kay Sohini Subrahmanyan Chandrasekhar was an Indian physicist who won the Nobel Prize for Physics. His work gave us tremendous insights into the life and death of stars. Download the Graphic Biography PDF here or click on the image above.

All of the following terms appear in this unit. The terms are arranged here in alphabetical order. carbon — A chemical element with six protons that is the basis for all known life on Earth. chemical element — A substance whose atoms are all the same (that is, each atom contains the same number of protons as each of the other atoms in the substance). Sometimes, the word “element” is used to refer to the atoms or atomic nuclei themselves, as in the statement “Many elements are formed as products of dying stars.” chemistry — The scientific study of the composition, structure, properties, and reactions of different forms of matter. cluster — A group of galaxies held together by their mutual gravitational pulls. cosmic horizon — The distance in our Universe beyond which we cannot see (46-billion to 47-billion light- years from Earth). Light from beyond the cosmic horizon has not yet had enough time (in the history of the Universe) to reach us. density — The mass per unit of volume of a substance. fusion (also called nuclear fusion) — The combining of lighter atomic nuclei into heavier atomic nuclei. This process can release a great deal of energy, and is what powers most stars. galaxy — A huge system of stars, interstellar dust, and dark matter, held together by mutual gravitational pull. ion — An atom that has a different number of protons than electrons, giving it an overall positive or negative charge. iron — A chemical element with 26 protons. The most common chemical element in the planet Earth, iron forms the majority of Earth’s inner and outer core. The process of creating new elements through nuclear fusion in stars ends with iron, since fusing atomic nuclei together to produce elements heavier than iron does not produce energy. Milky Way galaxy — The spiral-shaped galaxy that contains our Solar System. neutron star — One possible end product of supernovae. When a star much more massive than our Sun runs out of fuel, its core may collapse to produce a ball of neutrons more dense than virtually anything else in the Universe. periodicity — Regular, recurring trends. For example, a Cepheid variable star exhibits periodicity because its brightness changes in a regular, predictable way that repeats over time. periodic table of elements — The generally accepted system for organizing the known chemical elements. Russian chemist Dmitri Mendeleev first used this method of arrangement in 1869. As new elements are discovered, they are added to the table. plasma — A state of matter in which protons and electrons are not bound together. This was the state of the entire Universe roughly before 380,000 years after the Big Bang, and is the normal state inside stars. radioactivity — The breakdown of an unstable atomic nucleus, such as uranium, through the spontaneous emission of subatomic particles. star — A huge, glowing ball of plasma held together by its own gravity. Stars, the first complex entities in the Universe, have structure, stability, and a sustained flow of energy due to nuclear fusion at their centers. supercluster — A large group of galaxy clusters that together form some of the largest known structures in the Universe. supernova — The explosion of a large star at the end of its life; most chemical elements are created by supernova explosions.

A Closer Look at the Popular Metal A Greek silver tetradrachm from about 160 BCE © Hoberman Collection/CORBIS By Big History Project It’s amazing how much you can learn when you look at things through the lens of Big History. Take a medium-weight element like silver, a shiny whitish metal with an unassuming spot (atomic number 47) on the periodic table between palladium and cadmium. The value of silver Silver puts the luster in jewelry, helps our cell phones and MP3 players work better, and even makes hospitals safer. Let’s explore the many roles that silver has played throughout history. What makes silver more valuable to us than other minerals? Its beauty is one thing. This attractive and reflective metal has fascinated men and women for a long time. Silver also is fairly scarce — and things that are both beautiful and rare tend to be worth a lot (think diamonds, gold, and masterpieces of art). Silver is very durable, too. And it’s malleable, meaning it’s easy to shape. All these qualities have made silver very useful and valuable to this day. Silver’s monetary value has long been appreciated. Thought to be perhaps the oldest coin, the “Lydian Lion” was minted in modern-day Turkey some 2,700 years ago; early metalworkers — chemists of sorts — made the coins from electrum, an alloy of gold and silver. The Minoan civilization, which flourished on the island of Crete around 2000 BCE, and the Mycenaean people of early mainland Greece imported great amounts of silver mined in ancient Armenia. Transport of the metal between all of these places helped to accelerate trade throughout the Mediterranean region. After the catastrophic destruction of the Minoan civilization in 1600 BCE, and the decline of the Mycenaean culture around 1200 BCE, silver’s prominence continued as production shifted with the rising civilization of Classical Greece. The silver mines of Laurium (near Athens) paid for the Italian lumber used to build the fleets of triremes (warships with three levels of rowers) that made ancient Athens a naval superpower. The Romans would later adopt silver as one of their main currencies as well. Silver helped advance global civilization by connecting East and West through trade. Silver was scarce in China, but nonetheless much valued as currency. So, during the Middle Ages, Europeans used silver to buy Chinese goods — gunpowder, tea, ceramics, and silk — which were then carried over the fabled “Silk Road.” Later, when the Spanish discovered silver mines in Mexico and Peru, they established a sailing route across the Pacific, trading South American silver, some of it plundered, for Chinese silk. Silk was desirable because it made light and cool clothing much in demand by Spanish settlers in the hot, humid climate in parts of Mexico, Central America, and South America. As we’ll see elsewhere in this course, when goods get traded, so do ideas. So silver played a role in advancing collective learning. A 1739 Spanish silver dollar, also called a “piece of eight,” public domain By the 17th century, Mexican “pieces of eight” — also known as “Spanish dollars” — had become the world’s first global currency. The U.S. dollar was based on these coins and for a long time many U.S. coins contained silver. The Latin word for silver is argentum. What South American country sounds like that? Right — Argentina! During the time of the Spanish explorers in the 1500s, Argentina was thought to be rich in what shiny metal element? Silver, of course. ​The many uses of silver Silver also has strong antibacterial properties that have been acknowledged for millennia. The ancient Greek physician Hippocrates, sometimes called the “father of medicine,” wrote of silver’s healing properties, and early records indicate that the Phoenicians used silver vessels to keep water, wine, and vinegar pure during their long voyages at sea. You may have heard the phrase “born with a silver spoon in your mouth.” That’s not necessarily about being rich. In the 18th century, babies fed with silver spoons were thought to be healthier than those fed with spoons made from wood or other materials. Today many hospitals fight infections with equipment that is embedded with silver. Silver is even used in the thread of some socks. Why? The silver kills bacteria that make the socks smell bad! Silver is the best metallic conductor of electricity, better than copper or gold. That’s why so many electronics, like your computer keyboard or music player, rely on it. Alloys of silver are used in dentistry, photography, even in the operation of nuclear power plants. Silver also helps keep airplanes aloft. Because of its poor coefficient of friction (meaning, it’s slippery!), silver is used to coat the ball bearings used in jet engines. But did you know that billions of years ago there was no silver anywhere in the Universe? So where did it come from? Like most other elements in the periodic table, silver was created in dying stars — and in the cataclysmic supernova explosions that sometimes marked their final demise. This is the only place where temperatures get hot enough to fuse hydrogen nuclei together to form larger atoms. These larger, heavier atoms eventually went on to help form planets like Earth. So in a sense, silver, like everything else around you, was made from the first atoms of hydrogen. Where and when was hydrogen created? In the Big Bang itself. It turns out silver has a pretty big history! For Further Discussion Think about how the properties and location of chemical elements such as silver impact our lives today. What would be different if silver were as plentiful as carbon?What would it mean if silver were only found in one place on the planet? What would be different if silver were as plentiful as carbon? What would it mean if silver were only found in one place on the planet? Share your answer to one of these questions in the Questions Area below. [Sources and attributions]

Marie Curie: Chemistry, Physics, and Radioactivity Marie Curie in 1898 © Bettmann/CORBIS By Michele Feder Using a makeshift workspace, Marie Curie began, in 1897, a series of experiments that would pioneer the science of radioactivity, change the world of medicine, and increase our understanding of the structure of the atom. Early Life and Overcoming Obstacles Marie Curie became famous for the work she did in Paris. But she was born in Warsaw, Poland, in 1867, as Maria Sklodowska. She was the youngest of five children, and both of her parents were educators: Her father taught math and physics, and her mother was headmistress of a private school for girls. Circumstances changed for Maria’s family the year she turned 10. Her mother died, and her father lost his job. Her father rented bedrooms to boarders, and Maria had to sleep on the floor. Even as a young girl, Maria was interested in science. Her father kept scientific instruments at home in a glass cabinet, and she was fascinated by them. Maria proved herself early as an exceptional student. At that time, Russia ruled Poland, and children had to speak Russian at school; indeed, it was against the law to teach Polish history or the Polish language. Nevertheless, Maria graduated from high school when she was 15 with top grades. She wanted to continue her education in physics and math, but it would be decades before the University of Warsaw admitted women. Maria knew she would have to leave Poland to further her studies, and she would have to earn money to make the move. Maria’s sister Bronya, meanwhile, wanted to study medicine. Together, they made a deal: Maria would work to help pay for Bronya’s medical studies. Then, when Bronya was a doctor, she would help pay for Maria’s education. When Maria’s turn came, she did not want to leave her family or country, but knew it was necessary. She chose Paris because she wanted to attend the great university there: the University of Paris — the Sorbonne — where she would have the chance to learn from many of the era’s leading thinkers. In Paris When Maria registered at the Sorbonne, she signed her name as “Marie,” and worked hard to learn French. Of 1,800 students there, only 23 were women. Many people still believed that women should not be studying science, but Marie was a dedicated student. She rented a small space in an attic and often studied late into the night. In 1893, Marie took an exam to get her degree in physics, a branch of science that studies natural laws, and passed, with the highest marks in her class. She was the first woman to earn a degree in physics from the Sorbonne. Marie thought seriously about returning to Poland and getting a job as a teacher there. But she met a French scientist named Pierre Curie, and on July 26, 1895, they were married. They rented a small apartment in Paris, where Pierre earned a modest living as a college professor, and Marie continued her studies at the Sorbonne. In September 1897, Marie gave birth to a daughter, Irène. Meanwhile, scientists all over the world were making dramatic discoveries. The year the Curies were married, a German scientist named Wilhelm Roentgen discovered what he called “X-radiation” (X-rays), the electromagnetic radiation released from some chemical materials under certain conditions. This breakthrough served as a catalyst for Marie’s own work. Other scientists began experimenting with X-rays, which could pass through solid materials. While researching the source of X-rays, French physicist Antoine Henri Becquerel found that uranium gave off an entirely new form of invisible ray, a narrow beam of energy. Marie Curie wanted to know why. One of her greatest achievements was solving this mystery. Radiant Discoveries Marie Curie, and other scientists of her time, knew that everything in nature is made up of elements. Elements are materials that can’t be broken down into other substances, such as gold, uranium, and oxygen. When Marie was born, there were only 63 known elements. (Today 118 elements have been identified.) At the time she began her work, scientists thought they had found all the elements that existed. But they were wrong. Marie began testing various kinds of natural materials. One substance was a mineral called “pitchblende.” Scientists believed it was made up mainly of oxygen and uranium. But Marie’s tests showed that pitchblende produced much stronger X-rays than those two elements did alone. She began to think there must be an undiscovered element in pitchblende that made it so powerful. Marie Curie in her laboratory © Hulton-Deutsch Collection/CORBIS To prove it, she needed loads of pitchblende to run tests on the material and a lab to test it in. Pierre helped her find an unused shed behind the Sorbonne’s School of Physics and Chemistry. There, Marie put the pitchblende in huge pots, stirred and cooked it, and ground it into powder. She added chemicals to the substance and tried to isolate all the elements in it. Every day she mixed a boiling mass with a heavy iron rod nearly as large as herself. After months of this tiring work, Marie and Pierre found what they were looking for. In 1898, Marie discovered a new element that was 400 times more radioactive than any other. They named it “polonium,” after her native country. Later that year, the Curies announced the existence of another element they called “radium,” from the Latin word for “ray.” It gave off 900 times more radiation than polonium. Marie also came up with a new term to define this property of matter: “radioactive.” It took the Curies four laborious years to separate a small amount of radium from the pitchblende. In 1902, the Curies finally could see what they had discovered. Inside the dusty shed, the Curies watched its silvery-blue-green glow. Marie later remembered this vividly: “One of our pleasures was to enter our workshop at night. Then, all around us, we would see the luminous silhouettes of the beakers and capsules that contained our products.” (Santella, 2001) Marie presented her findings to her professors. She suggested that the powerful rays, or energy, the polonium and radium gave off were actually particles from tiny atoms that were disintegrating inside the elements. Marie’s findings contradicted the widely held belief that atoms were solid and unchanging. Originally, scientists thought the most significant learning about radioactivity was in detecting new types of atoms. But the Curies’ research showed that the rays weren’t just energy released from a material’s surface, but from deep within the atoms. This discovery was an important step along the path to understanding the structure of the atom. A Woman of Distinction In 1903, Marie received her doctorate degree in physics, which was the first PhD awarded to a woman in France. In November of the same year, Pierre was nominated for the Nobel Prize, but without Marie. He sent a letter to the nominating committee expressing a wish to be considered together with her. For their discovery of radioactivity, the couple, along with Henri Becquerel, shared the Nobel Prize in physics. Marie Curie was the first woman to receive a Nobel Prize. After many years of hard work and struggle, the Curies had achieved great renown. But there was one serious problem. The Curies were unable to travel to Sweden to accept the Nobel Prize because they were sick. Both of them suffered from what later was recognized as radiation sickness. Marie coughed and lost weight; they both had severe burns on their hands and tired very quickly. All of this came from handling radioactive material. At the time, scientists didn’t know the dangers of radioactivity. The Nobel (accepted on the Curies’ behalf by a French official in Stockholm) contributed to a better life for the couple: Pierre became a professor at the Sorbonne, and Marie became a teacher at a women’s college. (The Sorbonne still did not allow women professors.) The prize itself included a sum of money, some of which Marie used to help support poor students from Poland. In 1904, Marie gave birth to Eve, the couple’s second daughter. Around that time, the Sorbonne gave the Curies a new laboratory to work in. But on April 19, 1906, this period came to a tragic end. On a busy street, Pierre Curie was hit by a horse-drawn carriage. He died instantly. Only 39 years old when she was widowed, Marie lost her partner in work and life. Marie struggled to recover from the death of her husband, and to continue his laboratory work and teaching. Though the university did not offer her his teaching job immediately, it soon realized she was the only one who could take her husband’s place. On November 5, 1906, as the first female professor in the Sorbonne’s history, Marie Curie stepped up to the podium and picked up where Pierre had left off. Around her, a new age of science had emerged. A Chemistry of the Invisible An atom is the smallest particle of an element that still has all the properties of the element. Periodic table creator Dmitri Mendeleev and other scientists had insisted that the atom was the smallest unit in matter, but the English physicist J. J. Thompson, responding to X-ray research, concluded that certain rays were made up of particles even smaller than atoms. The work of Thompson and Curie contributed to the work of New Zealand–born British scientist Ernest Rutherford, a Thompson protégé who, in 1899, distinguished two different kinds of particles emanating from radioactive substances: “beta” rays, which traveled nearly at the speed of light and could penetrate thick barriers, and the slower, heavier “alpha” rays. Marie considered radioactivity an atomic property, linked to something happening inside the atom itself. Rutherford, working with radioactive materials generously supplied by Marie, researched his “transformation” theory, which claimed that radioactive elements break down and actually decay into other elements, sending off alpha and beta rays. The Curies had resisted the decay theory at first but eventually came around to Rutherford’s perspective. It confirmed Marie’s theory that radioactivity was a subatomic property. ​In 1904, Rutherford came up with the term “half-life,” which refers to the amount of time it takes one-half of an unstable element to change into another element or a different form of itself. This would later prove an important discovery for radiometric dating when scientists realized they could use “half-lives” of certain elements to measure the age of certain materials. In 1905, an amateur Swiss physicist, Albert Einstein, was also studying unstable elements. According to his calculation very small amounts of mat- ter were capable of turning into huge amounts of energy, a premise that would lead to his General Theory of Relativity a decade later. In 1906, Marie voiced her acceptance of Rutherford’s decay theory. By then, Thompson was calling the particles smaller than atoms “electrons,” the first subatomic particles to be identified. Thompson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron and for his work on the conduction of electricity in gases. In 1911, Rutherford made another breakthrough, building upon Thompson’s earlier theory about the structure of the atom. He outlined a new model for the atom: mostly empty space, with a dense “nucleus” in the center containing “protons.” Marie’s isolation of radium had provided the key that opened the door to this area of knowledge. She had created what she called “a chemistry of the invisible.” The age of nuclear physics had begun. Timeline of Curie's life. Click here for a larger version. Download PDF. A Second Nobel Prize In the years after Pierre’s death, Marie juggled her responsibilities and roles as a single mother, professor, and esteemed researcher. She wanted to learn more about the elements she discovered and figure out where they fit into Mendeleev’s table of the elements, now referred to as the “periodic table.” Elements on the table are arranged by weight. To determine the locations for polonium and radium, she needed to figure out their molecular weight. Her research showed that polonium should be number 84 and radium should be 88. In 1911, Marie was awarded the Nobel Prize for Chemistry, becoming the first person to win two Nobel Prizes. This time, she traveled to accept the award in Sweden, along with her daughters. Marie was recognized for her work isolating pure radium, which she had done through chemical processes. A year later, Marie was visited by Albert Einstein and his family. The two scientists had much to discuss: What was the source of this immense energy that came from radioactive elements? To promote continued research on radioactivity, Marie established the Radium Institute, a leading research center in Paris and later in Warsaw, with Marie serving as director from 1914 until her death in 1934. Marie Curie’s radioactivity research indelibly influenced the field of medicine. In 1904, the first textbook that described radium treatments for cancer patients was published. During World War I, she designed radiology cars bringing X-ray machines to hospitals for soldiers wounded in battle. She also equipped and staffed 200 permanent radiology posts in hospitals. Marie trained women as well as men to be radiologists. In the last two years of the war, more than a million soldiers were X-rayed and many were saved. Her research laid the foundation for the field of radiotherapy (not to be confused with chemotherapy), which uses ionizing radiation to destroy cancerous tumors in the body. Marie Curie died of a type of leukemia, and we now know that radioactivity caused many of her health problems. In the 1920s scientists became aware of the dangers of radiation exposure: The energy of the rays speeds through the skin, slams into the molecules of cells, and can harm or even destroy them. Marie Curie in her laboratory in 1905 © Bettmann/CORBIS A Place in the Periodic Table In 1944, scientists at the University of California–Berkeley discovered a new element, 96, and named it “curium,” in honor of Marie and Pierre. Today we recognize 118 elements, 92 formed in nature and the others created artificially in labs. Marie Curie’s legacy cannot be overstated. Poverty didn’t stop her from pursuing an advanced education. Marriage enhanced her life and career, and motherhood didn’t limit her life’s work. At a time when men dominated science and women didn’t have the right to vote, Marie Curie proved herself a pioneering scientist in chemistry and physics. By Michelle Feder For Further Discussion What are some of the key differences between the experience of Marie Curie and other scientists? Did her experience help or hinder her progress? In the Questions Area below, in just a few sentences, provide an explanation for why you think her experiences either helped or hindered her progress. Or, constructively agree or disagree with someone else’s answer. [Sources and attributions]

First-Hand Plate Tectonics Kawah Ljen crater lake, Java, Indonesia © Philippe Crochet/Photononstop/Corbis "I was squinting into the bright sunlight reflecting off the glacier, and my friend ray, the photographer, walked a short ways ahead, a tall silhouette against the brilliant snow and ice." Writer Peter Stark (right) and guide, Olifur, survey the Icelandic landscape near the Mid-Atlantic Ridge. © Raymond Geyman The wind blew so hard it made us stagger and the gale’s force bowed the rope that linked the two of us and the guide ahead like a giant strand of spaghetti. A reddish ridge of earth protruded from the glacier and puffs of steam swirled and kicked from its far side. We were now nearing the place where fire mingled with ice. All of sudden Ray disappeared. He vanished so quickly I couldn’t understand what had happened, as if a magician had touched him with a wand. Puzzled, I looked again ahead of me along the rope. I realized he hadn’t entirely disappeared. Rather, Ray had suddenly become really short. Only his head and shoulders poked above the glacier’s shimmering surface. I now understood that he’d fallen into a crevasse. His legs dangled underneath him in a deep crack in the glacier that probably dropped far down toward volcanic depths below. “Ray!” I shouted, as the wind ripped away my words. “Climb out!” I’m an adventure writer. Magazines send me to wild and faraway places. When a magazine asked me to write an article about Iceland, I jumped at the chance and invited Ray along to take photos. While planning the trip, I learned that Iceland is known as the land of “fire and ice” because it’s dotted with big glaciers and live volcanoes. Far in the center of the island, the fire and ice — the glaciers and volcanoes — mix together in dramatic and sometimes explosive fashion. Getting to that spot became the goal of our trip. That journey would change the way I think about our planet Earth. An adventurer negotiates a crevasse on the Hofsjokull Glacier in central Iceland. © Christopher Herwig/Aurora Photos/Corbis As you may know, the Earth is a ball of hot, molten rock and minerals covered by the thin outer “crust” of cooled rock on which we live. Giant “plates” of this cooled crust float like rafts or islands over the molten ball of the Earth’s interior. In perpetual — but very slow — motion, most of the plates move only about one inch per year. (In other words, we’re all lava surfing...very, very slowly.) But where they meet along the plate edges, all sorts of crazy things occur. The huge plates scrape past each other sideways. They dive under each other. And in places the constantly moving plates get snagged on each other causing tremendous pressures to build. When this tension suddenly releases, things happen way, way, way faster than one inch per year. My travels have led me to those plate edges in different parts of the world. Some of the bizarre phenomena I’ve witnessed are similar to what scientists observed and experienced during the last century in formulating the theory of plate tectonics. A neckalce of islands Before going to Iceland, I’d spent some time in Indonesia. When I looked at a map of that country, I noticed its hundreds of islands strung out like a 3,000-mile-long necklace of pearls draped in the ocean below Asia. I wondered: “Why is it shaped in such a perfect arc?” Early morning at the Mount Bromo volcano, East Java, Indonesia © DARREN WHITESIDE/Reuters/Corbis Eruption of the Ibu volcano, Halmahera, Indonesia © Martin Rietze/Westend61/Corbis I hadn’t been there long when I started to get an answer. My wife, Amy, and her father, Rags, and I were staying in a little hotel on the Indonesian island of Bali and eating dinner one evening beside the small swimming pool. I looked up from my plate of rice and fish and my mango smoothie and noticed that the water in the swimming pool was sloshing back and forth, as it does when you slide around in a very full bathtub. But no one was in the pool! “I think we’re having an earthquake,” I remarked. “No we’re not,” they replied. The motion was almost too subtle to feel. But when I pointed to the pool, they finally believed me. Earthquakes strike that island necklace of Indonesia almost constantly — usually they are small and subtle, but occasionally huge quakes, including massive undersea tremors that trigger tsunamis, occur as well. I found more evidence of what might be happening with that Indonesian island arc when we climbed a volcano, called Mount Marapi, on the island of Sumatra. Few people climb this volcano. It was difficult to see from below just how active it might be above. We hired a young man from a nearby village who could lead us to the top. Off we went in the rainy darkness before dawn, clambering for hours through dripping, misty rainforest. Finally, the green rainforest ended and we topped out at nearly 10,000 feet on the broad, ashy-gray summit that looked like the surface of the Moon and was scattered with big gray boulders. The guide led us across the top, its flat, ashy surface gently pocked by that morning’s raindrops, until we reached the center. A true-color satellite image of Iceland captured, January 2004, courtesy of Jeff Schmaltz, MODIS Land Rapid Response Team at NASA GSFC A map showing how the island straddles the North American and Eurasian plates. The Mid-Atlantic Ridge in Iceland,U.S. Geological Survey. "Take care," the guide said, and pointed over an edge. We inched closer and poked our heads over. There was the most incredible hole in the Earth I'd ever seen, as wide across as several soccer fields and impossibly deep, falling far away to a bottom I couldn't see. Every 20 or 30 seconds a huge gray huffy blast of foul-smelling smoke and steam and ash came belching out of that rocky shaft and billowed past our faces into the sky. It made me dizzy to look over the rim. Then I looked back around me at the big boulders lying on the summit plateau. I had assumed they'd lain there for years, if not centuries, since the last big eruption. I now noticed that they'd made craters in the ash, disturbing the rain-pocked surface. Right then I realized that the volcano had erupted just since that morning with its lava bombs falling out of the sky onto the summit. It was more than active - it was really active - and it felt like we were standing beside a direct hole down to the molten interior of the Earth. "This thing could erupt again at any moment!" I said to Amy. "Let's get out of here!" Earth's often violent history This got me interested in knowing more about plate tectonics, the theory that scientists developed after observing seismic events like volcanos and earthquakes, studying data like the fossil record, and minutely examining maps. Maps tell amazing stories of the Earth's dynamic and often-violent history, and plate tectonics is a kind of language to read the stories hidden in maps. When I studied a relief map of Indonesia that showed mountains and valleys on land and undersea, I noticed a huge ocean "trench" - the deepest underwater valley you can imagine. nearly five miles deep - running alongside the island necklace. Why that arcing trench? Plate tectonics taught me that Indonesia's necklace of islands traces a distinct seam in the Earth's crust where two huge plates collide. The Australian Plate is shoving northward at five centimeters per year and diving beneath — subducting — under the Eurasian Plate. This diving creates a deep crease in the Earth’s crust, the Sunda Trench. As the Australian Plate dives and melts into the Earth’s interior, it allows lava to well up to the surface in a necklace of active volcanoes along the seam, one of them the belching vent of our Mount Marapi. You can imagine how that the incredible pressure of two plates colliding shakes Indonesia with near-constant earthquakes, small and large, and occasional mega-quakes, like the 2004 undersea quake and tsunami off Sumatra. A village in Sumatra photographed from a relief helicopter, U.S. Navy photographer Philip A. McDaniel The 2004 Indian Ocean Tsunami​​1250KM  - Length of rupture along the tectonic plate boundary150KM - Width of rupture725 KM/H - Speed of waves during tsunami15 M - Top height of waves475 megatons of TNT - Energy equivalent of that released by the Sumatra-Andaman earthquake that caused the tsunami The 2004 Indian Ocean Tsunami Data: Australian Bureau of Meteorology, U.S. Geological Survey Diving plates also shove up mountain ranges from below, like shoving a spatula under a sheet of raw pie dough, which is why Mount Everest, already at 29,035 feet the world’s tallest mountain, grows an inch or two taller every year. Sometimes I try to imagine what the plates are doing directly under my feet. This is something you can do, wherever you live. Centers of continents, like the center of a raft, tend to be more stable than a subduction zone on a coast. But not always. I live with my family in the interior of the North American Plate, in Missoula, Montana. This is not so far from Yellowstone Park. All those famous geysers are actually boiling up from a “hot spot” where a massive bubble of lava pushes close to the Earth’s surface from deep beneath the crust and boils water that’s flowing underground. The North American Plate is sliding over that huge lava dome. (I’m lava surfing even while I’m writing this.) Over millions of years, as the Rocky Mountains slid over the Yellowstone Hot Spot, it melted and crumbled a wide channel right through the mountain ranges, like a hot pan melting lumps of butter, and snow and rain flowed off the Rockies into the channel to form a river. This channel both helped and nearly killed early European explorers of the West. Trying to find a pass through the Rocky Mountains to reach the Pacific Ocean, they got funneled into this channel — today called the Snake River Valley — and paddled their canoes down its river. Too late, they discovered that the river eventually left the channel and flowed straight into an ancient ocean trench, now on dry land, created by the Pacific Plate diving under the North American Plate and then cut deeper by the river. Huge rapids smashed the explorers’ canoes and trapped them in the canyon bottom. Here they nearly starved to death. Fire and ice The explorers had stumbled into the deepest canyon in North America — a mile and a half deep, far deeper than the Grand Canyon — which they called “The Devil’s Scuttlehole” and today is known as Hells Canyon of the Snake River. (The stunt rider Evel Knievel brought notoriety to a nearby section of the Snake River Canyon when he tried to jump it on his rocket-powered motorcycle, didn’t make the gap, fell out of the sky, and landed by parachute in the canyon bottom.) "The deepest canyon in North America was called “The Devil’s Scuttlehole.” Today it’s known as Hells Canyon." Emerald Pool at Yellowstone National Park, Wyoming © Rachael Schumacher The Yellowstone River at Yellowstone National Park, Wyoming © Don Johnston/All Canada Photos/Corbis Iceland, where I traveled with Ray, is almost the opposite of a subduction zone of the type that formed Hells Canyon and the Rocky Mountains. I learned Iceland sits directly atop a giant seam where two plates are not colliding or diving but spreading apart. Known as the Mid-Atlantic Ridge, here lava wells between two plates adding to their edges and creating a string of undersea volcanoes. Iceland is where some of the volcanoes rise above the Atlantic Ocean but it lies so near the North Pole that glaciers cover parts of it. Thus our goal: to reach a spot where volcanic fire mingled with glacial ice. That’s where Ray was dangling in an icy crevasse. Fortunately, Ray carried a pair of skis in his arms. The skis and the rope tied to his waist snagged on the crevasse’s lip and prevented him from falling farther down into the crack. He quickly pulled himself out before the guide and I had to rescue him. We staggered onward into gale and into ice crystals pelting our faces. "It looked like another planet extending in the distance — rippled plains of lava, a strip of desert where sand and dust blew." Peter Stark’s expedition looks out from atop the Mid-Atlantic Ridge © Raymond Geyman Finally we stepped off the glacial ice and onto the reddish ridge. We clambered up it. From the top, there was a spectacular sight. It looked like another planet extending in the far distance — rippled plains of solidified lava, a strip of desert where sand and dust blew in the gale, huge glacial sheets, distant mountains. At our feet, below us, lay a small blue lake sparkling in the sun surrounded by hillsides of reddish earth and patches of glacial ice. Everywhere around the lake steam sprung from the Earth — from the hillsides, from the shores, from steaming vents in the glacier itself. We’d arrived at the spot where fire mixes with ice. We now stood directly atop the Mid-Atlantic Ridge. Here, the Earth was new. By Peter Stark For Further Discussion If we are all lava surfers, why do some parts of the Earth have relatively “small waves,” but other places, like Indonesia, have “big waves”? Share your answers in the Questions Area below! [Sources and attributions]

The Universe Through a Pinhole: Hasan Ibn al-Haytham By Bennett Sherry Hasan Ibn al-Haytham revolutionized our understanding of how light moves through the Universe and how we see it. He urged people to question ancient knowledge. Standing on the shoulders of giants...and yelling in their ear Isaac Newton said he saw further because he stood on the shoulders of giants, but historians have often ignored just how true this was. Newton’s understanding of his actual ability to see, and to comprehend the things he saw, was thanks in part to one invisible giant: Hasan Ibn al-Haytham. Our understanding of the Universe—of the stars and celestial bodies that travel across the night sky—depends on our ability to see light. Once scientists understood how light moves and how it reaches us, so many new discoveries were possible. For example, one of the most important advances in the study of physics was the invention of the telescope. But the telescope was only made possible by an understanding of the science behind light and how we see it, a science called optics. Ibn al-Haytham’s most important book was Kitab al-Manazir, which is Arabic for The Book of Optics. This book explained how the human eye works and how we see objects, such as stars, that are very far away. After Ibn al-Haytham’s book was translated from Arabic into Latin around 1200 CE, it sparked a revolution in optics in Europe. His knowledge provided the basis for many of the great scientific discoveries of later scholars such as Galileo and Kepler. That’s impressive, but what makes Ibn al-Haytham special was how he approached science. He also stood on the shoulders of giants, but he didn’t just stand there. He learned from the knowledge of Greek scholars like Euclid, Aristotle, and Ptolemy, but he also challenged their ideas. To challenge the ancient ideas of these giants, Ibn al-Haytham used the scientific method—and this was 500 years before the Scientific Revolution. The scientific method is the process of asking a question, developing a hypothesis, and testing that hypothesis through rigorous experiments. By using this method, long before it was widely accepted, al-Haytham became one of the giants himself. The Universe through a pinhole Ibn al-Haytham was born in 965 CE in the city of Basra (in present-day Iraq). This part of the world was a center of science and learning at the time. In Basra, Ibn al-Haytham became famous for his mathematical ability. But the young man was perhaps too confident. He claimed that he could build a dam to control the flooding of the great Nile River. When the ruler of Egypt heard of Ibn al-Haytham’s claim, he was very interested in bringing it to life, and invited Ibn al-Haytham to Cairo. Yet, once Ibn al-Haytham stood on the banks of the Nile, he realized his mistake. There was no way he could build a dam large enough. The ruler of Egypt was angered, and Ibn al-Haytham spent the next years either in hiding or imprisoned in his house. But all was not lost. Ibn al-Haytham’s time in isolation helped him see the world in a different light—literally. One night, sitting in a dark room, he noticed moonlight passing through a tiny hole in the wall. Where the light hit the wall on the other side of the room, an image of the Moon was projected. But it was upside down! Why? This question led Ibn al-Haytham to launch a series of experiments to verify a theory he had formed, based on his observation. He reproduced the effect he had seen in the moonlight by building a camera obscura (see Figure 1) and documenting his observations. These observations seemed to have certain patterns, and Ibn al-Haytham developed mathematical explanations for these patterns. Some ancient philosophers believed that human eyes could shoot rays of light outward in a cone, and that when these rays hit objects, we could see them. Ibn al-Haytham was suspicious of this idea and challenged it. This challenge was a big deal—people respected ancient ideas, and many assumed them to be true. Although Ibn al-Haytham might have respected these ancient thinkers too, he wasn’t willing to accept their theories without testing them first. He took the theories of scholars like Euclid, Ptolemy, Galen, and Aristotle and combined them with newer ideas from Arab thinkers. By challenging and improving on these ideas, he developed new theories of light and sight. He backed up his theories with repeated testing and verification, an aspect of the scientific method that scientists still practice today. Changing how we see the way we see Ibn al-Haytham’s big claim was that humans see things because rays of light reflect off of objects in straight lines that then travel to our eyes. That’s probably something you’ve already learned, but without the work of Ibn al-Haytham, you might have been taught that we’re able to see because our eyes shoot beams of light! Fun to think about, but 100 percent mistaken! At the time, and for centuries to come, Ibn al-Haytham’s ideas were revolutionary. His observations in that dark room also allowed him to mathematically prove that the Moon appears bright because of sunlight reflecting off of it. These observations led him to understand that our eyes are connected to our brain by optical nerves (see Figure 2). His work on optics allowed later scientists to stand on his shoulders as they developed innovations like telescopes, microscopes, cameras, and eyeglasses. His dozens of books and his experiments helped other scientists better understand how we perceive objects in the night sky. There’s even a crater on the Moon named after him! Some historians consider Ibn al-Haytham the first scientist because of his rigorous processes for proposing and then testing theories. He used this method in his own work and encouraged others to do so in his books. He wrote: "The seeker after truth is not one who studies the writings of the ancients...and puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them... Thus the duty of the man who investigates the writings of scientists, if learning the truth is his goal, is to make himself an enemy of all that he reads, and, applying his mind to the core and margins of its content, attack it from every side." In this quote, Ibn al-Haytham is urging other scientists to use the scientific method. In other words, we shouldn’t trust old ideas. We should make ourselves “an enemy” of everything we read: always questioning, always testing. Thanks to the work done by Ibn al-Haytham in the tenth and eleventh centuries, later scholars in the Islamic world and Europe—including Isaac Newton—were able to develop new theories about gravity and the movement of stars and planets. The Camera ObscuraCamera obscura is a Latin phrase meaning “dark chamber.” When the light of the Moon passed through a small hole into Ibn al-Haytham’s dark room, it produced an effect that humans have known about and been experimenting with since at least the fourth century in ancient Greece and China. Ibn al-Haytham wanted to know why the projection produced an upside-down image. This effect helped him understand that light moves in straight lines. When light is reflected off an object, it travels in straight lines away from the object in all directions. So, for example, when that light reflecting from the top of an object hits a tiny opening, like the hole in Ibn al-Haytham’s room, it must travel in a straight line. So, it can only land at the bottom of the room. Likewise, light reflecting off the bottom of the object can only land at the top of the room. That’s why the Moon appeared upside down on his wall. The camera obscura. By BHP and Peter Quatch, CC BY-NC 4.0. The Camera Obscura Camera obscura is a Latin phrase meaning “dark chamber.” When the light of the Moon passed through a small hole into Ibn al-Haytham’s dark room, it produced an effect that humans have known about and been experimenting with since at least the fourth century in ancient Greece and China. Ibn al-Haytham wanted to know why the projection produced an upside-down image. This effect helped him understand that light moves in straight lines. When light is reflected off an object, it travels in straight lines away from the object in all directions. So, for example, when that light reflecting from the top of an object hits a tiny opening, like the hole in Ibn al-Haytham’s room, it must travel in a straight line. So, it can only land at the bottom of the room. Likewise, light reflecting off the bottom of the object can only land at the top of the room. That’s why the Moon appeared upside down on his wall. The camera obscura. By BHP and Peter Quatch, CC BY-NC 4.0. Book of OpticsAmong his many contributions to human knowledge, Ibn al-Haytham changed the way we “see” how eyesight actually works. By observing the behavior of light in the camera obscura, he was able to understand that something similar must happen in our eyes. And indeed, he was correct! As light passes through the tiny opening in our eye—the pupil—it creates an upside-down projection on the back of our eye. This revelation led Ibn al-Haytham to another: he was the first to argue that vision happens in the brain, not the eyes. Our brain reinterprets the upside-down projection of light, so we see things right-side-up. His book included detailed diagrams, including the one you see him drawing here, which labeled the different parts of the eye and showed the pathways of the optical nerves.The Book of Optics. By BHP and Peter Quatch, CC BY-NC 4.0. Book of Optics Among his many contributions to human knowledge, Ibn al-Haytham changed the way we “see” how eyesight actually works. By observing the behavior of light in the camera obscura, he was able to understand that something similar must happen in our eyes. And indeed, he was correct! As light passes through the tiny opening in our eye—the pupil—it creates an upside-down projection on the back of our eye. This revelation led Ibn al-Haytham to another: he was the first to argue that vision happens in the brain, not the eyes. Our brain reinterprets the upside-down projection of light, so we see things right-side-up. His book included detailed diagrams, including the one you see him drawing here, which labeled the different parts of the eye and showed the pathways of the optical nerves. The Book of Optics. By BHP and Peter Quatch, CC BY-NC 4.0. Author bio Bennett Sherry holds a PhD in history from the University of Pittsburgh and has undergraduate teaching experience in world history, human rights, and the Middle East. Bennett writes about refugees and international organizations in the twentieth century. He is one of the historians working on the OER Project courses. [Sources and attributions]

The features and physical processes of the Earth. The Andes © Maria Stenzel/National Geographic Society/Corbis The Andes are the longest continental mountain range in the world, stretching about 7,000 km or 4,300 miles from the tip of Chile in the South to Ecuador, Columbia and Venezuela in the north. The highest peak in the Andes is Mt. Aconcagua (6,962 m/22,841 ft.) in Argentina. The Andes range contains numerous high plateau regions and helps feed  the Amazon River, the world's largest river by volume. Folded Rock Francois Gohier / Photo Researchers, Inc. In this image of folded strata in the Andes north of Quito, Ecuador, the geologic processes that formed the mountains are clearly visible. When the oceanic crust of the Nazca plate "subducted" under the South American plate, the lighter continental crust crumpled and continued to push upwards, eventually forming the snow-capped Andes. The Himalayas © Olivier Matthys/epa/Corbis Plate tectonics can also make mountains. Earth's biggest mountain range, the Himalayas formed when the India land mass (atop the Indian plate) slammed into the Eurasian plate. This slow motion collision happened about 50 million years ago, thrusting earth and stone skyward and forming many of the planet's highest mountains, including Mount Everest (8,848 m/29,029 ft.). Seen here are the Karakoram Mountains, a part of the Himalayas that spans the borders between Pakistan, India and China and includes K2 (8,611 m/28,251 ft.), the second highest peak in the world. Differentiation The Big History Project In the early days of Earth, a process called differentiation separated our planet into distinct layers. Density was the key here. Heavier, denser metals like iron and nickel formed the Earth's core while the extremely tightly-packed rocky mantle (some of it molten) surrounded the core. The layer of lighter rock at the Earth's surface is called the crust. It's important to remember that the formation process and ongoing activity created areas where different materials mix, such as veins of metal that reach to the Earth's surface and volcanoes that pump molten lava from the Earth's mantle, sending ash and carbon dioxide into the atmosphere, Earth's outer, gaseous layer. The Earth's Layers The Earth's iron-nickel inner core is hotter than the surface of the Sun but intense pressure makes it solid metal. Molten metal in the outer core generates the Earth's magnetic field and the intense heat sends convection currents into the rocky mantle. These currents, or seismic waves, move through the mantle, causing the movement of the Earth's tectonic plates. The crust, a relatively thin layer around the Earth (think of an apple skin), is composed primarily of basalt (in the oceanic crust) and granite (in the continental crust). The Andes from Space Jeff Schmaltz and NASA In this image of the southern tip of South America, the snow-capped Andes Mountains are clearly visible along the western side of the continent. These mountains were formed when the heavieroceanic crust of the Nazca plate slipped under the South American plate, pushing the lighter continental crust upwards. As oceanic crust is pressed downward into the Earth's mantle, the "subduction zone" becomes a geologically active region, prone to both volcanoes and earthquakes. Plate Tectonics USGS Wegener’s idea that the continents had moved was not accepted by the scientific community until more evidence was found. Geologist and naval officer Harry Hess used sonar readings of the ocean floor, some taken during World War II, to demonstrate "seafloor spreading," helping to cement the modern theory of plate tectonics. Now scientists know that the Earth’s crust consists of several interacting plates that fit together like a jigsaw puzzle. There can be intense pressure where two or more plates meet and these "plate boundaries" are responsible for most of the earthquakes and volcanoes on Earth. Sarychev Peak Eruption in the Ring of Fire Image Science & Analysis Laboratory, Johnson Space Center/NASA This volcano in the Kuril Islands, northeast of Japan, is one of the many active volcanoes in the "Ring of Fire." Shown here in the early stages of a June 12, 2009 eruption, Sarychev Peak is one of many volcanoes along the edge of the Pacific plate.  Mount St. Helens, which had a large eruption on May 18, 1980, and Mount Pinatubo in the Philippines, which exploded in June of 1991 are also in the "Ring of Fire."

How Our Solar System Formed Illustration of a fledgling solar system. Source: NASA/JPL-Caltech By Cynthia Stokes Brown A close look at the planets orbiting our Sun Planets are born from the clouds of gas and dust that orbit new stars. Billions of years ago, circumstances were just right for Earth and the other planets in our Solar System to form. The Solar System that we live in consists of a medium-size star (the Sun) with eight planets orbiting it. The planets are of two different types. The four inner planets, those closest to the Sun, are Mercury, Venus, Earth, and Mars. They are smaller and composed mainly of metals and rocks. The four outer planets — Jupiter, Saturn, Uranus, and Neptune — are larger and composed mostly of gases. What are planets? Where did they come from? Why would some be rocky and some gaseous? What is our planet like? This essay will try to answer these questions. Each of the planets in our Solar System is unique. They vary in size and composition. Source: NASA and the Big History Project The Birth of the Sun Let’s quickly review how our star came into being. Five billion years ago, a giant cloud floated in one of the spiral arms of the Milky Way galaxy. This cloud, called a nebula by astronomers, was made up of dust and gas, mostly hydrogen and helium, with a small percentage of heavier atoms. These heavier atoms had been formed earlier in the history of the Universe when other stars aged and died. This cloud/nebula began to contract, collapsing in on itself. The atoms, once separated, began to jostle each other, generating heat. In the rising heat, the atoms collided more frequently and more violently. Eventually, they reached a temperature at which the protons at the centers of the atoms began to fuse, in a process called nuclear fusion. As they did, a tiny bit of matter transformed into a whole lot of energy, and a star was born. In this way, our Sun came into being. The Birth of the Planets The material in the nebula not absorbed into the Sun swirled around it into a flat disk of dust and gas, held in orbit by the Sun’s gravity. This disk is called an accretion disk. Material in the disk accumulated by further accretion — from sticking together. Each planet began as microscopic grains of dust in the accretion disk. The atoms and molecules began to stick together, or accrete, into larger particles. By gentle collisions, some grains built up into balls and then into objects a mile in diameter, called planetesimals. These objects were big enough to attract others by gravity rather than by chance. If the collisions of planetesimals occurred at high speeds, they could shatter the objects. But when impacts were gentle enough, the objects combined and grew. For some 10 to 100 million years these protoplanets orbited the Sun, some in egg-shaped circuits that resulted in more frequent collisions. This illustration shows the accretion disk of a star that, like our Sun, could go on to form planets from the dust and gas around it. Source: ESO/L. Calçada Worlds collided, combined, and evolved for a dramatic period of time. When it was over, there remained eight stable planets that had swept their orbits clean. A planet is defined as a body that orbits the Sun, is massive enough for its own gravity to make it spherical, and has cleaned its neighborhood of smaller objects. In 2007, researchers at the University of California–Davis determined that our Solar System was fully formed at 4.568 billion years ago. They did this by determining the age of stony materials from the asteroid belt. The Sun sent out energy and particles in a steady stream, called stellar winds. These winds proved so strong that they blew off mostthe gases of the four planets closest to the Sun, leaving them smaller, with only their rocks and metals intact. That’s why they are called rocky, or terrestrial, planets. The four outer planets were so far from the Sun that its winds could not blow away their ice and gases. They remained gaseous, with only a small rocky core. They were made of more gas (namely hydrogen and helium) than the others to begin with, the Sun’s gravity having pulled closer the heavier materials in the original solar disk. Between the inner and outer planets lies an area filled with millions of asteroids — small rocky, icy, and metallic bodies left over from the formation of the Solar System. No planet formed in this area. Astronomers theorize that Jupiter’s gravity influenced this region so much that no large planet could take shape. Jupiter is 11 times the size (in diameter) of Earth and more than twice as big as all the other planets combined. It is almost large enough to have become a star. Of the four rocky planets, Mercury is the smallest, about two-fifths the size of Earth. Earth and Venus are almost the same size, while Mars is about half their size. Astronomers speculate that a smaller object must have hit Mercury, vaporizing its crust and leaving only the larger-than-usual iron core. Conditions on Earth When the rocky planets first formed, they were largely melted (molten) rock. Over hundreds of millions of years, they slowly cooled. Eventually Mercury and Mars, because they are small, solidified and became rigid all the way to their centers. Only on Earth, and possibly on Venus, have conditions remained in an in- between state. Earth has stayed partially molten. Its crust is solid rock, and its mantle is rigid in short-term time. But over geologic time the mantle flows slowly. And the center of Earth consists of a solid iron core rotating in hot liquid called magma. Some scientists and Big Historians use the term “Goldilocks Conditions” to describe conditions on Earth. This comes from an Anglo-Saxon children’s story, “Goldilocks and the Three Bears.” In the story, a young girl named Goldilocks wanders into the home of three bears, who are away. She tries out their porridge, their chairs, and their beds, finding some too hot or too cold, too hard or too soft, too large or too small, but one of each just right. Likewise, Earth is not too hot or too cold, not too big or too little, not too near the Sun or too far away, but just right for life to flourish. Earth’s Moon The rocky object nearest to us is the Moon. Where did it come from? Good question. The Moon orbits Earth, not the Sun, so it is not a planet. The Moon is about one-fourth the size of Earth. The origin of the Moon remains mysterious, but since astronauts walked on the Moon in 1969 and brought back rock and soil samples, we know more about it now than before. The standard argument today holds that a small contending planet, about one-tenth the size of Earth, must have collided with Earth about 4.45 billion years ago. Earth was still red-hot beneath a possible thin new crust. Some of the material from the impact was absorbed into the liquefied Earth but some material ricocheted into space, where it settled into orbit and condensed as the Moon. At first the Moon orbited much closer to Earth. It is still moving away at a rate of almost two inches (four centimeters) per year. The Moon significantly affects conditions on Earth. The impact that produced the Moon tilted Earth on its axis. This causes Earth’s seasonal variations in temperature, since the side tilted toward the Sun for one-half the year’s journey around the Sun receives more direct sunlight. Also, the Moon’s gravity causes the oceans’ tides, reduces the Earth’s wobble (which helps stabilize climate), and slows the spin of the Earth. The Earth used to complete a rotation on its axis in 12 hours, but now it takes 24. Pluto and Beyond Before 2006, students learned that our Solar System had nine planets, not eight. The one counted as the ninth, Pluto, orbits furthest from our Sun. However, in 2006, the International Astronomical Union declared that Pluto does not count as a planet. It is smaller than Earth’s Moon. It orbits way out in a belt of asteroids beyond Neptune (though Pluto periodically comes closer to the Sun than Neptune), and does not have enough gravity to clear the neighborhood around its path. Therefore, it was downgraded to a “dwarf planet,” or a planetesimal. Dust-and-gas clouds surround nascent stars in the Orion Nebula. Proplyds in the Orion Nebula. Source: NASA/ESA and L. Ricci (ESO) Astronomers feel confident that our Solar System formed by accretion because now they are able to glimpse a similar process occurring in part of the Orion Nebula. This planet-forming area is on the near side of a giant cloud complex that embraces much of the constellation Orion, 1,500 light- years from Earth. Since 1993, astronomers have discovered several hundred stars there in the process of formation, most of them surrounded by rings of dust in accretion disks, just like the one they believe produced the solar planets. These clouds of dust and gas around new stars in the Orion Nebula may develop into planetary systems similar to our own. In 1995, astronomers in Switzerland found, for the first time, a planet beyond our Solar System orbiting an ordinary star. Such a planet is called an extrasolar planet, or an exoplanet. As of June 2012, more than 700 exoplanets had been discovered and confirmed. Most of them are giants, closer in size to Jupiter, as larger planets have proved easier to detect hundreds of light-years away. Most are detected not by direct imaging, but indirectly by measuring the effect of their gravity on their parent star or by observing how the light of the parent star dims as the planet passes in front of it. In 2009, the National Aeronautics and Space Administration (NASA) sent a telescope into orbit around the Sun to hunt for habitable exoplanets in the region near the constellations Cygnus and Lyra. This telescope (actually a photometer), the centerpiece of what’s known as the Kepler mission, will monitor 100,000 stars a few hundred to a few thousand light-years away. (One light-year equals 6 trillion miles.) The mission will last three and a half to six years; in the first two years, it has found 17 planets with conditions thought to allow for the development of life. In summary, planets are bodies orbiting a star. Planets form from particles in a disk of gas and dust, colliding and sticking together as they orbit the star. The planets nearest to the star tend to be rockier because the star’s wind blows away their gases and because they are made of heavier materials attracted by the star’s gravity. In the Sun’s system, Earth is one of four rocky planets, but a unique one, with rigid and molten layers. For Further Discussion Think about the following questions: What were the factors working against life forming on the early Earth?Should we be surprised that life formed here at all? What were the factors working against life forming on the early Earth? Should we be surprised that life formed here at all? Share your ideas in the Questions Area below. [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. Reading 1: Skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Reading 2: Understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: What were some challenges that Marie Tharp faced in her work as a geophysicist?How did Tharp's mapping of a Mid-Atlantic Ridge and rift valley help prove the theory of continental drift?Why was Tharp's discovery important to collective learning?Look at the way the panels of the biography progress, moving clockwise from top-left. How does the artist use design to depict Marie Tharp's career as a geophysicist? What were some challenges that Marie Tharp faced in her work as a geophysicist? How did Tharp's mapping of a Mid-Atlantic Ridge and rift valley help prove the theory of continental drift? Why was Tharp's discovery important to collective learning? Look at the way the panels of the biography progress, moving clockwise from top-left. How does the artist use design to depict Marie Tharp's career as a geophysicist? Reading 3: Evaluating and Corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: What does Marie Tharp's story tell you about how theories become generally accepted? What did it take for her ideas to be accepted as scientific fact? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. A "Girl Talk" Geological Revolution: Marie Tharp - Graphic Biography Writer: Bridgette Byrd O'Connor Artist: Thomas Muzzell Marie Tharp spent much of her career in the shadows of male scientists. Yet, her work helped proved the theory of continental drift and our understanding of plate tectonics. Download the Graphic Biography PDF here or click on the image above.

All of the following terms appear in this unit. The terms are arranged here in alphabetical order. accretion — The process by which an object collects matter. For example, planet formation takes place as material orbiting a star gathers together through gravitational or electrostatic attraction, forming larger and larger bodies over time. Archaean eon — The second eon in Earth’s history, a time from 3.8 to 2.5 billion years ago, during which the first living organisms appeared. asteroid — Small rocky, icy, and metallic celestial bodies left over from the formation of the Solar System which can range from a few meters to several hundred kilometers in width. atmosphere — The mixture of gases surrounding a planet. The composition of the Earth’s atmosphere has played a critical role in the development of life on Earth. circadian rhythm — The “master clock” that controls the body’s coordinated timing system, telling it when to work, eat, and sleep. Based on the Sun’s 24-hour cycle, circadian rhythms speed up the body’s metabolism before sunrise to provide energy, and prepare it for sleep at night by lowering blood pressure and slowing the activity of the brain. continental drift — The idea that the Earth’s continents move in relation to each other, so that continents currently separated by oceans were joined together in the past. The theory of plate tectonics explains why continental drift occurs. convergent plate boundaries — Found where two plates move toward each other and collide. Depending on what types of plates are colliding, one may dive beneath the other to be recycled back into the mantle while the other rises up, or both may rise to form a new system of mountains. core (of the Earth) — The dense center of the Earth, made mostly of iron, and some nickel. The movement of molten iron and nickel in the outer core generates the Earth’s magnetic field. crust (of the Earth) — The solid outer layer of the Earth, consisting of moving plates both of the continental (lighter, made of granite) and oceanic (heavier, made of basalts) varieties. differentiation (chemical) — A process early in the Earth’s history that produced different layers within the Earth’s interior, with denser metals sinking to form the Earth’s core, while progressively lighter materials formed the upper layers. divergent plate boundaries — Found where two plates move away from each other. When both of the separating plates are oceanic plates, material from the mantle rises up and creates new seafloor. Earth — The third planet from the Sun in our Solar System, home to many complex life forms and modern human society. exoplanet — A planet outside of our Solar System. gas giant — A type of planet that is composed primarily of gases rather than rock or other solid material. Examples from our own Solar System include Jupiter, Saturn, Uranus, and Neptune. geology — The scientific study of the Earth, including its composition and history. greenhouse effect — A process by which certain trace gases in the Earth’s atmosphere trap heat near the Earth’s surface and so keep the Earth’s climate warmer than it would be otherwise. The Earth emits some of the radiation it receives from the Sun back into space, but greenhouse gases trap some of this radiation before it can escape, thus warming up the climate on Earth, as in a greenhouse. Hadean eon — The earliest period in Earth’s history (4.5 to 4.0 billion years ago), the “hellish era,” when the planet’s formation was still ongoing and was unsuited to life. light spectrum — Electromagnetic radiation arranged in the order of its wavelength; a rainbow is a natural spectrum of visible light from the Sun. Human eyes can only perceive light within the range of the visible light spectrum. We cannot perceive infrared (slightly less energetic) or ultra- violet (slightly more energetic) light. mantle (of the Earth) — The layer of the Earth between the core and the crust; it is mostly solid, but over long periods of time can flow like a thick syrup. Convection currents in the mantle drive plate tectonics. orbit — The path of a body’s motion through space, often dictated by the gravitational pull of one or more larger bodies. ozone — A molecule consisting of three oxygen atoms, in contrast to the more common form consisting of just two oxygen atoms. A thin layer of ozone high in the atmosphere shields the Earth’s surface from harmful forms of ultraviolet radiation. Pangaea — The vast supercontinent formed more than 200 million years ago as plate movements joined the major continental plates together. It is probable that such supercontinents have formed periodically throughout Earth’s history. The existence of a single huge landmass probably reduced biodiversity. planet —A spherical ball of rock, gas, or both, that’s in orbit around a star. Unlike a dwarf planet, a planet clears the area around its orbit of smaller objects through accretion. planetesimal — An object, at least a kilometer or so across but much smaller than a planet, that forms through accretion during the early stages of planet formation. Planetesimals may combine with one another to form protoplanets and eventually planets. plate tectonics — The idea that the Earth’s crust (together with the upper mantle) is broken up into separate plates that are in constant motion, explaining continental drift as well as the distribution of earthquakes, volcanoes, mountain ranges, and other rock structures, and many other features of the planet. Plate tectonics has been a central unifying theory in modern Earth sciences (geology) since the 1960s. protoplanetary disk — A rotating disk of gas and dust grains surrounding a newly formed star or protostar. Over time, accretion within the disk tends to produce planets. rocky (or terrestrial) planets — A type of planet that is composed primarily of rock and other solid material. Examples from our own Solar System include Mercury, Venus, Earth, and Mars. seafloor spreading — A process in which new ocean floor is created as molten material from the Earth’s mantle rises and spreads out at the boundary between two plates. Solar System — The Sun and the objects that orbit it; the area in space in which the Sun’s gravitational pull is the dominant force. spectrum (light) — Electromagnetic radiation (light) arranged in the order of its wavelength; a rainbow is a natural spectrum of visible light from the Sun. subduction zones — An area of convergence (collision) between two tectonic plates where the heavier plate sinks downward beneath the lighter one, which rises up. As the lighter plate rises, it forms volcanic mountains (if the rising plate has continental crust) or volcanic islands (if the plates are converging on the seafloor). Sun — The star at the center of our Solar System. tectonic plates — The huge rigid slabs of rock that the Earth’s crust (together with the upper mantle) is broken up into, which are in constant motion. Some plates carry continents, producing continental drift that dramatically changes the relative locations of continents over millions of years. transform plate boundaries — Found where two plates grind past each other without either producing or destroying crust.

Excerpts from Charles Lyell, Principles of Geology "Sir Charles Lyell, 1st Bt" by John & Charles Watkins. Licensed under Public domain via Wikimedia Commons Charles Lyell (1797 — 1875) was a Scottish lawyer and the foremost geologist of his day. He is best known as the author of Principles of Geology. It popularized geologist James Hutton’s concept of “uniformitarianism” — the idea that the Earth was shaped by slow-moving forces still in operation today. Uniformitarian ideas opposed the common belief among many geologists that unique catastrophes or supernatural events, like the biblical flood in the story of Noah, shaped Earth’s surface. The motto of uniformitarianism was “the present is the key to the past.” Lyell’s friend, Charles Darwin, took that idea and extended it to biology. In fact, Lyell’s Principles of Geology was one of the few books that Darwin carried on his famous voyage on the HMS Beagle — a voyage that led him to write The Origin of the Species. What follows is a summarized version of the original text. Geology defined — Compared to History — Its relation to other Physical Sciences  Geology is the science which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature. It inquires into the causes of these changes. And it describes the influence which they have exerted in modifying the surface and external structure of our planet.  By this research into the state of the Earth and its inhabitants at former periods, we acquire a more perfect knowledge of its present condition. Our views concerning the laws governing its animate and inanimate productions become more comprehensive. When we study history, we obtain a more profound insight into human nature. We can draw comparisons between the present and former states of society. We trace the long series of events which have gradually led to the current state of affairs.  By connecting effects with their causes, we are enabled to classify and retain in the memory a multitude of complicated relations — the various peculiarities of national character. More deeply can we understand the different degrees of moral and intellectual refinement, and numerous other circumstances. Without historical associations, these would be uninteresting or imperfectly understood. The present condition of nations is the result of many previous changes. Some are extremely remote, and others recent, some gradual, others sudden and violent. In a similar way, the state of the natural world is the result of a long succession of events. If we seek to enlarge our experience of the present inner workings of nature, we must investigate the effects of her operations in past eras.  On looking back into the history of nations, we often discover with surprise how the outcome of some battle has influenced the fate of millions today. This remote event may be connected to the current geo- graphical boundaries of a great state, the language now spoken by the inhabitants, their peculiar manners, laws, and religious opinions. But far more astonishing and unexpected are the connections brought to light when we dig deeper into the history of nature. The form of a coast, the layout of the interior of a country, the existence and extent of lakes, valleys, and mountains, can often be traced to earthquakes and volcanoes in regions which are now tranquil. These ancient upheavals are the reason why some lands are fertile, and others are sterile. They determine the elevation of land above the sea, the climate, and various peculiarities.  On the other hand, much of the Earth’s surface was formed by slow operations such as the gradual depositing of sediment in a lake or in the ocean, or to a great increase of testacea and corals.  To select another example, we find in certain areas underground deposits of coal, consisting of vegetable matter which drifted into what were formerly seas and lakes. These seas and lakes have since been filled up. The lands the forests once grew upon have disappeared or changed their form, the rivers and currents which floated the vegetable masses can no longer be traced. And the plants belonged to species which have passed away from the surface of our planet ages ago. Yet the wealth and numerical strength of a nation may now be mainly dependent on the distribution of fuel determined by that ancient state of things.  Geology is closely related to almost all the physical sciences, as history is to the moral. A historian should, if possible, be at once profoundly acquainted with ethics, politics, jurisprudence, the military art, theology; in a word, with all branches of knowledge by which any insight into human affairs, or into the moral and intellectual nature of man, can be obtained. Likewise, a geologist should be well versed in chemistry, natural philosophy, mineralogy, zoology, comparative anatomy, botany; in short, in every science relating to organic and inorganic nature.  With these accomplishments, the historian and geologist would rarely fail to draw correct and philosophical conclusions from the various monuments brought to them by former events. They would know what combination of causes similar effects were relatable to. And they would often be abled to infer information concerning many events unrecorded in the archives of former ages.  But since no one individual can be expert in so many subjects, it is necessary that men who have devoted their lives to different departments should unite their efforts. The historian receives assistance from experts on ancient times and from scholars of moral and political science. In the same way, the geologist should avail himself of the aid of many naturalists. He should particularly gain the help of those who have studied the fossil remains of lost species of animals and plants.  To be fair, we can only compare one class of historical monuments to the records studied in geology — those which unintentionally mark past events. The canoes, for example, and stone hatchets found in our peat bogs, inform us about the arts and manners of the earliest inhabitants. Geology defined — Compared to History — Its relation to other Physical Sciences  Geology is the science which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature. It inquires into the causes of these changes. And it describes the influence which they have exerted in modifying the surface and external structure of our planet. By this research into the state of the Earth and its inhabitants at former periods, we acquire a more perfect knowledge of its present condition. Our views concerning the laws governing its animate and inanimate productions become more comprehensive. When we study history, we obtain a more profound insight into human nature. We can draw comparisons between the present and former states of society. We trace the long series of events which have gradually led to the current state of affairs. By connecting effects with their causes, we are enabled to classify and retain in the memory a multitude of complicated relations — the various peculiarities of national character. More deeply can we understand the different degrees of moral and intellectual refinement, and numerous other circumstances. Without historical associations, these would be uninteresting or imperfectly understood. The present condition of nations is the result of many previous changes. Some are extremely remote, and others recent, some gradual, others sudden and violent. In a similar way, the state of the natural world is the result of a long succession of events. If we seek to enlarge our experience of the present inner workings of nature, we must investigate the effects of her operations in past eras. On looking back into the history of nations, we often discover with surprise how the outcome of some battle has influenced the fate of millions today. This remote event may be connected to the current geo- graphical boundaries of a great state, the language now spoken by the inhabitants, their peculiar manners, laws, and religious opinions. But far more astonishing and unexpected are the connections brought to light when we dig deeper into the history of nature. The form of a coast, the layout of the interior of a country, the existence and extent of lakes, valleys, and mountains, can often be traced to earthquakes and volcanoes in regions which are now tranquil. These ancient upheavals are the reason why some lands are fertile, and others are sterile. They determine the elevation of land above the sea, the climate, and various peculiarities. On the other hand, much of the Earth’s surface was formed by slow operations such as the gradual depositing of sediment in a lake or in the ocean, or to a great increase of testacea and corals. To select another example, we find in certain areas underground deposits of coal, consisting of vegetable matter which drifted into what were formerly seas and lakes. These seas and lakes have since been filled up. The lands the forests once grew upon have disappeared or changed their form, the rivers and currents which floated the vegetable masses can no longer be traced. And the plants belonged to species which have passed away from the surface of our planet ages ago. Yet the wealth and numerical strength of a nation may now be mainly dependent on the distribution of fuel determined by that ancient state of things. Geology is closely related to almost all the physical sciences, as history is to the moral. A historian should, if possible, be at once profoundly acquainted with ethics, politics, jurisprudence, the military art, theology; in a word, with all branches of knowledge by which any insight into human affairs, or into the moral and intellectual nature of man, can be obtained. Likewise, a geologist should be well versed in chemistry, natural philosophy, mineralogy, zoology, comparative anatomy, botany; in short, in every science relating to organic and inorganic nature. With these accomplishments, the historian and geologist would rarely fail to draw correct and philosophical conclusions from the various monuments brought to them by former events. They would know what combination of causes similar effects were relatable to. And they would often be abled to infer information concerning many events unrecorded in the archives of former ages. But since no one individual can be expert in so many subjects, it is necessary that men who have devoted their lives to different departments should unite their efforts. The historian receives assistance from experts on ancient times and from scholars of moral and political science. In the same way, the geologist should avail himself of the aid of many naturalists. He should particularly gain the help of those who have studied the fossil remains of lost species of animals and plants. To be fair, we can only compare one class of historical monuments to the records studied in geology — those which unintentionally mark past events. The canoes, for example, and stone hatchets found in our peat bogs, inform us about the arts and manners of the earliest inhabitants. For Further Discussion Do you think that it’s possible today to study any important question from the perspective of just one academic discipline? Or do most interesting questions require you to consider the perspectives of many disciplines? Share your response to these questions in the Questions Area below.

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. Reading 1: Skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Reading 2: Understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: The comic describes Mary as a "computer." What does this mean?Why was Mary hired? How would you describe her career?How has the artist designed the images in this comic to help you know in which order to read the text?Looking at just images, what do you think is the theme of this comic? The comic describes Mary as a "computer." What does this mean? Why was Mary hired? How would you describe her career? How has the artist designed the images in this comic to help you know in which order to read the text? Looking at just images, what do you think is the theme of this comic? Reading 3: Evaluating and Corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: Have you heard about Mary Golda Ross before reading this comic? Why do you think some people, like Mary Golda Ross, often get left out of the big stories about our collective learning? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. The Rocket Scientist: Mary Golda Ross - Graphic Biography Writer: Bennett Sherry Artist: Kay Sohini Mary Golda Ross was the first female Indigenous engineer. Her mathematical brilliance helped launch humanity on voyages to the stars. Download the Graphic Biography PDF here or click on the image above.

The cosmic beauty of the Sun, our Solar System, and exoplanets. A Protoplanetary Disk NASA/JPL-Caltech This illustration of a young solar system shows the swirling disk of gas and dust that may later form planets. The star system depicted, NGC 1333-IRAS 4B, is 1,000 light years away in the constellation Perseus. Its central stellar embryo is still "feeding" off the material collapsing around it and continues to grow. Astronomers cannot tell how large the star will ultimately become or what types of planets will form around it but they’ve identified enough water vapor in the star system to fill Earth’s oceans five times. Leftovers NASA/JPL-Caltech/T.Pyle (SSC) This illustration shows the debris orbiting a star similar to our Sun at about the time Earth started to form.  In the case of our Solar System, planets eventually formed from asteroids similar to those shown here.  Chunks of matter collided and combined in a process called accretion. Our Sun ESA/NASA/SOHO This recent image of our Sun shows a huge cloud of relatively cool, dense plasma suspended in the Sun’s corona. The hottest areas of the sun look almost white, while the darker red areas indicate “cooler” temperatures of about 60,000 Kelvin (59,726 degrees Celsius or 107,540 degrees Fahrenheit). Coronal loops NASA Bursts of super hot plasma can rise from the visible surface of the sun to a height spanning more than 30 times the diameter of the Earth. The explosive activity of the solar corona (the Sun’s outer plasma layer or crown) can generate “solar winds” and can even affect the weather on Earth. The Blue Marble NASA Goddard Space Flight Center This famous image of Earth, called The Blue Marble, shows how our planet looks from space. Scientists are yet to locate an exoplanet with the unique qualities of Earth.  Its oceans, its atmosphere, its diverse land features and its moderate temperature conditions are just a few of the things that make Earth so special. Mountains of the Moon NASA/GFSC/Arizona State University Most mountains on the Earth are formed as plates collide and the Earth’s crust buckles. Not so for the Moon, where mountains are formed as a result of asteroid impacts. This photograph Shows the Cabeus crater, thought to contain large icy deposits of water and methane. Almost a Star NASA/JPL/University of Arizona The “gas giant” Jupiter is the largest planet in our Solar System. Measuring by diameter, it is about 11 times the size of the Earth and its mass is more than 300 times that of Earth. In some ways, Jupiter is more like a star, or a “failed star” than like a planet since its composition is primarily hydrogen and helium. But Jupiter never heated up enough to start burning its hydrogen, as stars do.  If you look closely to the left side of the image, you can see the shadow cast by Europa, one of the largest of Jupiter’s more than 50 moons. The Eye of the Storm NASA/JPL This collage of color shows swirling clouds around Jupiter's Great Red Spot, as photographed by the Voyager 1 spacecraft. The Great Red Spot is actually a persistent hurricane-like storm that has lasted for at least 180 years.  The storm is so large that 2 or 3 Earths would fit within it. The Rings of Saturn Saturn's rings seem poised to slice through its large moon Titan while the smaller moon, Enceladus, looks on.  The gaseous Saturn, the second largest planet in the Solar System, is orbited by countless particles of ice and dust.  This matter, in sizes varying from tiny grains to larger automobile-sized chunks, reflects light, forming Saturn’s trademark rings. The Neighborhood Big History Project Exoplanets are far more common than originally thought. This diagram shows numerous star systems within 65 light years of the Sun where exoplanets have been observed.  Scientists continue to gather more information about these alien worlds. Close Quarters ESA - C. Carreau This artists depiction of the exoplanet HD 189733b shows the intensely hot planet in relation to its star. Scientists discovered this exoplanet, some 63 light-years away in the constellation Vulpecula, when its star’s light dimmed by 3 percent every time the planet moved in front of it. Primordial Soup It’s hard to know what the surface of an exoplanet might look like up close. In this artist's conception of a hypothetical exoplanet during its solar system's early days, a soupy mix of chemicals pools around the base of the jagged rock formations while meteors fill the sky.  Early Earth may have had a similar look.

A Meteorologist, a Geologist, and the Theory of Plate Tectonics Alfred Wegener, courtesy of the Alfred Wegener Institute for Polar and Marine Research By Cynthia Stokes Brown Alfred Wegener produced evidence in 1912 that the continents are in motion, but because he could not explain what forces could move them, geologists rejected his ideas. Almost 50 years later Harry Hess confirmed Wegener’s ideas by using the evidence of seafloor spreading to explain what moved continents. Balloons and Arctic Air Alfred Lothar Wegener was born in Berlin, the son of a Protestant pastor. He received a PhD in astronomy from the University of Berlin in 1904, but his real love was air balloons. He and his brother, Kurt, set the world’s record in April 1906 for the longest time spent aloft in a balloon — 52 hours. Later that year Wegener joined an expedition to Greenland to track polar air circulation, which could be done with the help of air balloons. (As well, he had always dreamed of polar exploration.) In 1908 he began to teach at the University of Marburg, and in 1911 he co-wrote The Thermodynamics of the Atmosphere, a textbook that became popular; his fellow author, Vladimir Köppen, was a famous climatologist. Wegener married Köppen’s daughter, Else, two years later. Continental Drift Wegener was making his mark as a meteorologist, or weatherman. Yet his mind seemed indifferent to the boundaries of academic disciplines. By 1910 he had noticed on a world map that the east coast of South America fits exactly against the west coat of Africa, as if they had once been joined. He looked for further evidence, found it, and, in 1915, published The Origin of Continents and Oceans. In it he claimed that about 300 million years ago the continents formed a single mass that he labeled “Pangaea,” a Greek word meaning “whole earth.” Wegener was not the first to present the idea of continental drift, as he called it, but he was the first to put together extensive evidence from several different scientific approaches. He used fossil evidence, such as that of tropical plants found on the Arctic island of Spitzbergen. He found large-scale geographic features that matched, like the Appalachian Mountains in the United States and the Scottish Highlands, as well as rock strata in South Africa that matched those in Brazil. He argued against the claim that earlier land bridges between the continents had sunk. He also disputed the theory that mountains formed like wrinkles on the skin of a drying apple, claiming instead that mountains formed when the edges of drifting continents crumpled and folded. Alfred Wegener considers weather data at his desk in Greenland, 1930, courtesy of the Alfred Wegener Institute for Polar and Marine Research Geologists reacted to Wegener’s ideas with widespread scorn. They knew that his ideas, if accurate, would shake the foundations of their discipline. Wegener was not even a geologist — who was he to overturn their field? Besides, he couldn’t explain what force could be immense enough to cause the continents to plow through the Earth’s crust like an icebreaker cutting through frozen sheets. At a 1926 international conference in New York, many speakers were sarcastic to the point of insult; Wegener sat smoking his pipe, listening. In 1924 Wegener accepted a professorship of meteorology and geophysics at the University of Graz in Austria. Six years later he led another expedition to Greenland, this time with government backing, where he would set up yearlong weather-monitoring equipment at three stations on the glacier. Drifting ice delayed the expedition and the Arctic weather proved a great hardship. In November 1930 Wegener led several dogsled teams carrying supplies to his colleagues at the isolated inland station, which was under-provisioned. After celebrating his 50th birthday at the remote weather station, Wegener and his companion, Rasmus Villumsen, died on their return trip west to the coast. Seafloor Spreading The idea of continental drift circulated in scientific circles until World War II, when sounding gear produced new evidence of what the seafloor looked like. The gear, developed in the 1930s, bounced sound waves off the seafloor to determine its depth and features. It happened that the command of one attack transport ship, the USS Cape Johnson, was given to Harry Hammond Hess, a geologist from Princeton University. Hess, then in his late thirties, wanted to continue his scientific investigations even while at war. So he left his ship’s sounding gear on all of the time, not just when approaching port or navigating a difficult landing. What Hess discovered was a big surprise. The bottom of the sea was not smooth as expected, but full of canyons, trenches, and volcanic sea mountains. Ocean floor exploration continued, and by the 1950s other researchers had found that a huge rift ran along the top of the Mid-Atlantic Ridge. That enabled Hess to understand his ocean floor profiles in the Pacific. He realized that the Earth’s crust had been moving away on each side of oceanic ridges, down the Atlantic and Pacific oceans, that were long and volcanically active. He published his theory in History of Ocean Basins (1962), and it came to be called “seafloor spreading.” In the early 1960s, dating of ocean-core samples showed that the ocean floor was younger at the Mid-Atlantic Ridge but progressively older in either direction, confirming the reality of seafloor spreading. Further evidence came along by 1963, as geophysicists realized that Earth’s magnetic field had reversed polarity many times, with each reversal lasting less than 200,000 years. Rocks of the same age in the seafloor crust would have taken on the magnetic polarity prevalent at the time that that part of the crust formed. Sure enough, surveys of either side of the Mid-Atlantic Ridge showed a symmetrical pattern of alternating polarity stripes. That clinched the argument for most geologists. Harry Hess, courtesy of Princeton University Archives Unlike Wegener, Harry Hess lived to see his major theory confirmed and accepted. He helped to plan the U.S. space program and died of a heart attack on August 25, 1969, a month after the Apollo 11’s successful mission to bring the first humans to the surface of the Moon. Plate Tectonics By the 1970s geologists had agreed to use the term “plate tectonics” for what has become the core paradigm of their discipline. They used the term “plates” because they had found evidence that not just continents move, but so do whole plates of the Earth’s crust. A plate might include a continent, parts of a continent, and/or undersea portions of the crust. Wegener’s idea of continental drift had been developed and refined. Geologists today understand that the Earth’s surface, or crust, is broken up into 8 to 12 large plates and 20 or so smaller ones. These plates move in different directions and at different speeds and are not directly related to the landmasses on them. For instance, the North American plate is much larger than the North American continent; the plate extends from the western coast of North America to the mid-Atlantic. Iceland is split down the middle, belonging to two different plates. Over the last 500 million years the continents have come together into one large mass, and then split apart again – possibly as many as three times. Scientists can only guess when the first plates formed and how they behaved further back than that. The force that moves the plates is thought to be convection currents in the mantle under the Earth’s crust. The mantle is solid in the short term, but flows very slowly over geologic timescales. Pockets of hot liquid magma ooze up along extensive mountain ridges deep under the water, one running roughly north-south in the mid-Atlantic and another in the mid-Pacific. Along these ridges are found active volcanoes and hydrothermal (hot-water) vents, also known as “black smokers.” Through these vents pours very hot, mineral-rich water that supports astonishing ecosystems, the only ones on Earth whose immediate energy source is not sunlight. It’s possible that these “vent communities” are where the first living organisms on Earth developed. Where the edges of the plates meet, several things may happen. If both plates carry continents, which are lighter than the ocean floor, they may clash head on, causing high mountains to rise. If one plate is heavier, it may go under the other, a process known as “subduction.” The material of the subducted plate returns to the mantle, recycling the Earth’s crust. Or the plates may move sideways, grinding against each other. This grinding produces cracks, or faults, in the plates, as along the California coast; these fractures are called “transform plate boundaries.” In whatever form the plate edges meet, earthquakes take place; on a global map of earthquake zones, the outlines of the plates are clearly visible. Plate tectonics map, United States Geologic Survey (USGS) The European and North American plates are moving apart at the speed a fingernail grows, about two meters (just over six feet) in a human lifetime. Millions of years in the future, parts of California and Mexico will probably drift off to become an island. Most of Africa is pushing northward toward Europe and will eventually squeeze out the Mediterranean Sea and cause high mountains to emerge along the whole southern coast of Europe. The eastern portion of Africa will split off at the Great Rift Valley and float off into the Indian Ocean. In geologic time, the Earth’s plates are always moving. For Further Discussion Some people are surprised that Wegener’s ideas about continental drift were not immediately accepted. Do you think that explanations that can explain most, but not all, of a problem should be taken seriously? Share your thoughts in the Questions Area below! [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. First read: skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Second read: understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: How did doctors at Johns Hopkins originally obtain a sample of Henrietta Lacks’ cells?Why are HeLa cells considered “immortal”?What breakthroughs in research and health care have HeLa cells led to?Why is it significant that HeLa cells were publicly identified as belonging to Henrietta Lacks?Why do you think the artist chose to include both an image of Henrietta’s son, Lawrence, and a DNA strand in the last frame of the biography? Third read: evaluating and corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: Henrietta Lacks died in 1951, yet her HeLa cells continue to grow today. How does this biography of Henrietta Lacks support, extend, or challenge what you thought about what makes you “you”? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. Henrietta Lacks’ Immortal Legacy - Graphic Biography Writer: Molly Sinnott Artist: Kay Sohini Henrietta Lacks (1920-1951) was an African American woman who grew up on the same land her ancestors had lived on as enslaved people. When she was diagnosed with cancer, doctors took a sample of the tumor they found without her consent. These cells are the source of HeLa cells, the first immortal human cell line and one that proved immensely important to research and the treatment of disease. Yet, Henrietta and her family were not aware that her cells were being distributed and did not have a voice in the way they were being used until recently. Download the Graphic Biography PDF here or click on the image above.

All of the following terms appear in this unit. The terms are arranged here in alphabetical order. adaptation — The capacity of living organisms to change from generation to generation, becoming better suited to their environments. adaptive radiation — The rapid evolution of many new species that possess adaptations that allow them to fill previously empty ecological roles, or niches. bacteria — Very simple unicellular, asexual, and prokaryotic organisms. The first forms of life were most likely similar to bacteria. biodiversity — The variety of life forms in a habitat, whether that habitat is a local environment or an entire planet. biology— The scientific study of living things. biosphere — The entire network of life on Earth; the region of Earth in which living organisms can be found. brain — A cluster of special nerve cells focused on coordinating the activities and vital functions of many different cells and cell groups (or organs). Cambrian explosion — A time in the history of life during the Cambrian period (roughly 542 to 488 million years ago) in which many large fossils appeared and animal life developed an astonishing diversity of structural forms. dinosaurs — Terrestrial vertebrates that first appeared roughly 230 million years ago and dominated the Earth from the beginning of the Jurassic period (about 200 million years ago) until the end of the Cretaceous (66 million years ago)—over 130 million years! Dinosaurs were an extremely diverse group of egg-laying reptiles, some as small as pigeons and others up to 28 meters in length. Fossil evidence suggests that dinosaurs gave rise to modern birds. DNA (deoxyribonucleic acid) — The double-stranded molecule, present in all living cells, that contains the genetic information used to form and maintain the cell and passes that information to offspring cells. eukaryotes — Cells more complex than prokaryotes, with distinct membrane- bound organelles (such as mitochondria) and a nucleus that protects the cell’s genetic material. Many single-celled organisms are eukaryotic, as are most multicellular ones. evolution — Change over time. Applied most frequently to the development of living organisms according to the principles of natural selection, as identified by Charles Darwin in the nineteenth century. extinction event — A specific time in the Earth’s history (or future) when very large numbers of species die off. These events may occur abruptly or over a longer period of time. In the last 600 million years, there have been five events in which over half of all animal species died. fossil fuel — A carbon- based material such as coal, oil, or natural gas that can be used as an energy source. Fossil fuels were originally formed when the remains of living organisms were buried and broken down by intense heat and pressure over millions of years. fossils — The preserved remains of organisms from the distant past. Fossils are usually mineralized or hardened remains of the organisms themselves, but can also include traces of an organism’s behavior (for example, footprints) that have been preserved. gene — A segment of DNA which codes for the production of a specific protein. Genes dictate a particular sequence of amino acids, which when assembled, make up the protein. homeostasis — The capacity of living organisms or cells to regulate internal conditions (for example, temperature) in order to maintain a stable state. iridium — A dense chemical element with atomic number 77 that is more abundant in meteorites than on Earth; its presence at the K-T boundary offered an important clue to what caused the extinction of the dinosaurs. K-T boundary — A layer of clay in the Earth’s geologic rock record between the Cretaceous period and  the Tertiary period. Unusually high levels of the element iridium at the K-T boundary provided scientists with an important clue to how the dinosaurs became extinct. (The K-T boundary is now often called the K-Pg boundary due to a change in how geologists name time periods.) last universal common ancestor (LUCA) — The most recent organism from which all organisms now living on Earth descended; thought to date to about 3.8 billion years ago. life — Four commonly accepted attributes of life are that it uses energy from the environment by eating or breathing or photosynthesizing (metabolism); it makes copies of itself (reproduction); over many generations it can change characteristics to adapt to its changing environment (adaptation); and it can regulate internal conditions in order to maintain a stable state (homeostasis). mammals — Warm-blooded, hairy vertebrates that grow their young inside the bodies of females, and feed their young with milk from mammary glands. marsupials — A group of mammals whose young are born in an undeveloped state and then develop and nurse in a maternal pouch. metabolism — The capacity of living organisms to store, consume, and utilize energy through chemical reactions within cells. This can involve everything from creating nutrients (for example, through photosynthesis), to constructing components of cells, to breaking molecules apart to produce energy. multicelled (multicellular) organism — An organism consisting of more than one cell. The possession of more than one cell allows for the specialization of certain cells, which enables these cells to perform specific vital functions. natural selection — The process by which certain inherited traits become more common in a population because they improve an organism’s chances to survive and reproduce, passing along the traits to the next generation, while other traits become less common because they decrease an organism’s chances to survive and reproduce. niche — An organism’s role within its ecosystem; a set of traits or behaviors employed by an organism within its environment to extract food, avoid predation, and reproduce. The description of an organism’s niche may include its habitat, its place in the food chain, and at what time of the day or night it is active. No two species can occupy the same niche in the same environment for a long period of time. organism — An individual living thing. photosynthesis — The conversion of light energy to chemical energy, which is stored in sugars or other organic compounds, and is performed by plants, algae, and a few other organisms. The first evidence of photosynthesis is from about 3.5 billion years ago. Photosynthesis supplies most of the energy necessary for life within the biosphere and is the source of most atmospheric oxygen, which is released as a byproduct of photosynthesis. prokaryotes — Simple, single-celled organisms, including bacteria, which do not have distinct membrane- bound organelles, and in which genetic material is not bound by a nucleus. Life arose on Earth nearly 4 billion years ago; for roughly the first 2 billion of these years, all living things were prokaryotes. proteins — Large biological molecules composed of long chains of amino acids. Proteins perform numerous functions necessary for life, such as speeding up chemical reactions in cells (enzymes), fighting foreign bodies within an organism (antibodies), providing structural support (structural proteins), and transporting matter within and between cells (motor proteins). reproduction — The capacity of living organisms to create copies of themselves, some of which vary slightly, leading to natural selection and evolution. RNA (ribonucleic acid) — Similar to DNA, but a single strand with slightly different chemistry, this molecule helps to carry out the instructions for protein synthesis specified by the DNA molecule. species — The most specific category in biological classification; organisms are considered to be of the same species if they can interbreed in nature and produce viable, fertile offspring.

Video captions in PDF or text format are provided for the following videos. 5.0—What Is Life? Unit 5 Overview: LifeA Big History of EverythingCrash Course Big History: The Origin of Life Unit 5 Overview: Life A Big History of Everything Crash Course Big History: The Origin of Life 5.1—How Did Life Begin and Change? How Did Life Begin and Change?Threshold 5: Life - captions not yet availableMini Thresholds of LifeLife in All Its FormsCrash Course Big History: Why the Evolutionary Epic Matters How Did Life Begin and Change? Threshold 5: Life - captions not yet available Mini Thresholds of Life Life in All Its Forms Crash Course Big History: Why the Evolutionary Epic Matters 5.2—How Do Earth and Life Interact? How Do Earth and Life Interact?How We Proved an Asteroid Wiped Out the Dinosaurs How Do Earth and Life Interact? How We Proved an Asteroid Wiped Out the Dinosaurs **5.3—Ways of Knowing: Life Codes-H2

Life and Purpose: A Biologist Reflects on the Qualities that Define Life Phytoplankton off Vancouver Island, courtesy of Jeff Schmaltz, MODIS Land Rapid Response Team at NASA GSFC By Ursula Goodenough What’s the difference between nonlife and life? To answer this question, we first need to define life. I’ll lay out what are to me the key hallmarks of life, and then offer a response that flows from such an understanding. A key concept is that every organism is a self, a being. To be a “self” is to engage in two fundamental activities: self-generation and self-maintenance. Self-Generation Self-generation entails the making of a self. If you’re a single-celled organism like a yeast, this involves starting out small, growing large, and dividing into two small daughter-yeasts that start the process again. If you’re a multicelled organism like a human, this involves starting out as a single fertilized egg, developing from an embryo to a fetus, and then taking the path from newborn to old age. In all organisms on our planet today, the key players in self-generation are proteins. When a particular protein is made, it folds up into a particular shape, with crevices and bumps — something like a jigsaw-puzzle piece in three dimensions. These shapes allow proteins to do two major activities. The first is to interact with other proteins, with the bumps fitting precisely into the crevices, to form the thousands of different kinds of chemical structures that make up a cell. Most parts of a cell are constructed from proteins, including the filaments that act as cellular skeletons, the channels that let ions in and out of the cells, and the receptors that let the self know what’s going on in the environment. The second activity of proteins is to serve as enzymes, which allow chemical reactions inside the cell to take place with remarkable efficiency and accuracy. Again, shape is the key. The bumps and crevices bring together the participants in a chemical reaction and ensure that they form the proper kinds of chemical bonds with one another. Japanese macaques in Jigokudani Onsen, Nagano, Japan © Radius Images/CORBIS Self-Maintenance Critical to self-generation is obtaining the molecules and the energy that the self needs to run the store. One strategy is to use photosynthesis, turning the Sun’s light energy into food. The second is to ingest molecules that are made as a consequence of photosynthesis — that is, to eat — and then break them down, using the energy released to drive self-generation. Here again, the shapes of enzymes are critical, but instead of controlling the formation of chemical bonds as in self-generation, they deftly supervise the breaking of chemical bonds, coupling this activity with the formation of energy-rich molecules like ATP (adenosine triphosphate) that keep the cell going. Self-maintenance also entails self-protection, avoiding environmental hazards, predators, and disease. Every Organism is Instructed All the proteins we’ve been thinking about are encoded in genes embedded in DNA molecules. Each gene specifies the amino-acid sequence of a particular protein, and that sequence then defines how the protein will fold up into its functional shape. The full set of genes necessary to pull together a self-generating and self-maintaining self is called a “genome.” A yeast genome and a human genome have many genes in common, notably those concerned with the universal project of self-maintenance, and many others that are distinctive. Daughter organisms inherit copies of genomes from parent organisms, allowing that kind of organism to continue and spread. Embedded in the organization of genomes is the capacity to express certain genes, and hence certain proteins, on some occasions and not others. When it’s time to copy DNA into daughter molecules, the genes encoding the DNA-copying enzymes are “switched on.” When the copying process is completed, these genes are “switched off.” When it’s time for you to make red blood cells, genes encoding the hemoglobin protein are switched on in certain bone-marrow cells but remain switched off in most of the cells in your body. Thus a genome isn’t just a collection of genes; it functions continuously to instruct self-generation and self-maintenance. Every Organism Can Evolve Although DNA is copied with remarkable accuracy, mistakes sometimes happen, giving rise to mutant genes that encode variant amino-acid sequences and hence give rise to proteins with variant shapes. Also occurring are “mutations” that change the timing or magnitude of protein production. The mutation may have no effect, at least in the short term, in which case the mutant daughter may self-organize and self-maintain just like the parent. At the other extreme, it may have disastrous consequences on self-organization and self-maintenance, and the daughter will not survive. The most interesting mutations are those that generate instructions for a viable daughter that is somewhat different from its parent. For example, a parent duck may have delicate foot webbing while the webbing of a mutant daughter may be extra-thick. What happens next is totally dependent on environmental context. If the ducks hang out on mudflats, the mutant feet may allow for surer footing, hence better opportunities for feeding and fleeing predators, and the thick-footed trait will likely spread into future generations; if the ducks live in grasslands, the mutant feet may slow things down and the trait will be less likely to spread. What I’ve just described is Darwinian evolution: inherited variations, coupled with natural selection. The ability of living organisms to evolve has generated the spectacular biodiversity that surrounds us, and without it, we humans would never have shown up. Ernst Haeckel’s 1879 illustration of the “tree of life” shows humans as the pinnacle of evolution, a common view among early evolutionists Every Organism Has Purpose So, with this sense of what life is, can we come up with a single characteristic that distinguishes life from nonlife? Is there one towering difference between a mountain and a whale? After all, both are made of molecules. Both engage in chemistry. Both change through time. For me, the most interesting single generalization is that organisms are purposive whereas nonlife is not. Organisms are about something, for something: muscles are for movement; eyes are for seeing. Organisms have goals. The short-term goal is to self-generate and self-maintain in a given environmental context. The long-term goal is to pass genome copies on to offspring, a goal that succeeds only if self-generation and self-maintenance succeed. Mountains are splendid, to be sure, but in the end they aren’t goal directed. They just are. Taking this perspective, one could say that when life showed up on Earth, something completely new showed up: the emergence of purpose. Whether life, and hence purpose, exists anywhere else in the Universe is unknown and may remain a mystery. Meanwhile, we can enjoy and revel in the astonishing purposiveness that surrounds us here on Earth. A sperm whale © Denis Scott/CORBIS The Matterhorn, one of the highest peaks in the Alps © Dirk Beyer For Further Discussion In the article, Goodenough writes about how “the most interesting single generalization is that organisms are purposive whereas nonlife is not.” What do you think she means by this? Share your response in the Questions Area below. Author bio Ursula Goodenough is a professor of biology and a research leader at Washington University in St. Louis, Missouri. She has devoted years of research to the flagellated green soil alga called Chlamydomonas reinhardtii. Goodenough has also written or coauthored numerous books, including The Sacred Depths of Nature (1998). Goodenough recently initiated research work on biogenesis in Chlamydomonas, contributing to an international effort to produce algal biodiesel as an alternative energy source. [Sources and attributions]

A closer look at the complexity of life and some of its important "mini-thresholds." Mini-thresholds The Big History Project One way of looking at the development of life on Earth is to identify "mini-thresholds," times when life seems to have gotten distinctly more complex. The Brothers National Oceanic and Atmospheric Administration (NOAA) Scientists named the side-by-side columns of this hydrothermal vent The Brothers. Deep sea vents, or "black smokers" as they are often called, occur at oceanic ridges where new sea floor emerges from the Earth's mantle. Scientists believe that some of the earliest life on Earth may have formed around these vents when chemical rich material from within the Earth poured into the oceans. Today's "vent communities" include tube worms, a variety of crustaceans and special bacteria that convert chemicals into energy rather than using the Sun's light. A Single-celled Predator © Carolina Biological/Visuals Unlimited/Corbis In this microscopic image of an Amoeba capturing a Paramecium, the single-celled eukaryotic Amoeba demonstrates remarkable purpose by using its pseudopods to engulf its prey. The Amoeba will change its shape to completely surround the Paramecium and will absorb its meal using organelles called vacuoles. Cyanobacteria Norman Kuring/NASA Ocean Color Cyanobacteria are also known as blue-green algae and their name comes from the Greek word kyanós for blue. This phylum of microorganisms often form large "colonies" and their highly visible blooms, like this one in the Pacific Ocean near Fiji, can be seen and photographed from far above the Earth's surface. Cyanobacteria have been a predominant life form on Earth for at least 2.8 billion years and their oxygen-producing photosynthesis increased oxygen levels in the atmosphere, encouraging further biodiversity. Chloroplasts Kristian Peters The chloroplasts that conduct photosynthesis in the green plants that surround us are thought to have evolved from cyanobacteria by endosymbiosis. According to this theory, free-living bacteria were taken inside, or swallowed up, by cyanobacteria, forming new cells with specialized organelles that had the ability to conduct more complex functions. Chloroplasts capture light energy and carbon dioxide and transform them into energy-rich molecules like ATP and NADPH and, eventually, glucose. Making Oxygen One of the other things that happens when photosynthesis occurs is that a lot of carbon dioxide is transformed into oxygen. When green plants first started in with photosynthesis it altered the atmosphere, greatly increasing oxygen levels. Many species, unaccustomed to an oxygen-rich climate and unable to survive, perished in what scientists sometimes call "the Great Oxidation Event" or "the Oxygen Holocaust." Other life forms liked the new air and flourished. The First Named Cell An illustration by Robert Hooke English natural philosopher Robert Hooke was the first to use the word "cell" to describe the basic unit of life. He was examining a thin slice from a dead cork plant under a microscope and the walled compartments reminded him of the cells that monks of his time often lived in. Hooke published his description of cells and the membranes that separated them in a 1665 book called Micrographia, a work thought to be one of the first scientific bestsellers. Early Brains An earthworm has bunches of nerve cells, called ganglia (singular ganglion), that operate similar to brains, processing sensory information and sending instructions to the worm's other organs to control movement and other functions. This photograph shows the dorsal ganglion in a dissected earthworm, thought to be an example of an early stage in the evolution of brains. Brain Cells © MedicalRF.com/Corbis Nervous system cells or nerve cells, shown here, are called neurons. Mammals can have hundreds of billions of neurons in their brains, all of them working together to process information and send signals to other parts of the body by "firing." Inside each neuron are many of the things found in other types of eukaryotic cells, such as mitochondria, a nucleus with DNA and other organelles. Moving to Dry Land National Science Foundation The Tiktaalik roseae is considered a transitional fossil, or missing link, between fish and the first land-based animals of the late Devonian period. This illustration, based on fossils about 375 million years old, shows how the fishes' front fins evolved into the first arm-like legs, similar to those you might see on reptiles like crocodiles and critical to the new animal's movement on land. Mouse to Man? Muséum National d'Histoire Naturelle Some of the earliest mammals were thought to be mouse-like animals that lived at the time of the dinosaurs and prospered when the K-T impact wiped out the dinosaurs. The fossil shown here is that of a Leptictidium auderiense, a now-extinct mammal that lived about 50 million years ago.

Explore the biosphere, zoom in on some unique ecosystems and learn how activity in the Solar System and plate tectonics can affect the climate and life on the planet. The Biosphere Click here for a bigger version. Big History Project The biosphere is the network of all life on Earth. Many organisms are able to flourish in extreme conditions, but most of the life forms that we are most familiar with live in a relatively narrow band of land and sea identified here as a “comfort zone.” The biosphere includes a wide variety of ecosystems that have their own environmental characteristics and their own biodiversity. The Crater of Doom The Big History Project One of the greatest scientific murder mysteries was solved when scientists located the Chicxulub Crater beneath the surface of the water off of Mexico's Yucatan Peninsula. Geologist Walter Alvarez and others had theorized that a large asteroid had struck the Earth about 65 million years ago, wiping out the dinosaurs. Finding the crater – and confirming the impact date by studying evidence of tsunamis caused by the massive impact – clinched the argument. Climate Currents The Earth's position in relationship to the Sun, its orbital path and its own movement on its axis all contribute to the Earth's climate and to the changing seasons. The position of the continents is also important. The large continental icecaps at the poles can stop the flow of warm temperatures and have contributed to numerous ice ages. Glacial Lake A closer look at a particular ecosystem sometimes offers a clear view of geology. In this picture of Lake Fryxell in Antarctica, glacial melt from a short summer freezes over the briny water below. This frozen environment may not be "comfortable" for humans but numerous species call Antarctica their home and many more include it in their yearly migration patterns. Antarctic Photo Library/National Science Foundation Troglobite World Dave Bunnell Extremophiles are living organisms that thrive in extreme conditions. Some subterranean extremophiles are called troglobites, a word used to describe cave-dwelling creatures that spend their entire lives underground. There are fish, salamanders, crayfish and various insects that have adapted well to this type of ecosystem. Life and Limestone NEON ja Over billions of years the shells of sea creatures accumulated on the ocean floor and became chalk and limestone. In this magnified image, the fossilized structures of ancient life are still visible. Large quantities of organic carbon-based material like this were buried by subduction and the intense heat and temperatures transformed the remains of living organisms into materials like coal, petroleum and natural gas – the so-called "fossil fuels." City of Dirt © Frans Lanting/Corbis This termite mound in Chobe National Park in Botswana, Africa is a good example of how some creatures are able to use innovative construction techniques to refine their habitat. Hundreds of thousands of termites can live in a single mound. The mounds are carefully constructed with extremely effective insulation and ventilation systems, helping to regulate temperature and generate comfortable living conditions. Gravity and the Tides Mila Zinkova In this picture of a tide pool, a colorful world thrives in a shifting environment that can change drastically with the ebb and flow of ocean tides. The force of gravity between the Earth and the Moon pulls on the oceans as the Moon revolves around the rotating Earth, controlling the tides and causing significant variations in the water levels along the coasts. Some "communities" like the daily cycles and flourish in rock crevices or reefs that are sometimes buried in deep water and sometimes exposed to the air.

What is the Biosphere? Earth from space © Science Picture Co/Science Faction/CORBIS By Cynthia Stokes Brown The History of a Word Sometimes the history of a word can tell us a lot about what the word means. The study of words even has its own name: etymology. Often, a closer look at a word unfolds into another story, one that may connect to other people and other scientific studies. The word biosphere was first used by English-Austrian geologist Eduard Suess (1831–1914) more than a hundred years ago in a four-volume work entitled Das Antlitz der Erde, or The Face of the Earth (1885–1908). Suess is also credited with being the first person to propose the existence of the supercontinent Gondwanaland and the ancient Tethys Ocean, based upon his work studying fossils in the Alps and his knowledge of the fossils of Glossopteris ferns that were found on several different continents. At the time, no one knew about plate tectonics (German meteorologist Alfred Wegener didn’t put forth his theory on continental drift until 1912, a couple of years before Suess died), and the best explanation Suess could offer for the presence of marine fossils in the mountains was that the waters of the Tethys Ocean had flooded the whole Earth, not that the continents had actually drifted apart and changed. This is a great example of how limited evidence can sometimes lead scientists to settle on incorrect conclusions.  It also demonstrates how the work of one person can build on that of others, collectively leading to new discoveries about the world around us. Suess combined bio, meaning “life,” and sphere, referencing the Earth’s rounded surface, to express the portion of the Earth that supported life. He invented the word because he felt it was important to try to understand life as a whole rather than singling out particular organisms. He wrote in Das Antlitz der Erde: The plant, whose deep roots plunge into the soil to feed, and which at the same time rises into the air to breathe, is a good illustration of organic life in the region of interaction between the upper sphere and the lithosphere, and on the surface of continents it is possible to single out an independent biosphere. ​As our knowledge of life on the planet evolves, we’ve come to use the word biosphere as a way of explaining the entire intertwined network of life on Earth. This concept combines an understanding of geology, knowledge of the distinct layers that make up the Earth and its atmosphere, and an awareness of the biodiversity surrounding us. We can think of the biosphere as the habitat, or home, for all life on our planet, in all its forms, and with all its intricate biological and geological relationships. Biosphere = the network of all life on Earth Click here for a bigger version. Illustration of the biosphere © The Big History Project Worlds Within Worlds The biosphere is incredibly small — just a thin layer around a medium-size planet. But it’s also incredibly large, when you consider all of the different living things and our planet’s vast expanses of water and land. As with most things that seem large and encompassing, it’s possible to break down the biosphere and to use other words to describe specific environments or habitats. Scuba diver looking at coral reef © moodboard/CORBIS These smaller areas are called “ecosystems,” and they are characterized by particular geologic or climatic features that accommodate certain forms of life. Oceans, jungles, and mountain ranges can be ecosystems, but even more specific places can be their own ecosystems. Think of a cave, a river or river valley, a coral reef, a city, or the “vent communities” that surround black smokers on the ocean floor. Altitude, latitude, longitude, climate, soils, and terrain can all contribute to the distinct features of an ecosystem — the Earth’s geologic processes have produced a multitude of diverse environments. The biosphere boasts incredible diversity and, even in extreme environmental conditions, astounding examples of life’s flexibility and determination. Every organism — from baboons to bacteria, desert snakes to deep-sea sponges — has a specialized way to make a living as it vies for resources and energy and reproduces within its own environment. Examining these individual ecosystems, using biology and geology, reveals the many complex relationships between life and the planet we all share. [Sources and attributions]

Where we investigate images about DNA, evolution, and natural selection. The Complexity of Life © Ocean/Corbis In this image, a monarch butterfly in its caterpillar stage eats a milkweed leaf. The leaf processes energy from the sun and grows in a certain size and shape that distinguishes it as milkweed. The caterpillar, Danaidae plexippus, consumes the plant material (milkweed is its favorite), digesting it and turning it into the energy that will eventually fuel its transformation first into a chrysalis and then into a gold and black butterfly. Charles Darwin Charles Darwin © Bettmann/CORBIS Charles Darwin was a naturalist and an author. His observations of diverse life forms and the way in which they adapted to their surrounding environments led him to develop his theory of natural selection. In 1859 Darwin published On the Origin of Species, introducing his theory on evolution and forever changing the science of biology. This illustration was used as the cover for an early edition of the book. Artificial Selection the food passionates/Corbis Artificial selection in the form of animal and plant breeding has been going on for thousands of years and Darwin's knowledge of it helped him to shape his theory of natural selection. Darwin knew that people had bred animals to favor certain traits and had "cultivated" vegetables or grains to make them more suitable as a food source. This picture shows different varieties of carrots, but color certainly isn't the only trait that can be artificially selected for. Animal breeders will often mate certain individuals so their offspring will carry desired traits forward. Modern understanding of DNA and new "genetic engineering"  techniques have produced new possibilities for artificial selection and new questions about life. A Flounder Hides in the Open Flounder Camouflage © Moondigger A living organism's ability to protect itself from its predators is one of the keys to its survival. In this picture, a flounder blends almost perfectly with the seafloor. Traits such as color are inherited from one generation to the next and, over many generations, certain colors or color patterns will be "naturally selected" by the survival rates of the fish that carry those traits. The same process of natural selection occurs with many other traits such as size, structure and specific internal functions. DNA The Big History Project The double helix structure of DNA, deoxyribonucleic acid, was discovered in 1953 in one of the great scientific races of the modern era. DNA is found in all life on Earth and contains the instructions that cells use to manufacture the materials that make up living organisms. The discovery of DNA and its structure was a major step in understanding the complexity of life and has led to new approaches for understanding and classifying life. Genome sequencing is a technique used by modern biologists to distinguish differences between and among various species. The Alphabet of Life DNA consists off four main "bases" connecting two nucleotide strands in a double helix structure. The four bases pair up: adenine(A) with thymine(T) and guanine(G) with cytosine(C) to connect the two strands, forming a spiral ladder. Different sequences of these four bases spell out individualized genetic instructions for different living organisms. Inside cells, the long DNA sequences are folded and packed into chromosomes, dense "manuals" of genetic information. Chromosomes in a Cell 3D4Medical / Photo Researchers, Inc. In human cells, the long sequences of DNA contained in a chromosome are packed inside the nucleus of the cell, protecting this important genetic information. DNA is so tightly wound within a chromosome that the 51 million to 245 million base pairs in one human chromosome are estimated to be up to two meters long if unraveled. This is an incredibly long length when you consider the microscopic size of the cell and the even tinier nucleus housing multiple chromosomes. An Early View of Human Evolution Ernst Haeckel's Evolution of Man (1879) In this 1879 illustration, German naturalist and artist Ernst Haeckel demonstrates a predominant view of his time, that humans somehow represent the pinnacle of evolution. As biologists continue to study life on Earth and to gather more information, the way that the tree of life and human evolution is depicted continues to change. A Timeline of the Tree of Life In this Big History Project depiction of the tree of life, numerous branches of evolution are placed into a time context. An image of the entire tree of life would contain many more branches and would not be as focused on the history of humans.

Darwin, Evolution, and Faith Jellyfish Lake in Palau, Micronesia © Michele Westmorland/CORBIS By John F. Haught Nothing in contemporary science has proved more challenging to religious believers than evolutionary biology. Disputes about the religious and theological implications of Darwin’s ideas have been going on now for more than a century and a half, and they are as heated today as ever. Darwin and God Why has Darwin’s science been such a religiously troubling idea? In those parts of the world influenced by the Bible and the Qur’an, we may point to at least five reasons: (1) Darwinian biology tells a whole new story of creation, one that cannot be literally reconciled with religious creation stories such as those narrated in the book of Genesis; (2) the evolutionary notion of natural selection seems to eliminate the role of God in creating the various species of life; (3) Darwin’s theory of human descent from nonhuman forms of life raises questions about traditional beliefs in human uniqueness, such as the biblical claim that human beings are created “in the image and likeness of God”; (4) the prominent role of chance or accidents in evolution raises questions about whether a creator truly cares for the world; and (5) the competitive “struggle for existence” inherent in evolution seems at odds with a Universe created by God. What did Darwin think about God? After returning (in 1836) from his sea voyage, he spent the next 20 years or so brooding about the theological implications of his discoveries. He had once taken for granted, as almost everyone else did at the time, that all living species came into being by God’s special creation in the beginning. However, reflecting on what he had observed during his sea voyage, Darwin began to wonder how his Christian faith could be true. His doubts continued to grow, probably reinforced by the anguish he experienced at the deaths of his father and 10-year-old daughter, Annie. In his autobiography Darwin writes: “Disbelief crept over me at a very slow rate, but was at last complete. The rate was so slow that I felt no distress, and have never since doubted for a single second that my conclusion was correct.” Still, Darwin never considered himself the outright atheist that some modern writers have made him out to be. He continued to refer occasionally to the work of a “Creator” who fashioned the Universe and its general laws but who then left its living outcomes to a combination of chance and natural selection. In any case, the religious world of his time was ill prepared for his ideas. Even now, some people are still reeling from the shock Darwin seems to have delivered to traditional beliefs. For others, however, an appreciation of his ideas deepens and widens their faith in God. A depiction of the Garden of Eden by Hieronymus Bosch, c. 1500 Three approaches When Darwin’s On the Origin of Species first appeared, most people in Europe and America read the biblical accounts of origins literally. They thought the world was only around 6,000 years old and all living species had been created separately and in a fixed way at the time of the world’s origins. So, can ancient scriptural accounts of the world’s creation by God be reconciled with Darwin’s new story? Here are three responses to the question: 1. Conflict This approach, whose adherents include both religious believers and skeptics, maintains that evolution by natural selection can never be reconciled with belief in God. Conflict comprises two main groups. On one side are “creationists” and proponents of “intelligent design.” Both groups reject evolution as scientifically misguided. Creationists are Christians (and Muslims) who consider their holy books to be the source of true science and who therefore reject Darwinian evolution as simply wrong. Proponents of intelligent design do not necessarily read the scriptural texts literally, but they consider the complexity of life and subcellular mechanisms too staggering to be the result of natural causes alone. They argue that a supernatural agency is responsible for the complex “design” that exists in the domain of life. There are also those who believe strongly in evolution and use it in their arguments against the existence of a creative and providential deity. These people use the conflict position to reject both creationism and intelligent design as wishful thinking incompatible with evolutionary biology. Especially in the United States, the sense of a conflict between evolution and faith continues to dominate public discussions. There are other ways, however, of looking at the issue. 2. Contrast This approach claims that science and faith are responding to completely different kinds of questions, and so there can be no genuine conflict between evolution and theology. The contrast approach argues that people should simply acknowledge that sacred scriptures are not science and that Darwinian science has nothing to do with faith. In the Roman Catholic Church, for example, Pope Leo XIII in 1893 instructed the faithful not to look for scientific information in biblical texts. Galileo had given his fellow Catholics the same advice back in the 17th century. As far as evolution is concerned, therefore, Darwin’s theory of life’s descent and diversity should never be placed in competition with biblical creation narratives. The creation stories in the Bible were not intended to satisfy scientific curiosity but to urge devotees to be grateful for the richness of creation. The Bible’s intention is to answer questions such as “Why is there anything at all rather than nothing?” and “Is there an eternal reason for trusting that life is worthwhile?” For the most part, Roman Catholics and other mainstream Christian church- es have avoided confusing science with faith and theology by recognizing that they answer different questions and serve different needs. Nevertheless, major strands of fundamentalist and evangelical Protestantism still view the Bible as scientifically accurate, and they consider Darwin’s science to be incompatible with biblical “science.” According to the contrast position, however, reading the Bible as a source of scientific information, whether by creationists or religiously skeptical evolutionists, misses the whole point of the ancient religious literature. 3. Convergence This approach sees truth in both science and religion, and since truth cannot contradict truth, scientific and religious truths must be reconcilable. It adds that in the real world science and faith can enrich each other. This means that, after Darwin, people of faith cannot have exactly the same thoughts about God as before. Religious believers and theologians need to readjust their thinking about God after Darwin no less than they did after Copernicus’s demonstration of a Sun-centered Solar System. Challenges such as evolution are essential to keeping faith and theology alive and healthy. Theology was eventually able to adjust to a heliocentric Universe, so it can now adjust to evolution. The theory of evolution and faith in a creative and providential deity are not mutually exclusive and numerous theologians and scientists have found ways to reconcile these beliefs. In their view, there is no necessary danger to religious faith in thinking bold new thoughts about God after Darwin. After all, even the idea of God, whether people are aware of it or not, has evolved over the course of time, and it will continue to do so. If we take the time to think about God in terms of evolution, convergence argues, religious understanding will have everything to gain and nothing to lose. An illustration showing a variety of bird beaks. An illustration of different bird beaks © Visuals Unlimited/CORBIS Reconciling evolution and faith Ever since Darwin, many Christians and other religious people have been enthusiastic about the discovery of evolution. For example, immediately after On the Origin of Species was published, the learned Anglican priest and theologian Charles Kingsley gave thanks to Darwin for demonstrating how ingenious and creative evolution is and how the exciting new picture of life had enlarged his understanding of the Creator. A God who can make a universe that can make itself by way of natural processes, Kingsley proposed, is much more impressive and worthy of worship than one who is always tinkering with the world or keeping it tied to divine puppet strings. Likewise, the Catholic priest and renowned geologist and paleontologist Pierre Teilhard de Chardin (1881–1955) wrote many works arguing that his own faith makes more sense after Darwin than it did before. As one of the first exponents of big history, Teilhard emphasized that evolutionary biology — along with geology, astrophysics, and cosmology — clearly demonstrated that the Universe is still coming into being. The fact that this process involves struggling, chance, failure, and loss — along with grandeur and beauty — is completely consistent with the fact that the Universe remains unfinished. The role of a creator, Teilhard proposed, is not to force the Universe to fit tightly and immediately into a prefabricated mold, but to open it to an ever-widening range of new possibilities as it moves toward a fresh future. God creates this open universe through natural processes rather than magic. As an evolutionist and a devout Christian, Teilhard saw no contradiction in interpreting the whole of cosmic history as the response to an invitation by God. God, he insisted, is not a dictator but the ultimate and everlasting goal of cosmic process. God always makes room for freedom. Moreover, Teilhard suggested that, with evolution, the meaning of human life and moral action includes our each contributing to the great work of ongoing creation. For Further Discussion Are religion and science, which take different approaches to knowledge, destined to always be in conflict? Please post your thoughts in the Questions Area below. Author bio John F. Haught is a Roman Catholic theologian and senior research fellow at the Woodstock Theological Center at Georgetown University, in Washington, D.C. He is the author of numerous books, including Science and Faith: A New Introduction (Mahwah, NJ: Paulist Press, 2012). [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. First read: skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Second read: understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: Why does the comic call Mexía a “late bloomer,” and why is this important?Why was Mexía’s career significant to the study of life?What do the quotes written by Mexía tell you about sexism in the field of botany and how she responded to it?How has the artist designed the page, text, and illustrations to tell you about Mexía? Third read: evaluating and corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: How does this biography support, extend, or challenge what you have learned about the types of people who study the development of life and do fieldwork in the sciences? Had you ever heard the name Ynés Mexía before? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. The Collector: Ynés Mexía (Graphic Biography) Writer: Bennett Sherry Artist: Kay Sohini As the daughter of a Mexican diplomat, Ynés Mexía (1870–1938) moved around often. Her early life was full of struggle and disappointment, so Mexía moved to San Francisco to seek mental health care. She fell in love with the wilderness and joined the environmentalist movement there. At the age of fifty-one, she went back to school to study botany. During her short, thirteen-year career, she ventured into many wild areas across the Americas, collecting a stunning number of plant samples. She was the first to catalog hundreds of new species, many of which were later named after her. Download the Graphic Biography PDF here or click on the image above.

Crick, Watson, and Franklin: The Race to Discover the Structure of DNA Top: Francis Crick in 1962 © Bettmann/CORBIS. Bottom left: James Watson © Bettmann/CORBIS. Bottom right: Rosalind Franklin © Science Source By Cynthia Stokes Brown In 1953, three English biochemists helped unlock the mystery of life by determining the double helix structure of the DNA molecule. Found in all life on Earth, DNA contains the information by which an organism regenerates its cells and passes traits to its offspring. Setting the Stage Despite his success in formulating the theory of natural selection, Charles Darwin did not yet understand how characteristics are passed from parent organisms to their offspring with the slight changes that make evolution possible and identify each individual. By the middle of the 20th century this was still not well understood. The first part of the century had seen major breakthroughs in physics, such as Einstein’s Theory of Relativity and atomic bombs that used the energy of nuclear fission. After World War II scientists turned to understanding the physical basis (atomic and molecular) of biological phenomena. In the 1950s biochemists realized that DNA, short for deoxyribonucleic acid, delivered the instructions for copying a new organism. A yard of DNA is folded and packed into the nucleus of every cell in pairs called “chromosomes,” with one exception: in the reproductive cells, where the pieces of DNA are not paired. DNA has three constituents: 1) a type of sugar called “ribose”; 2) a phosphate (phosphorous surrounded by oxygen) responsible for its acidity; and 3) four kinds of bases — adenine (A), thymine (T), guanine (G), and cytosine (C). Since these four bases seemed too simple to be able to pass on all the information needed to create a new organism, biochemists were baffled about DNA’s structure and how it worked. However, these four bases combine like letters of an alphabet to describe complex variations in genetic traits. The question became how to study the DNA molecule. Biochemists believed that understanding its structure would reveal how the molecule coded the instructions for copying a new organism. They began taking X-ray images of crystals of DNA, believing that its crystallization meant it must have a regular structure. The pattern of the X-rays bouncing off atoms (a phenomenon called “diffraction”) gave information about their location in the molecule. One of the pioneers of this technique, called “X-ray crystallography,” was Linus Pauling, who worked at the California Institute of Technology in Pasadena. In the early 1950s Pauling, a prominent chemist doing molecular research in the States, seemed a likely candidate to unlock the mystery of life, since he had already concluded that the general shape of DNA must be a helix, or spiral. An illustration of the DNA double helix © the Big History Project The Race The victory, however, went to three people working in England, in one of the great scientific races of all time. One, Rosalind Franklin was working at King’s College at the University of London. The other two, James Watson and Francis Crick were friends and lab mates some 50 miles away at the Cavendish Laboratory at Cambridge University, where they worked cooperatively and shared their ideas. Franklin was from a wealthy, influential family in London. She had earned her PhD in 1945 from Cambridge in physical chemistry. Starting at King’s College in 1951 at the age of 31, she was focused on studying DNA. She became extremely skilled in X-ray crystallography, able to produce clear and accurate diffraction images of DNA crystals by using fine-focus X-ray equipment and pure DNA samples. Over in Cambridge, biochemists were supposed to leave the study of DNA to the lab at King’s College. Francis Crick, age 35 in 1951, was working on his PhD in the crystallography of proteins. He had grown up in a small English village and, since he had failed to qualify for Cambridge, took his undergraduate degree in physics from the University of London. Watson, only 23 in 1951, was at Cambridge as a postdoctorate fellow in biology with limited knowledge of chemistry. He had grown up in Chicago, performed on the national radio show “Whiz Kids,” entered the University of Chicago at age 15, and secured his doctorate from the University of Indiana at just 22. He was at the Cambridge lab to learn crystallography. Between 1951 and January 1953 Franklin reasoned through her precise X-ray diffraction images that: 1) DNA takes two forms (shorter-dryer and longer-wetter), 2) the sugar-phosphate backbones must be on the outside, and 3) the molecule looks the same upside down or right side up. In late 1952 she recorded an especially clear X-ray diffraction image that her col- league, Maurice Wilkins, later showed to Watson in January 1953 without telling Franklin or asking her permission. Franklin and Wilkins did not always communicate well, so his actions were perhaps not surprising. Watson knew at once from seeing Franklin’s photograph that DNA had to be a helix with certain dimensions. He was so excited that he returned to his lab to draw up plans for models that the machine shop would construct out of sheet metal and wire. In building their models, Watson and Crick had to find the answers to several questions. How many strands did the helix have? Which direction did the strands run? Were they on the inside or the outside? How were the four chemical bases arranged? While Franklin believed the answers would come with more X-ray images of better quality, Watson and Crick recognized they were racing against Linus Pauling for a solution and thought that making a model would speed up the answers. First, they tried using two strands, putting them in the center of the model with the bases on the outside; however, this did not produce a chemically acceptable structure. Next, they played around with the shapes of the four bases, using paper models and combining them in different ways. Finally, they visualized a structure that solved the puzzle: If two of the bases were bonded in pairs (G with C), they took up the same space as the other pair (A with T). Hence, they could be arranged like steps on a spiral staircase inside of two strands of sugar-phosphates running in opposite directions. These insights occurred to Crick and Watson between February 4 and February 28, when they announced at lunch in their usual pub that they had found the secret of life. Rosalind Franklin working at King’s College in London © Science Source The News Gets Out The April 25, 1953 issue of Nature published Crick and Watson’s 900-word article, “A Structure for Deoxyribose Nucleic Acid.” Wilkins and Franklin, who both accepted Crick and Watson’s solution, wrote accompanying articles. By the 1960s scientists generally embraced the double helix as the structure of DNA, and in 1962 Wilkins, Watson, and Crick received the Nobel Prize in medicine/physiology for their work. Franklin could not share in the prize as it cannot be granted to someone who has passed away. She had died from ovarian cancer at the age of 37 on April 16, 1958, in London. She had a family history of cancer, but her exposure to X-rays may have contributed to her death. And in any case, she may not have had the chance for the award had she been alive. Crick and Watson never told Franklin that they had used her images (She was mentioned only in passing by Crick and Watson in Nature). Nor did Watson explain this in his popular account of their discovery, The Double Helix (1968). ​It wasn’t until much later that Watson finally admitted in public that he and Crick could not have found the double helix in 1953 without Franklin’s experimental work. If she had survived, would she have been acknowledged and shared in the prize? In their 1953 article Watson and Crick did not discuss how DNA copies itself. They simply included this sentence: “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” Five weeks after their first article in Nature, Crick and Watson published another article proposing the idea that, to make a copy, the double helix unzips, or separates, into two strands — each a backbone of sugar-phosphates with the four bases attached in some sequence. Then the cell uses each strand as a template to assemble another DNA strand from free-floating complementary bases: A picks up T, while C picks up G. This would result in two identical DNA molecules, one a copy of the other. Occasional mistakes in copying enable evolution to occur and each organism to be unique. This idea has been confirmed, while the means for carrying it out have proved to be immensely complex. Crick continued his research in England until 1976, when he moved to the Salk Institute for Biological Studies in La Jolla, California, where he died in 2004. Watson returned to the United States, researching at Harvard from 1956 to 1976. He helped establish the Human Genome Project in the early 1990s and served as president of the Cold Spring Harbor Laboratory on Long Island, New York, until his retirement in 2007. James Watson and Francis Crick in 1959 © Bettmann/CORBIS For Further Discussion In the Questions Area below, try to explain how the discovery of DNA and its structure is an example of collective learning. [Sources and attributions]

Explore the images of this gallery and consider the genetic differences and similarities between humans and other species. The Human Branch Zooming in on the Big History timeline. Click here for a bigger version. Downoad PDF. The evolutionary path that led to modern humans goes back millions of years and merges with the path that also produced all of the primates, including chimpanzees – one of our closest relatives. Cousins? © Fiona Rogers/Corbis Similar DNA isn't the only thing we have in common with our chimpanzee relatives. Primatologists like Jane Goodall and Dian Fossey demonstrated that primates share many other characteristics with humans. Chimpanzees have been observed using simple tools and aspects of their behavior and social interaction mirror that of humans. Comparing DNA The Big History Project A modern way of studying and classifying different creatures is by comparing their DNA. All life on Earth shares this important molecule and the similarities and differences between the DNA of all living organisms separates one species from another. Humans and chimpanzees have a very similar genetic code. Homo Erectus © Carolina Biological/Visuals Unlimited/Corbis Homo erectus, sometimes called Homo ergaster, lived between about 1.9 million years ago and 143,000 years ago. The bodies of this species shared the same general proportions as that of humans and study of their teeth has shown that their growth rates were similar to that of the great apes. Homo erectus are thought to be the first human ancestors to have migrated out of Africa and there is evidence that they built campfires and made stone tools. Homo Habilis Homo habilis was one of the earliest species of the genus Homo and had a slightly larger braincase than its ancestors. Thought to be one of the first species to make stone tools, Homo habilis had long arms and a face similar to that of its ape ancestors. Dental Forensics One of the most important ways that archaeologists can learn about human ancestors is by studying their fossils and material remains. Looking closely at ancient teeth can help distinguish one species from another and can also reveal important information about diet and lifestyle. Acheulean Stone Axes © Alfredo Dagli Orti/The Art Archive/Corbis Acheulean stone tools like these were made by Homo erectus and represent a revolution in toolmaking some 1.6 million years ago. Our ancestors made the multi-purpose tools (sometimes referred to as hand-axes) by flaking off part of the surface to get a better edge and used the pear-shaped tools for digging, cutting wood or other plant material and for cutting and skinning game. Out of Africa Our ancestors made repeated migrations out of Africa. The first time is thought to have been about 1.8 million years ago when Homo erectus traveled into Eurasia, eventually going extinct. More recently, the ancestors of modern humans moved from Africa to Eurasia between 50,000 and 60,000 years ago.

Lucy & the Leakeys The skeleton of Lucy © Alain Nogues/Sygma/CORBIS By Cynthia Stokes Brown *Until the 1950s, European scientists believed that Homo sapiens evolved in Europe, or possibly in Asia, about 60,000 years ago. Since then, excavation of fossil bones in East Africa, pioneered by Mary and Louis Leakey, has revealed that Homo sapiens may have emerged in Africa much earlier.* Human origins Most scientists agree that the human species emerged somewhere in Africa about 200,000 years ago. This understanding is based on fossilized bones and skulls that have been uncovered in East Africa and dated accurately by radiometric dating. These bones and skulls range from 25,000 to 4.4 million years old and show many different stages of human and primate evolution. These fossils have been uncovered by paleoarchaeologists — scientists who study the material remains of the entire human evolutionary line. Based on the fossil evidence, paleoarchaeologists currently tell the following story: For 99.9 percent of our history, from the time of the first living cell, the human ancestral line was the same as that of chimpanzees. Then, about 5–7 million years ago, a new line split off from the chimpanzee line, and a new group appeared in open savanna rather than in rainforest jungle. The old group in the rainforest continued to evolve, and two of its species remain in existence: the common chimpanzee and the bonobo. The new group in the savanna evolved over the millennia into several species (how many is not entirely clear, but at least 18 different ones), until only one was left: Homo sapiens. All the species before us back to our common ancestor with chimpanzees are now collectively called “hominines.” (They used to be called “hominids.”) Try visualizing it like this. Imagine your mother holding hands with her mother, who is holding hands with her mother, and keep going back in time for 5 million years. The final clasping hand would belong to an unknown kind of an ape whose descendants evolved into chimpanzees, bonobos, and, ultimately, your mother. If we count each generation as averaging 14 years, there would be about 360,000 hand-holders in the hominine line. (Thanks to Richard Dawkins, a contemporary English biologist, for this metaphor.) Paleoarchaeologists debate what names to put on the bones they find. They have to decide which ones ought to be considered a separate species. No central authority determines this, so paleoarchaeologists discuss it and try to reach a consensus. They more or less agree on three main categories of species before Homo sapiens; these are Australopithecus (2–4 million years ago), Homo habilis (1.8–2.5 million years ago), and Homo erectus (2–.4 million years ago). Clearly, some of these species must have overlapped during hominine evolution. What scientists now know took many years to figure out. The first early human fossil bones were found in Europe — Neanderthals in Germany in 1857 and Cro-Magnon in France in 1868. Java Man was found in Sumatra, Indonesia, in 1894. Most paleoarchaeologists in the 1920s and ’30s felt certain that Homo sapiens must have evolved in Europe, or possibly Asia, since a group of fossils known as Peking Man was found in China in 1923–1927. Africa, widely known then as the “Dark Continent,” was not considered a possibility largely due to racist thinking. Louis Leakey measures an ancient skull found in Tanzania. © Bettmann/CORBIS The Leakeys look to Africa When did anyone start looking in Africa for hominine fossils? One German professor found a Homo sapiens skeleton in 1913 in Tanganyika (now Tanzania), and a professor in South Africa found a child’s skull there in 1924. But archaeologists denied that these bones were significant. The first to make credible finds were an English couple, Louis and Mary Leakey. ​Louis Leakey was born and grew up in Kenya, in a tiny mission village nine miles from Nairobi, now the capital of Kenya but then a small village on the railroad to Lake Victoria, the source of the Nile River. Louis’s parents were missionaries from England. They hired English tutors for their children, but mostly Louis spent his childhood hunting and trapping with the local Kikuyu boys. Louis spoke Kikuyu as a native language and went through initiation rites with his Kikuyu peers. At the age of 13 Louis built his own house, as was Kikuyu custom. He also found some relics that he recognized as ancient hand axes, even though they were made of obsidian rather than flint, like the ones in Europe were. World War I prevented Louis from being sent to boarding school in England; he was 16 before he traveled to London to prepare for entrance to Cambridge University to become an archaeologist. Mary Nicol grew up in England, but her father was an artist who took his family traveling for nine months out of each year, mostly in southern France, where he painted pictures that he sold in London. He loved Stone Age history and showed Mary many archaeological sites in France. She was only 13 when he died, and her mother sent her to strict Catholic schools in London, where Mary rebelled and was temporarily expelled several times. At 17 she took charge of her own education, learning to fly a glider and to draw, and attending lectures in archaeology. Mary and Louis met in London in 1933 when she was 20 and he 30. Louis was married at the time — with one small child and another on the way — but he and Mary nevertheless began an affair, and in 1935 she joined him in Tanzania during one of his expeditions. They married the following year once his divorce was complete, though Louis’s actions cost him his research fellowship at Cambridge University. Louis Leakey © Jonathan Blair/CORBIS Louis chose the Oldowan Gorge, now called Olduvai Gorge, as his main area of research. It lies about 200 miles southwest of Nairobi, in present-day Tanzania. Olduvai Gorge took shape when a river cut through the sediment that had formed over 2 million years at the bottom of a huge ancient lake. About 20,000 years ago an earthquake drained the lake; after that, the river cut a deep gorge through the sediment of the old lake bed. The river sliced mostly through the shoreline of the lake, revealing the remains of people and other animals that had once gathered there. Almost 2 million years of history are exposed in the 25-mile-long main gorge and in a side gorge 15 miles long, a “layer cake of evolution,” as Virginia Morell, a biographer of the Leakeys, calls it. Olduvai Gorge lies in the Great Rift Valley, a massive geological fault in the African plate. The fault line runs from the Red Sea southward through Ethiopia and Tanzania, down to the mouth of the Zambezi River, in Mozambique. Eventually this crack in the plate will deepen so much that the eastern piece of Africa will break off and move away. Mountains and volcanoes frame the edge of the Great Rift Valley. The volcanic eruptions produce ash, which easily buries and fossilizes bones, making this ideal territory for finding fossils. After being buried under layers of soil for millions of years, the fossils are moved upward as the Earth continues to shift. Life in the field Life was an adventure for Louis and Mary at Olduvai and other sites in the Great Rift Valley. They lived in tents or mud huts with dirt floors and kerosene lamps. Often they had no fresh vegetables or fruit, living on fresh fish, canned food, rice and corn meal, and coffee and tea. (They both smoked cigarettes heavily.) Sometimes Louis shot a gazelle for its meat. Prides of lions prowled their camps at night. Keeping the cars and trucks running in the wilderness proved a monumental task. On occasion the only water available came from watering holes where rhinoceroses wallowed; the soup, coffee, and tea would taste of rhino urine. African servants cooked and served their meals and washed their clothes. The Leakeys’ reward came in living outdoors amid some of the most beautiful scenery in the world — gorgeous volcanic mountains with the Serengeti Plain spread out before them, hosting flamingos, rhinos, giraffes, lions, leopards, antelope, and zebra. The couple worked early and late in the day to avoid the hottest sun, in sand that radiated heat. They used a dental pick and an artist’s brush to reveal, ever so slowly, the hidden fossils of long ago, buoyed by the excitement of finding clues to how humans came to be. Louis and Mary found many ancient tools and fossils of extinct animals, but finding human fossils proved more difficult. In 1948 Mary found a primate skull that they thought might be the “missing link” connecting apes and humans, but it turned out not to be. In 1959 Mary discovered a skull that dated at 1.75 million years old, a find that made the Leakeys famous and led to funding from National Geographic. In 1960 Louis found the hand and foot bones of a 12-year-old, whom he named Homo habilis, thus classifying this species of hominine. Until the 1950s fossil hunting was filled with confusion because no one had a way to date the bones except by estimating the age of the rocks in which they were found. Every expedition had to have a geologist to study the layers of rock, but even those scientists were just approximating the age. Things changed that decade with the advent of radiometric dating, which allowed fossil ages to be identified much more accurately. Carbon-14 atoms would not work for dates that go as far back as early hominines; instead, potassium found in the volcanic ash was used in a potassium-argon radiometric-dating technique. Louis Leakey was convinced that humans had evolved from the apes, which he realized were fast losing their territory in Africa. They had never been studied in the wild, only in captivity. Since knowing more about them would provide insights into hominine behavior, Leakey took the initiative to raise funds for people chosen by him to study apes in their own habitat before it was too late. He looked for young women who could do this work. In 1960 he helped a young Jane Goodall begin her study of chimpanzees in the wild; later, Dian Fossey studied gorillas and Biruté Mary Galdikas studied orangutans. Finding Lucy Meanwhile, others had begun searching for fossil bones in Africa. After Louis Leakey died of a heart attack in 1972, Mary Leakey continued working at Olduvai Gorge; however, the next spectacular find occurred in the Ethiopian part of the Great Rift Valley, at Afar. In 1974, Donald Johanson, an archaeologist from Case Western Reserve University in Cleveland, Ohio, found parts of a skeleton there that dated back 3.2 million years — the oldest hominine bones yet discovered. Johanson nicknamed the skeleton “Lucy,” because that night, as he and the others in camp celebrated their discovery, they listened repeatedly to the Beatles’ song “Lucy in the Sky with Diamonds.” Lucy was assumed to be female because the bones were of a small hominine, roughly three-and-a-half feet (106.68 centimeters) tall. Only about 20 percent of a full skeleton was found, and most of the skull was missing. Fragments suggest it was small, while the foot, leg, and pelvis bones showed that Lucy walked upright. This was important evidence that, in the human line, bipedalism came earlier than brain growth, which previously had been supposed to come first. Anthropologist and author Donald Johanson© Bettmann/CORBIS The Leakey legacy Mary and Louis Leakey raised three sons, who lived with them in the field — Jonathan, Richard, and Philip. These sons stayed in Kenya as grown men, and Richard carried on his parents’ work on human origins, making his first major find in 1972. After discovering another significant skull, he went on to build up the National Museum of Kenya and to run the Kenya Wildlife Service, focusing on saving elephants. After Louis’s death in 1972, Mary became a leading scientist in her own right. She initiated a camp at Laetoli, 35 miles from Olduvai, where the soil dated to 3.59–3.77 million years old. There, in 1976, she found an astonishing set of hominine footprints preserved in volcanic ash, more evidence that hominines of that time walked upright. Mary Leakey received honorary degrees from many universities, including Oxford, Yale, and Chicago. She lived at Olduvai long enough to see leopards and rhinos dwindle to near extinction. In 1983 she ended her fieldwork and moved to Nairobi, where she died in 1996 at age 84. Her granddaughter Louise Leakey, daughter of Richard and Meave Leakey, carries on the Leakey tradition, working in the scorching sun to piece together the story of human origins in Africa. Thanks to the pioneering work of Louis and Mary Leakey, there’s overwhelming evidence to back that story. Confirmed by recent genetic testing, it is clear that Homo sapiens originated in Africa — much longer ago than previously thought — after separating from the chimpanzee line 5–7 million years earlier. The Leakeys spent their lives digging in the earth and tirelessly raising funds in the search for human origins. At a time when few others could entertain the thought, Louis demonstrated that our species had its beginnings on the African continent. For Further Discussion Think about the following two questions and respond to them in the Questions Area below. What are some of the reasons scientists prior to the Leakeys believed that humans originated in Europe or Asia?How did their discoveries lead to both scientific and social changes? What are some of the reasons scientists prior to the Leakeys believed that humans originated in Europe or Asia? How did their discoveries lead to both scientific and social changes? [Sources and attributions]

Jane Goodall: Biography of a primatologist Jane Goodall observes a chimpanzee named Frodo © Kennan Ward/CORBIS By Cynthia Stokes Brown In 1960 Jane Goodall pioneered the study of chimpanzees in the wild, showing the world how similar chimpanzee behavior is to that of humans, and helping to demonstrate the close evolutionary relationship of the two species. An early interest in animal life Jane Goodall was born in London, England, in 1934. Her parents were Mortimer Herbert Morris-Goodall, a car-racing businessman, and Margaret Myfanwe Joseph, a novelist who published under the name Vanne Morris-Goodall. When Jane was just over a year old, her father gave her a stuffed toy, a lifelike replica of a chimpanzee, named “Jubilee” after the first chimpanzee infant ever born at the London Zoo. The toy horrified some of her mother’s friends, who thought that it would give Jane nightmares. They could not foresee the favorable influence it would have on her. Goodall’s interest in observing animal life showed up early. When she was 4, she wanted so badly to know how an egg came out of a hen that she hid inside a small henhouse for nearly four hours waiting to see it happen. Meanwhile, the whole household had been searching for her and had even reported her missing to the police. Goodall with a chimpanzee, in the Gombe National Park © Bettmann/CORBIS Goodall’s fascination with Africa was aroused by reading The Story of Doctor Dolittle by Hugh Lofting. Lofting depicts Dolittle as a kindly doctor who travels to Africa and talks to animals. Jane also read all of the Tarzan books. Her mother encouraged her dream of studying animals in Africa — assuring her that she could do it if she worked hard and believed in herself. Goodall’s parents divorced when she was 12, and when she graduated from secondary school in 1952 her family could not afford to send her to college. Instead, she went to secretarial school and then worked as a secretary, including a job at Oxford University typing and filing. In 1956 a school friend invited her to visit the friend’s family farm in the highlands of Kenya. Goodall went back to live at home, worked hard as a waitress, and in five months saved enough money for the round-trip fare on a ship to Mombasa. A meeting with Louis Leakey In 1957 Goodall visited her friend’s family on their farm outside Nairobi and subsequently found a job as a secretary in the city. Her interest in animals led her to contact Louis Leakey, the famous seeker of hominine bones, who was then working in Africa. He promptly hired her as his secretary. Leakey had been looking for someone to study chimpanzees in the wild and, after he got to know Goodall, felt that she would be perfect. Leakey believed that a woman would be more patient than a man in the field and would be less likely to kindle the aggressions of male chimps. She returned to London to study primates in the London Zoo while he raised funds to support her field studies and arranged her equipment. In 1960, when she was 26, Goodall eagerly traveled 600 miles south-west of Nairobi to live at Gombe Stream Chimpanzee Preserve, on Lake Tanganyika. There, about 150 chimpanzees made their home in a 20- to 30-square-mile area. It took her months to accustom the chimps to her presence but, after nearly a year, most of them would allow her to approach closer than a hundred yards. Observing chimpanzee culture Goodall had little professional training in animal studies. She worked unconventionally, doing things like giving the chimpanzees names instead of numbers and perceiving the individual personality of each one. She also found that baiting the animals with bananas helped to attract them close enough for her to observe their social behavior and to photograph them. Portrait of a chimpanzee © Fiona Rogers/CORBIS Within four months Goodall had observed behavior that contradicted a belief strongly held by archaeologists: that only humans used tools. “Man the toolmaker” was the phrase they used. But Goodall saw a chimp break off a twig, strip its bark, and insert it into a termite mound. When the chimp withdrew the twig, it was covered with delicious termites ready to be licked off. Since then, other researchers have observed chimpanzees using more than half a dozen tools for assorted purposes. Chimp societies across Africa vary in their use of tools. Other animals, including some birds and dolphins, are now known to use tools. Chimps were also widely believed to be vegetarians, but Goodall observed them hunting, killing, and eating small colobus monkeys. Goodall made her findings public in her book In the Shadow of Man (1971). Leakey believed that having a PhD would help give credibility to Goodall’s work. He raised the funds to send her to Cambridge University, where she received in 1965 a PhD in ethology (the scientific study of animal behavior) with a dissertation entitled “Behavior of the Free-Ranging Chimpanzee.” Leakey also sent a professional photographer, Hugo Van Lawick, to Gombe to record Goodall’s work there. The two fell in love and married in 1964. Their son, Hugo Eric Louis Van Lawick, was born in 1967. They called him “Grub” and raised him in Gombe with the chimpanzees. In 1972, Goodall and her husband published a children’s book about their son called Grub: The Bush Baby. But their marriage deteriorated. They divorced in 1974, and a year later she married Derek Bryceson, director of Tanzania’s national parks, who proved to be a deeply compatible partner. However, he died of cancer after only five years of marriage. Goodall speaks at the National Press Club, 1985© Bettmann/CORBIS After Goodall recovered from the death of her husband, she wrote her definitive scientific work, The Chimpanzees of Gombe: Patterns of Behavior (1986). In this book she summarized and analyzed all the data gathered by herself and others at Gombe. By this time the data included acts of warfare, murder, brutality, and even cannibalism by her beloved chimpanzees, challenging her belief in their inherent goodness. For the first 10 years she had believed that they were “rather nicer than human beings,” but now she had to acknowledge that in certain circumstances, such as competition for food, sex, or territory, or under emotions of jealousy, fear, or revenge, their behavior proved as dark and troubling as that seen in humans. At the same time chimpanzees often demonstrated mutual sharing, helping, and compassion. Mothers, children, and siblings developed deep ties, often assisting each other throughout their lifetimes. Older siblings adopted younger ones if a mother died, and would even adopt an orphan from another mother if it had no relative to protect it. Some mothers were more attentive and playful than others, and Goodall observed that their chimps grew up less depressed and aggressive than the chimps whose mothers were less attentive. Some primatologists have criticized Goodall’s methods, especially her use of bananas in feeding stations to attract chimps. They claim that the food causes higher levels of aggression and conflict, distorting normal behavior. But other research has shown similar levels of conflict without feeding stations. Messenger of compassion Since finishing The Chimpanzees of Gombe, Goodall has devoted herself to writing, speaking, and fundraising to support the study and protection of chimpanzees and other wild animals. In 1976 Goodall and a friend founded the Jane Goodall Institute to support research and efforts to protect chimpanzees and their habitats. It has many offices worldwide. In 1991 a group of 16 teenagers met Goodall on the back porch of her home in Dar es Salaam, Tanzania, to discuss what they could do to help the environment, animals, and the global human community. Out of that meeting Goodall organized Roots and Shoots, a global youth program that now has thousands of groups in more than 100 countries. Goodall is a devoted vegetarian and in 2005 published Harvest of Hope: A Guide to Mindful Eating, one of more than 20 books she has written. Goodall remains extremely active in wildlife conversation work. The world has recognized Goodall as a scientist and a special emissary of hope and compassion. Her many awards include numerous honorary doctorates and Disney’s Animal Kingdom Eco Hero Award. In 2002 Secretary General Kofi Annan named her a United Nations Messenger of Peace. Timeline of Goodall's life. Click here for a larger version. Download PDF. For Further Discussion Do you trust that the fields of anthropology, archaeology, and primatology are reliable sources of evidence? Why or why not? Share your thoughts on this in the Questions Area below. [Sources and attribution]

It's hard to pinpoint exactly when and how collective learning first began. The following images, most of them created by contemporary artists, help us imagine how our early ancestors lived and shared ideas. Using Tools © NIKOLA SOLIC/Reuters/Corbis The making and using of tools, shown here in a reenactment, was thought for a long time to be a skill that distinguished humans from other species. But Jane Goodall's work studying chimpanzees and subsequent scientific observations have shown that other species are also capable of making and using simple tools. Symbolic Language © Frank Lukasseck/Corbis Many scientists and scholars consider our use of symbolic language as the quality that really separates us humans from all other species. Ancient cave painting, perhaps the beginnings of written language, has shown up around the world and some examples date to more than 30,000 years ago – though the image here shows a much more recent site in Utah called "Newspaper Rock." Controlling Fire © Anthony Bannister/Gallo Images/Corbis The ability to control and use fire is an important skill that helped enable humans to thrive by providing a heat source that was used for cooking and protection from the cold. Scientists do not know for sure when humans were first able to control fire but evidence suggests this occurred between 400,000 and 1 million years ago. Gorilla Hiroshi Sugimoto Gorilla, 1994 Gelatin silver print 15-3/4” x 23-15/16” (38.7 cm x 58.3 cm) © Hiroshi Sugimoto, courtesy The Pace Gallery Photo courtesy the artist and The Pace Gallery The mountain gorilla, shown here in this artist's impression, is a close relative to humans. There are distinct physical differences and similarities between humans and the "great apes" and primatologists like Dian Fossey also compared their social and behavioral characteristics. Homo Ergaster Hiroshi Sugimoto Homo Ergaster, 1994 Gelatin silver print 47” x 58-3/4” (199.4 cm x 149.2 cm) © Hiroshi Sugimoto, courtesy The Pace Gallery Photo courtesy the artist and The Pace Gallery Private Collection In this artist's impression of Homo ergaster (also called Homo erectus), these ancestors of modern humans are shown competing with other species for a valuable food resource. Homo ergaster lived from about 1.9 million years ago until about 143,000 years ago. Neanderthal Hiroshi Sugimoto Neanderthal, 1994 Gelatin silver print 47” x 58-3/4” (199.4 cm x 149.2 cm) © Hiroshi Sugimoto, courtesy The Pace Gallery Photo courtesy the artist and The Pace Gallery Private Collection Homo neanderthalensis are the closest of our extinct human relatives. In this artist's impression, Neanderthals are shown with tools and clothing. They are also known to have used fire and there is some evidence that they made symbolic objects. Neanderthals lived in Eurasia from about 200,000 years ago to about 28,000 years ago. Cro-Magnon Hiroshi Sugimoto Cro-Magnon, 1994 Gelatin silver print 47” x 73” (119.4 cm x 185.4 cm) © Hiroshi Sugimoto, courtesy The Pace Gallery Photo courtesy the artist and The Pace Gallery Private Collection This is an artist's impression of Cro-Magnon Man, a term once used to describe some of the first modern humans who lived in Europe during the Paleolithic Era about 30,000 years ago. Now scientists consider this group to be similar enough anatomically to humans today that they don't even need a separate name designation.

Follow human migration out of the Great Rift Valley, examine archaeological records from early humans, and contemplate how some of our ancestors lived as hunters and gatherers. Out of Africa The Big History Project The first humans originated in Africa's Great Rift Valley, a large lowland area caused by tectonic plate movement that includes parts of present-day Ethiopia, Kenya and Tanzania. Human ancestors traveled in all directions, constantly in search of abundant food resources and new places to inhabit. Scientists believe there were numerous migratory routes out of Africa by human ancestors but the latest migration by Homo sapiens is thought to have occurred in the last 60,000-100,000 years. Shelter from the Elements John Reader / Photo Researchers, Inc. Human beings have proven themselves very capable of adapting to their environments. The ability to make and use tools, our control of fire and our knack for finding shelter from the elements all contribute to our collective knowledge. Sites like Blombos Cave, shown here, have given scientists evidence about how early humans lived and what they were capable of. Blombos Cave Blombos Cave, on the South African coast east of the Cape of Good Hope (the Southern tip of Africa), is an important archaeological site with evidence of human habitation from about 95,000 to about 55,000 years ago. Materials found at the site can tell us a lot about early human life. Shore Dinner Shell fragments found outside of Blombos Cave indicate that the site's inhabitants used shellfish as a significant source of food energy. There is some evidence that human inhabitants of this site also went deep sea fishing for larger prey. Some shells were made into beads that have been dated at 75,000 years old, an indication that these early humans were also interested in adornment, a form of symbolic expression. Old Stone Age Writing? These pieces of ochre (a mineralized form of iron oxide) were found at the Blombos Cave site. Some archaeologists have gone so far as to claim that the geometric markings on the stones are a form of writing, or recording of information, but there is little doubt that these 75,000 year old pieces at least demonstrate an early form of symbolic thought. Hafting © Bettmann/CORBIS Hafting, the construction of tools that combined stone heads or points with wooden handles or shafts, is considered to be an important innovation by early humans. Resin (such as the sticky sap or "pitch" you might find on a pine tree) and/or sinew (cured bands of animal tissue) was used to secure the sharpened stones to their wooden counterparts. Humans are thought to have begun making hafted tools between 100,000 and 200,000 years ago. Big Game © Gianni Dagli Orti/CORBIS Innovations in tool technology proved extremely important for hunting large game, such as the wooly mammoths shown here. Early humans used stone and hafted tools to bring down the game and then to cut the meat and skins for food and clothing. The Bushmen © Anthony Bannister/Gallo Images/Corbis The Bushmen, a foraging people of Southern Africa, continued with the hunting and gathering lifestyle well into the 20th century. Today, diminishing open lands and increasingly limited public access to stocks of wild food sources have caused most Bushmen like the two hunters shown here to take up a sedentary life. Foraging cultures still exist in the most remote parts of the world but they are few, and far between.

Life as a Hunter-Gatherer Two Bushmen hunters rest © Anthony Bannister/Gallo Images/CORBIS By Cynthia Stokes Brown For 95 percent of their time on Earth, humans have sustained themselves by foraging, that is, by hunting and gathering food from their natural environment. The Evolution of Foraging Living as we do with mass-produced food, markets, and restaurants in every town, and giant supermarket complexes that are often just down the road, it takes some imagination to think of finding food every day in the natural environment. Yet that is just what humans (Homo sapiens) have done for most of their time on Earth — from their appearance about 200,000 years ago until about 11,000 years ago when they began to develop agriculture. Before Homo sapiens evolved, our hominine ancestors foraged for millions of years. A Bushman starts a fire© Anthony Bannister/Gallo Images/CORBIS Foraging means relying on food provided by nature through the gathering of plants and small animals, birds, and insects; scavenging animals killed by other predators; and hunting. The word foraging can be used interchangeably with “hunting and gathering.” Humans are not the only creatures who forage; many animals do too. What is different about human foraging? Answers may vary, but the common idea would be that humans, by means of our ability to communicate verbally, accumulated knowledge, passed it on to younger generations, and worked together cooperatively. These skills enabled humans to gradually refine their foraging methods, further distinguishing us from some of our competitors in the animal kingdom. In fact, one could say that foraging made us human. As fruit trees in the rain forest became less abundant in the cooling, drying climate, the hominines who survived had to find other food sources. As they did, many traits evolved: walking on two feet (bipedalism), loss of most hair, smaller intestines, larger brains, and better communication. These are essentially the hallmarks of being human. One of the most significant steps that hominines ever took was to learn to control fire. They probably did this by tending fires started by lightning. No one knows exactly when this occurred, but hominines may have been using fire to cook meat and roots more than a million years ago. The systematic, controlled use of fire may have begun before Homo sapiens or it may be one of the species’ distinguishing features. Cooked food provided more nutrition, required less chewing, and allowed intestines to shorten, all of which contributed to brain development. The social scene of eating together around a fire may have promoted language development, further contributing to awareness and collective learning. These changes in food consumption were an important step in increasing the flow of energy through human systems. Humans gradually developed their skill in hunting. At first hominines probably scavenged meat that had been killed by other animals. They could drag a carcass to a safe place and use their stone tools to butcher the flesh and crack the bones for marrow. As they developed better weapons and learned to hunt together, they were able to take down larger animals and to devise innovative ways for defeating multiple prey. Herding groups of animals over a cliff and retrieving the carcasses later is one example of this. The Economics of Foraging Climate and environment determined what life was like for any specific group of humans, but some generalizations apply to any group of foragers. They must have possessed a detailed knowledge of their environment. They must have had a large territory in which to forage, larger if they lived in harsh environmental conditions that provided fewer food resources and smaller if they had abundance. Most foragers lived by moving frequently and making temporary encampments. They might have repeated seasonal movements based on animal migrations or the ripening of different plant food sources. Foragers usually lived in small groups of 15 to 30, and split up further when food became scarce or when conflicts arose. Populations grew extremely slowly, if at all. Mothers’ milk provided the only sustenance for infants and nursing extended for three to four years, often preventing a new pregnancy. In any case, mothers could not carry more than one infant at a time. In these close-knit groups, foragers usually shared the food they accumulated, especially prizes of fresh meat. Apparently, foraging societies were the most egalitarian in human history. The Bushmen of Southern Africa Until relatively recently, five different groups of people had been living as foragers in the same place for 30,000 years. And it’s a semidesert — the Kalahari Desert of Botswana, Namibia, and South Africa. The groups each have a name, but collectively they are known as San, Bushmen, or the First People. Most call themselves Bushmen when referring to themselves collectively. How did the Bushmen survive as foragers in such harsh environmental conditions for so many years? Their survival has given the human community a valuable example of the skills of foragers in extremely challenging surroundings. The Bushmen moved every day during the rainy season in search of budding edible greens. They constructed simple shelters against the rain at night. During the dry season, however, they built more stable huts of branches and grass around water sources. Finding water was their essential activity. Sometimes they had to dig deep holes wherever the sand was damp and sip up water through hollow grass straws, often storing it in ostrich eggshells, which held about five cups, more than a day’s supply. The tools of the Bushmen were simple. Men used a bow with poison-tipped arrows and spears for hunting deer, antelope, kudu (another species of antelope), and buffalo. For gathering, the women used a blanket, a sling made of hide, a cloak to carry wood and food, smaller carrying bags, and a digging stick about three feet long and about an inch in diameter. Nuts and roots provided the staple foods. Women also collected fruit, berries, bush onions, and ostrich eggs. Insects — grasshoppers, beetles, caterpillars, moths, butterflies, and termites — supplied a portion of the Bushmen’s protein. Hunting contributed about 20 percent of the total diet, while gathering provided 80 percent. The Bushmen spent a large portion of their time in “leisure” activities — conversation, joking, singing, and dancing. Decisions were reached by consensus, with women having relative equality with men. Chiefs were designated, but they had little additional power. Studies of the Bushmen began in the 1950s when they still lived in the traditional way. By the 1990s most had been forced to adopt subsistence farming as African governments had created game preserves out of some of their former hunting territories. Debates About Foraging People who study foragers are archaeologists and anthropologists. Archaeologists examine human societies through material, cultural, and environmental data left behind. Their work encompasses human societies from the development of the first tools up to recent decades. Anthropologists study contemporary societies that still live much like preagricultural ones. Both types of study are challenging and open to varied interpretations. Conclusions about ancient foragers reached from studying modern foragers are especially tentative, since modern foragers cannot escape completely the world around them. Modern foraging communities often use contemporary tools and partially rely on fairly recent agricultural and technological advances. Their lands have also been greatly limited by development and the overall increase in global population. Traditionally, archaeologists and anthropologists have thought that men did the hunting in foraging societies, while women did the gathering. However, recent studies have challenged this view. People studying apes often point out that primate females can provide for themselves and their offspring, without male assistance. Among many current foraging societies, men and women are flexible about who hunts small birds and animals, and, in some cultures, the hunting and gathering roles are exchanged. The current view holds that past foragers had flexible gender roles, depending on individual skills, knowledge, and the local environment. Mammoth Herd during the Ice Age, a painting by Wilhelm Kuhnert © Gianni Dagli Orti/CORBIS Another ongoing debate among experts concerns the standards of physical and mental health among foragers. Traditionally, foragers were viewed as backward “cavemen” with short, miserable lives, barely eking out an existence. In the 1960s, fieldwork done among surviving foragers (the Bushmen in Botswana, the Aboriginals in Australia, and the Yanomami in the Brazilian rain forest) revealed that foragers enjoy good nutrition obtained in a few hours a day, leaving plenty of time for socializing and grooming. By the 1980s this view was challenged, and no agreement has yet been reached. A third debate concerns how much human foragers have affected the environment in which they lived. For a long time it was assumed that humans had little effect on the rest of nature until they developed agriculture. Since the 1960s, scientists have questioned this assumption. They have pointed to two indications that foragers did make a significant impact. For one thing, archaeologists have found evidence that foragers set fire to large areas of land. Presumably they did this to drive animals out for killing and to promote the growth of fresh plants that would attract animals and would provide food for gathering. Australian Aboriginal use of this practice was given the name “firestick farming.” These fires turned scrubland into grassland and suppressed some species, altering the environment. In addition, whenever humans migrated into new parts of the world, a wave of extinctions of other large animals occurred. In North and South America about 75 percent of the animals weighing more than 100 pounds went extinct within a couple of thousand years after humans arrived. These animals included mastodons, camels, horses, and saber-toothed tigers. In Australia, where humans are thought to have arrived about 40–60,000 years ago, similar extinctions occurred roughly 30,000 years ago. The rate of extinction was about 85 percent and included giant kangaroos and marsupial lions. In Eurasia the extinctions occurred more gradually and included mammoths, woolly rhinoceroses, and giant elk. While debate continues, it may be that a combination of changing climate, human hunting, and other changes brought about by humans may have done these large animals in. For Further Discussion How do you think foragers eventually began to settle down and develop new ways to procure food? Share your ideas in the Questions Area below. [Sources and attributions]

Reading 1: Skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Reading 2: Understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: What was an important contribution that Ales Hrdlicka made to the field of anthropology?What did Hrdlicka believe to be the timeline of human history in the Americas? According to his writing, why did he think this?In 1926, archeologists in Folsom, New Mexico discovered evidence that undermined Hrdlicka's timeline. What did they discover, and was was Hrdlicka's response?In the center of the page, a large image of Hrdlicka is shown blocking a group of early humans moving from Asia toward the Americas. How does the artist use these images to contribute to your understanding of Hrdlicka? What was an important contribution that Ales Hrdlicka made to the field of anthropology? What did Hrdlicka believe to be the timeline of human history in the Americas? According to his writing, why did he think this? In 1926, archeologists in Folsom, New Mexico discovered evidence that undermined Hrdlicka's timeline. What did they discover, and was was Hrdlicka's response? In the center of the page, a large image of Hrdlicka is shown blocking a group of early humans moving from Asia toward the Americas. How does the artist use these images to contribute to your understanding of Hrdlicka? Reading 3: Evaluating and Corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: What evidence does Ales Hrdlicka's story provide about the way collective learning is built overtime?How does it support, extend, or challenge what you have already learned about human evolution? What evidence does Ales Hrdlicka's story provide about the way collective learning is built overtime? How does it support, extend, or challenge what you have already learned about human evolution? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. Ales Hrdlicka: Graphic Biography Writer: Bennett Sherry Artist: Thomas Muzzell An illustrated biography of Aleš Hrdlicka, an anthropologist who both promoted a deeper understanding of human history and impeded collective learning. Download the Graphic Biography PDF here or click on the image above.

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. Reading 1: Skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Reading 2: Understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: In the early 20th century, what was the prevailing belief among archeologists regarding human history in the Americas? How was that different from beliefs held by Indigenous Americans?Why was McJunkin's discovery at the Folsom site significant?The professional archeologists who first came to the Folsom stie years after McJunkin's death never gave him credit for his role in the discovery. How then, decades later, did his contribution begin to be acknowledged?Throughout the graphic biography, McJunkin's face is covered in shadow. Why do you think the artist chose to represent his image in that way?There are two quotes from George Agogini in this biography. Do the two quotes agree with each other? Why do you think these two quotes are significant? In the early 20th century, what was the prevailing belief among archeologists regarding human history in the Americas? How was that different from beliefs held by Indigenous Americans? Why was McJunkin's discovery at the Folsom site significant? The professional archeologists who first came to the Folsom stie years after McJunkin's death never gave him credit for his role in the discovery. How then, decades later, did his contribution begin to be acknowledged? Throughout the graphic biography, McJunkin's face is covered in shadow. Why do you think the artist chose to represent his image in that way? There are two quotes from George Agogini in this biography. Do the two quotes agree with each other? Why do you think these two quotes are significant? Reading 3: Evaluating and Corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: How does this biography of George McJunkin support, extend, or challenge what you have learned about collective learning and the way stories and knowledge are passed through generations? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. George McJunkin: Graphic Biography Writer: Bennett Sherry Artist: Thomas Muzzell George McJunkin was born into slavery, but he became a cowboy and a self-taught naturalist who made a revolutionary archeological discovery. Download the Graphic Biography PDF here or click on the image above.

Using Language to Share and Build Knowledge Cave paintings of cattle at Tassili N’Ajjer, Algeria© Kazuyoshi Nomachi/Corbis By David Christian In the first essay of a four-part series, David Christian explains what collective learning is and why it makes us humans so unusual. What Is Collective Learning? Look at the technology around you: your phone, your computer, your car. Think about how complicated it was to create these technologies. Now ask yourself: If, during your lifetime, you could never speak to another human being, how much of that technology could you dream up? How much of it could you actually build? No matter how smart and creative you might be, the answer is probably simple: “Not much!” Network diagrams,The Big History Project and Chris Harrison/Carnegie Mellon University The same is true of other aspects of human societies: religions, legal systems, literatures, and sciences. Each of us is pretty smart, but all that makes up human culture is not the product of individual geniuses. Instead, all the many different things that express the astonishing creativity of our species were slowly built up over time as millions of individuals shared and combined their ideas and experiences over many generations. The Power of Information A species with lots of information about its environment can exploit its surroundings more effectively. To feed herself and her cubs, a lioness needs to know where to hunt prey. If she doesn’t have this information, she and her cubs will die! But if she can learn about the movements of, say, antelopes, she will have a steady diet and will prosper, probably having more offspring. But the lioness is still like a stand-alone computer — she has only as much memory as she can accumulate in her lifetime. Humans are more like networked computers, with a (more or less) infinite capacity for memory to expand. Because of how we can communicate and share knowledge, we can tap into a vast information network assembled by millions of humans, living and dead. No one person knows it all. Human knowledge is distributed among individuals, shared when necessary, and passed on and added to by each generation. For example, in early foraging societies, elders passed on what they knew to younger individuals. They taught how to hunt, what seasons were best for particular foods, and what social rules would allow one to travel through a neighbor’s territory. As a result, each human gained access to knowledge that had been generated by previous generations, and each individual could add to that body of knowledge. Our species has a colossal amount of information about the world and, therefore, a lot of power. As the 18th-century writer Adam Ferguson put it, “In the human kind, the species has a progress as well as the individual; they build in every subsequent age on foundations formerly laid.” Collective learning empowers humans in another way, too, because individuals who share information can work together efficiently. In fact, we humans now share information so efficiently that we can collaborate in teams of people stretching across the entire globe. No other creature is capable of teamwork on this scale. Sharing information doesn’t give us power just over our surroundings. It also gives us power over other humans. Powerful individuals or groups are usually those with the most information. Well-connected individuals also have larger networks and can form larger and more powerful alliances. Information really is power! Language and Human History If the sharing of ideas is so important, why don’t chimps exchange ideas the way humans do? It’s probably not because they aren’t smart enough. The problem is in the sharing. Chimp language does not allow chimps to share enough information with each other. To get an idea of those limitations, and of how powerful human language is, try telling a friend how to play football without talking, writing, or drawing. With gestures you can really only exchange ideas about what is right in front of you. To share more complex ideas you need a form of language that can create detailed maps of reality. You need to be able to talk about the future and the past, about distant landscapes and ones that don’t yet exist. Think of the power of a simple phrase such as “pink elephant”; by saying those two words I can plant in your mind a picture of something that does not exist and never will. Chimp language cannot do such things, but humans routinely exchange word pictures like that every day. This ability for “symbolic language” has allowed us to cross a major threshold in our ability to communicate: that of collective learning. Human language explains why we can share ideas in such rich detail and across generations. Over perhaps 200,000 years, humans have built and stored a vast body of technologies, rituals, stories, and traditions that provide more and more powerful ways of dealing with our surroundings and with each other. That’s why I believe collective learning is the key to understanding human history! When Did Collective Learning Begin? That’s really a way of asking, “When did human history begin?” To tackle this difficult and important question, we need to approach the problem like an archaeologist. If you were an archaeologist, what would you expect a species capable of collective learning to leave behind? What evidence might you find? One possible answer: technologies such as stone tools! That’s exactly why Louis Leakey thought that we should regard Homo habilis as humans. As early as 2 million years ago, they were making simple stone tools. But there’s a problem. Thanks to the work of Leakey’s protégé Jane Goodall and other primatologists, we now know that chimps can make tools; for example, they use twigs to get tasty termites out of termite mounds. In fact, lots of animals use tools, but none seem to accumulate new technologies over time as well as humans do. On the other hand, by about 50,000 years ago, we know that some humans had migrated to Australia. To do so they must have crossed approximately 40 miles of open water, thus possessing great boat-building and navigational skills. At the same time, in Eurasia, new types of tools and new kinds of art and sculpture started to emerge. But collective learning likely predates 50,000 years ago. At sites in Africa, there is tantalizing evidence for innovative thinking and new technologies from 100,000 years ago or even earlier. Delicately made stone tools may have appeared 200,000 years ago. At sites like Blombos Cave in South Africa — where there is evidence of human habitation almost 100,000 years ago — we also find ochre, a rock whose dust can be used to paint the body. If people were painting themselves they may have been thinking in new ways, suggesting a richer form of language. We also find signs that people learned to attach stone blades to sticks. This technique, “hafting,” is unique to humans and illustrates how collective learning works. As the use of small stone blades became widespread, we presume that these early humans knew how to use their sharp stone edges to shape wooden spears or digging sticks. We also know that foragers often used natural resins and fibers to carefully bind shaped blades to shafts, to form spears or arrows. Combine these ideas and you have a new technology: hafting. Hafted tools© Bettmann/CORBIS As complexity theorist Brian Arthur puts it in his Nature of Technology: ...every novel technology is created from existing ones, and...every technology stands upon a pyramid of others that made it possible in a succession that goes back to the earliest phenomena that humans captured. A Model of Collective-Learning Networks Now we need to start thinking about how collective learning works in different periods of human history. The diagram opposite is a very simple map of the relations between three people (or perhaps three groups of people). We will use it to help us think about how humans exchange information and how these exchanges have shaped human history. You can imagine this as a map of information exchanges or collective learning between individuals in a few small communities of foragers. Could you draw a similar map of relations in your classroom? How similar would it be? You might find small clusters of close friends, but you would also find that some individuals have more links than others. And you’ll find that some individuals have links that reach well beyond their own clusters of friends and well beyond the classroom. If you map all the links you’ll find that it’s the long-distance links that hold entire networks together and ensure that information can circulate through the whole network. As the course progresses we’ll look more carefully at the relationship between networks and collective learning, and how this has impacted human history. Simple Networks,The Big History Project For Further Discussion Why and how has collective learning changed over time? Share your ideas in the Questions Area below. [Sources and attributions]

All of the following terms appear in this unit. The terms are arranged here in alphabetical order. anthropology — The scientific study of human beings and human culture, including beliefs, customs, and archaeological records. archaeology — The scientific study of human activity in the past, primarily by finding and examining objects that humans created or interacted with. australopithecines — An early group of hominine species with brains similar in size to those of chimpanzees; they flourished in Africa between 4 and 1 million years ago. bipedalism — The ability to walk on two rear limbs (legs). culture — The customs, values, beliefs, and general patterns of behavior of a particular group of people. foraging — Relying on wild (uncultivated) plants and animals for sustenance; hunting and gathering. Foraging was the dominant way of life during the Paleolithic era. fossils — The preserved remains of organisms from the distant past. Fossils are usually mineralized or hardened remains of the organisms themselves, but can also include traces of an organism’s behavior (for example, footprints) that have been preserved. genealogy — The study of lineage and family history. genetics — The scientific study of how traits are inherited. hominines — All bipedal species in the human line since it diverged from the common ancestor with chimpanzees; first appeared 8 to 5 million years ago. The only survivors of this line are Homo sapiens, or modern humans. Homo ergaster or Homo erectus — A hominine species that originated in Africa around two million years ago and migrated into Eurasia, reaching as far as China and Java. Almost as tall as modern humans, their brains were larger than those of Homo habilis, and they may have been able to control fire. Homo erectus and Homo ergaster may have been the same species. Homo habilis — A hominine relative of human beings that appeared in Africa between 2 and 3 million years ago, and was able to make simple tools. Homo sapiens — The scientific name for our species, which is thought to have evolved in Africa between 200,000 and 300,000 years ago. marsupials — A group of mammals whose young are born in an undeveloped state, and then develop and nurse in a maternal pouch. migration — Movement of animals from one place to another, often in search of more abundant resources. Neanderthal — A species of hominine very closely related to our own species, Homo sapiens, that went extinct roughly 35,000 to 30,000 years ago. Genetic research shows that the DNA of people with Eurasian ancestry is partly (a few percent) Neanderthal. Though Neanderthals have sometimes been portrayed as brutish or stupid, they were probably very similar to Homo sapiens, and some experts even consider them part of our species. nomadic — Describes a way of life in which people move from place to place rather than settling in a single location; movements are often dictated by climate and availability of food sources. Paleolithic era — A long, early era of human history that featured the creation and use of many different types of stone tools; literally means “Old Stone Age.” paleontology — The study of prehistoric life on Earth using the fossil record. primate — A member of the order of mammals appearing between 60 million and 70 million years ago that is characterized by a relatively large brain, hands with multiple movable fingers and nails instead of claws, and eyes positioned on the front of the skull to enable stereoscopic vision. symbiosis — An interdependent relationship between two different species that live in close contact with one another; may be beneficial to both species, or beneficial to one but neutral or harmful to the other. symbolic language — A powerful form of communication; much more powerful than communication by  other animals because it can convey much more information, much more precisely. Symbolic language makes collective learning possible because it allows humans to share huge amounts of accumulated information generation to generation. taxonomy — The science of classifying different forms of life based upon distinguishing characteristics.

All of the following terms appear in this unit. The terms are arranged here in alphabetical order. agrarian civilization — A large, organized human society that relies on a large number of its members producing food through agriculture. May incorporate hundreds of thousands or even millions of people, and include cities together with their surrounding farmed countryside. Common features of agrarian civilizations include coerced tribute (“taxing”), specialized occupations, hierarchies, state religions, kings or queens, armies, systems of writing and numbers, and monumental architecture. agrarian era — An era of human history, beginning roughly 10,000 years ago and lasting until the beginning of the modern era, when the production of food through agriculture was a central focus of many human societies, and a large number of people living in those societies worked the land. agrarian surplus — The production of more crops and other food than immediately needed. One key to how a civilization develops specialized roles and a division of labor. The society that produces food in surplus can afford to have a class of people who don’t need to farm. These people can fulfill other duties in an increasingly complex society, including the roles of leaders, judges, bureaucrats, doctors, priests, artisans, slaves, or soldiers. agriculture — The cultivation of plant and animal species that are useful to humans for food or other purposes. A form of symbiosis, it generally results in genetic changes in the “domesticated” species over time. Agriculture can be vastly more productive than foraging technologies, though agricultural societies are also vulnerable to crop failure, disease, and other problems. Its appearance marks a fundamental transformation in human history. artificial selection — The process by which humans breed plants or animals in order to cultivate certain desirable characteristics. city — A large center of population (usually with tens of thousands of people or more) with its own social and trade structure. civilization — A human society having dense population, large public buildings, a central authority, and, often, a system of writing or other means of recording information. cuneiform — The world’s first known system of writing, written with reeds on wet clay in Mesopotamia (Sumer); the first written records date back a little more than 5,000 years. domestication — The process by which humans breed a population of plants or animals to make them more productive, easier to control, or more beneficial to humans in other ways. Domestication results in genetic changes to the species and often works as a form of symbiosis, in which domesticated species benefit from human protection. Agriculture depends on the process of domestication. Fertile Crescent — An area of fertile river valleys in Mesopotamia that contains the earliest evidence of agriculture. geography — The study of how physical features of the Earth and human interactions with the physical environment vary from place to place; often overlaps with geology, political science, economics, and many other disciplines. government — A person or group of people who maintain leadership and control over a city, state, or civilization. history — The study of past events. ice age — A cold period on Earth when much of the globe is covered by ice sheets and glaciers. irrigation — The control of the flow of water to support agriculture. Mesopotamia — A region between the Tigris and Euphrates rivers that was the site of some of the earliest agrarian civilizations. Much of the region lies in modern-day Iraq. monumental architecture — Large structures, such as pyramids, temples, public spaces, and large statues, that tend to appear wherever powerful leaders emerge; a feature of all agrarian civilizations. Natufians — A group of people who lived in part of the Fertile Crescent some 12,000–15,000 years ago. Though they did not farm, they lived in settled villages, and their culture suggests some of the transitional stages between foraging and early forms of agriculture. pastoralism — A way of life similar to agricultural, but based primarily on the exploitation of domesticated animals rather than plants. To allow their domesticated animals to graze over large areas, pastoralists are generally nomadic. power (relations among people) — Power relations in human societies can usefully be analyzed into two fundamental forms: Power from below (consensual or bottom-up power) is power granted by followers to a leader to ensure the successful achievement of group tasks. Power from above (coercive or top-down power) is power that depends on the ability of rulers to impose their will by force. sedentism — Living in one place for most of the year; rare in foraging societies but became widespread with the adoption of agriculture. Sedentism developed because agriculture made it possible to produce more resources in a given area and encouraged farmers to stay in one place to protect their crops. state — A regionally organized society, capable of imposing its will by force, based on cities and their environments, and containing populations of tens of thousands and up to many millions of people. Sumer — A region in Mesopotamia that was the site of one of the earliest agrarian civilizations. teosinte — A type of wild maize that is the ancestor of corn. Uruk — A major city that emerged in Sumer about 5,500 years ago; one of the first big cities to emerge in the world, and probably the largest city in the world at its height. village — A small, settled community of people.

Explore the images of this gallery and consider how increased productivity from the land, food surpluses, and swelling populations changed the types of communities that humans lived in. The Cradle of Civilization The Big History Project As with agriculture, the first human civilizations emerged in the Fertile Crescent. More than 5,000 years ago, large agrarian communities became full-fledged cities like Uruk, Ur and Nippur in Mesopotamia and, later, in the Nile Valley of Egypt at Nekhen and Memphis. Agriculture in the Indus Valley fed the growth of cities at Mohenjo-daro and Harappa. Civilization would come thousands of years later in the Americas. The Americas Due at least in part to the same environmental reasons of geography and climate that affected the rise of agriculture, civilizations emerged much later in the Americas than in Eurasia. The north-south orientation of the Americas slowed down the exchange of information, with the Andes Mountains in South America acting as a natural barrier between different communities. Eventually people congregated in what is now central Mexico and agrarian civilizations like the Olmecs, the Maya and Aztecs emerged. Further south the Incas built an enormous empire based in and near present-day Cuzco, Peru. The Aztec and Inca empires would flourish until 500 years ago when European explorers defeated these cultures in their prime with steel weapons and disease. Irrigation © George Steinmetz/Corbis The earliest agrarian civilizations emerged in river valleys because the seasonal flooding of rivers enriched the soils by spreading silt and because access to water was extremely important for cultivating crops. With the advent of irrigation, humans learned to divert water supplies – enabling larger harvests and allowing for storage of water for use by the community. An Energy Revolution © Bojan Brecelj/CORBIS After domesticating other animals, farmers learned to use their livestock not only as a source of food and clothing material but as "workers" in the field. It was an "energy revolution." With the benefit of an ox, perhaps bred over several generations to be larger and stronger, farmers were able to till more land, producing larger harvests and eventually generating the kinds of food surpluses that led to other aspects of civilization. Plowing the Fields With some people plowing fields and producing excess food, other people had more time to turn their attention to other endeavors, including art. This Egyptian fresco from about 1300 BCE depicts the daily life of farmers in the Nile River Valley. Cuneiform © Peter Aprahamian/CORBIS One of the earliest known forms of writing, cuneiform, emerged in Sumer in Mesopotamia about 5,000 years ago. Cuneiform (a later, advanced form is shown here) was produced by pressing the rigid, wedge-shaped edge of a cut reed into wet, unhardened clay. Once the clay dried and hardened, the inscriptions proved extremely durable. Hieroglyphics © Ladislav Janicek/Corbis Another form of early writing was Egyptian hieroglyphics, like these from the Medinet Temple of the Dead of Ramses III in Luxor, Egypt. Writing, a major advance in the human use of symbolic language, made an enormous contribution to collective learning. The Code of Hammurabi © Gianni Dagli Orti/CORBIS One of the greatest legacies of Mesopotamian civilization may be the The Code of Hammurabi, one if the earliest written records of law. Hammurabi (a Babylonian king from about 1792-1750 BCE) is shown here receiving "the law" from the Mesopotamian Sun god Shamash in a sculpture called the Stele of Hammurabi. Greek Silver © Hoberman Collection/Corbis With civilizations came writing, laws and increasingly complex systems of exchange. This Greek silver coin called a tetradrachm was minted in Athens at about 150 BCE but metal coins are thought to have been in use at least 500 years before that. Other civilizations used shells, precious stones and other materials as units of money. The Mighty Tenochtitlan by Diego Rivera © Charles & Josette Lenars/CORBIS Although a contemporary painting, this fresco by Diego Rivera illustrates some of the most important characteristics of early civilizations. The Aztec city of Tenochtitlan pictured here included monumental architecture, complex systems of government and trade, and an elite ruling class with supreme power.

Geography Shapes Culture and History in the Far East A marble bust of Buddha from the Tang Dynasty © Christie’s Images/CORBIS By Craig Benjamin, adapted by Newsela The complex and powerful states, dynasties, and civilizations that emerged in East Asia were strongly influenced by the environments in which they prospered. Floods Help Shape a Worldview What were the geologic and geographic advantages favoring certain locations that facilitated the establishment of villages and towns — some of which grew into cities — in various regions of East Asia? What role did climate play in enabling powerful states, and eventually agrarian civilizations, to appear in some areas while other locations remained better suited for foraging? Let’s begin to answer these questions with a story about floods in China. China’s two great rivers — the Yangtze and the Yellow — have been susceptible to regular flooding for as long as we can measure in the historical and geological record; nothing, however, can compare to the catastrophic floods of August 19, 1931. In just one day the Yangtze River rose an astonishing 53 feet above its normal level, unleashing some of the most destructive floodwaters ever seen. These floods were a product of a “perfect storm” of conditions — monsoons, heavy snowmelt, and tremendous and unexpected rains that pounded huge areas of southern China. As all this water poured into the Yangtze’s tributaries, the river rose until it burst its banks for hundreds of miles. The results were devastating — 40 million people impacted, 24 million forced to relocate, and more than 140,000 people drowned. An area the size of Oklahoma was underwater, and the southern capital city of Nanjing was flooded for six weeks. A 12th century painting The Yellow River Breaches Its Course, Beijing Palace Museum Such is the power of nature. People throughout history have been forced to acknowledge it, but in China the realization has led to a widely quoted maxim: “Heaven nourishes and Heaven destroys.” Despite the best efforts of emperors to regulate episodes of environmental boom and bust, these natural and uncontrollable cycles have profoundly influenced the core foundations of Chinese and East Asian culture. The behavior of rivers has become a model for the constant flux of natural forces, the balance between nature as creator and nature as destroyer. This is an example of why historical processes rely so heavily on the environmental context in which they take place. Big historians believe that understanding geography and climate is necessary background to the study of any civilization. In this essay we take look at the physical geography of China, Korea, and Japan to see how it has influenced the cultural and political history of East Asia. China China and the United States share several geographical similarities. They are about the same size, reside in the middle latitudes of the northern hemisphere, and have lengthy coastlines and diverse topographies. China is located in the eastern part of Asia, along the west coast of the Pacific Ocean, a region that is also home to the Korean Peninsula and the island nation of Japan. With a total land area of more than 3 million square miles, China is the third-largest country in the world after Russia and Canada. China also has extensive seas and numerous islands, and a coastline that extends for more than 11,000 miles. In a country the size of China, it is hardly surprising to find a great variety of topography, climate, and vegetation. The eastern regions are fertile alluvial plains that have been built up by China’s great river systems. This is the region that has been densely settled and farmed for thousands of years, and where all the great dynasties and their capitals were located. Along the edges of the Mongolian Plateau in the north lie extensive grasslands, the home of the pastoral nomadic peoples who interacted (and competed and clashed) with China’s sedentary populations virtually from the beginning of history. The vast “grass oceans” hosted Saka and Yuezhi, Xiongnu and Hun, Jurchen and Mongol — militarized archer warriors whom segments of the Great Wall were built to keep out. The southern regions of China consist of hill country and low mountain ranges. The south receives extensive rainfall, which is ideal for rice cultivation. The success of rice farmers through the ages — from around 8000 BCE, when the grain was first harvested and domesticated — explains why China has been consistently able to support a very large population. China is also a mountainous country. The highest of these mountain ranges, including the Himalaya, the Karakoram, and the Tien Shan, are all located in the west, where they have long acted as a formidable barrier to communication. To make these topographical barriers even more challenging, the mountain ranges are interspersed with harsh deserts like the Taklimakan and Gobi. Great Wall of China © Frans Lemmens/Corbis There is little arable land for agriculture in the west, so the smallish populations there have been confined to oasis settlements or have lived as pastoral nomads on the steppes. This led to Chinese civilization emerging in the more arable east, north, and south. Isolated by its own “wild west,” China was cut off from the rest of Eurasia and from competing agrarian civilizations. Even today, these formidable topographical barriers, and the vast distances necessary to cross western China, affect China’s relations with its western neighbors. Yet these barriers have their advantages too. Chinese governments from the earliest dynasties have been forced to focus on internal cultural and ethnic integration rather than on external expansion. Although the mountains and deserts of the west limited contact between early imperial dynasties and other Afro-Eurasian civilizations for thousands of years, they were eventually breached by traders moving along the Silk Roads, the first connection between China and the rest of Afro-Eurasia. It was the Silk Roads (land and maritime) that allowed many of the ideas and technological inventions of East Asian civilization — paper, printing, gunpowder — to reach the West, where their impact was profound. China’s two river systems have also greatly influenced its history and culture. The Huang He in the north, called the Yellow River because of huge amounts of silt (yellow loess soil) that it carries from the plains into the ocean, rises in the mountains of Tibet and flows 2,920 miles to the Yellow Sea. During its journey it crosses the high western plateau, flows through the arid northern deserts, and then spills out onto the broad alluvial plain. About midway along its course the river takes a series of sharp turns — the so-called “great bend” — before resuming its path. This bend was long perceived as a frontier, the very edge of the civilized world beyond which lay the endless and dangerous steppes where one entered the realm of the “barbarians” — militarized pastoral nomads like the Xiongnu and the Mongols, China’s most formidable enemies. The Huang He is also known as “China’s Sorrow” because of the misery its devastating floods have caused. The earliest cities, states, and civilizations of East Asia all appeared along the Huang He – the Xia, Shang, Zhou, Qin, Han, and Tang dynasties were all centered there. So for millennia some of the largest populations in the world lived within the Yellow River system and faced the potential of regular flood devastation. Emperors and court officials tried numerous schemes to control these floods, but with little success. The other major river of China is the Yangtze, the third longest river in the world after the Nile and the Amazon. It flows from the Tibetan Plateau nearly 4,000 miles through southern China, until it empties into the sea beside Shanghai. The river’s basin area, about one-fifth the size of China, is home to so many people (almost 500 million) that if the Yangtze valley were a country it would be the third most populous in the world! The Yangtze also has its great bend to the north, a bend that perhaps has been of even greater consequence to Chinese civilization than its Yellow River counterpart. In southwestern China, all the mountainous valleys are arranged in a north-south direction, products of the twisting of the landscape caused by the collision between the Indian and Asian tectonic plates. The great rivers that flow through these Himalayan valleys, like the south-running Brahmaputra and Mekong, all flow from the Tibetan Plateau in the north toward the seas that lap Southeast Asia. The Yangtze would have gone the same way, depriving millions of Chinese people of its life-giving water, were it not for a singular topographical feature called Cloud Mountain. This massive wall of limestone is placed right across the path of the onrushing Yangtze, forcing the river to abruptly interrupt its journey south and turn sharply back to the north. The Chinese attribute the fortuitous placement of Cloud Mountain to the work of legendary emperor Yu the Great, who labored mightily to keep the river in China. Geologists, more accurately, attribute it to a particular quirk in twisting of the plate tectonic collision zone. Either way, without Cloud Mountain, Chinese history would have played out very differently. The societies that emerged in Korea and Japan reflect their participation in an East Asian regional identity that revolved around China. We can talk about the existence of an “Eastern Hemispheric cultural zone” by the beginning of the Era of Agrarian Civilizations, just as we speak about the “East Asian region” as a semi-unified cultural and economic entity today. But Korean and Japanese civilizations never became carbon copies of China. Korea The Korean Peninsula extends from northeastern China and is otherwise surrounded by the Yellow Sea to the west, the Sea of Japan to the east, and the Korea Strait connecting the two seas. The Yellow Sea dividing China and the peninsula is only 120 miles wide at its narrowest point, and if you were to sail from southern Korea to Kyushu in Japan on a clear day, land would never be out of sight. The peninsula is about 85,000 square miles — or about the same size as England or the state of Utah. Most of the land is extremely rugged, mountainous, and heavily forested. This presented the first human migrants to Korea with a host of environmental challenges but also a range of possible settlement sites: a long, sinuous coastline with many microenvironments and marine resources, and many wooded interior environments such as river flats, and mountain valleys with access to forest foods, timber, fresh water, and caves. Geologically, Korea consists mostly of a block of ancient granite that was laid down before the Cambrian era. On top of this are younger rocks — gneiss, more recent granites, and limestone. The limestone has produced large caves that are mostly accessible through fissures and cracks rather than through flat floors and entrances. Although these might have seemed attractive to early human migrants, few of these caves were the right shape or size to become practical dwellings. The ancient granites contain important metals – gold, copper, tin, and iron – all of which were accessed by early Korean states. Korea has been a major gold producer for a very long time. Although Japan is so close, Korea has almost none of the volatile volcanic activity of its eastern neighbor. The only volcano is Mount Baekdu in the far north, which at 9,000 feet is also the highest mountain in Korea. Today the mountain contains an extinct crater filled with Heaven Lake; according to ancient legend, this was home to the gods. From Baekdu in the far north all the way to the southern tip of the peninsula, 70 percent of Korea’s land consists of steep-sided mountains. It is their ruggedness rather than their height that has been so influential: the hills made it very difficult to cross from east to west, allowing cultures and kingdoms to develop in relative geographical isolation from each other. One of these, the Silla Kingdom, grew strong enough in its remote southeastern enclave behind the Sobaek Mountains that it eventually overcame the mountainous terrain to conquer the other kingdoms and establish the first unified Korean state. As with China, rivers have also played a critical role in the emergence of Korean culture. All of Korea’s rivers twist and turn as they cut their way down from the mountains. Six are more than 400 kilometers long, and most of them run west or south. All the great capitals of Korean history have been located along the major rivers of the Taedong (where Pyongyang lies today); the Imjin-Han system (where Seoul is located); and the Kum further south. During the last ice age sea levels were about 400 feet lower than they are today, which meant that much of the Yellow Sea was dry land, and Korea was connected to Japan. Paleolithic migrants were able to walk from China across the Yellow Sea Plain to Korea, and then on to Japan. As temperatures warmed about 11,000 years ago, sea levels rose, sealing off the inhabitants of Japan, and separating Korea from China, except along the northern border. Early Korean people constructed a series of rituals, survival strategies, and ideas about the relationship of families to larger organizations that were products of the geographical context in which they emerged. These influenced their origin stories, such as the legend that Korean history dates to 2333 BCE, when King Tangun (a mythical figure born of the son of Heaven and a woman from a bear-totem tribe) established the first kingdom of Choson, or “Land of the Morning Calm.” The name reflected well the tranquil forest camps, seaside villages, and river terraces of the Choson state. Japan Japanese culture was perhaps even more powerfully influenced by the environment in which it formed. Modern Japan consists of four large islands — Hokkaido, Honshu, Shikoku, and Kyushu — and thousands of smaller ones, with a combined area of roughly 145,000 square miles, which means it is just a little larger than Italy, and a little smaller than California. The 1,500-mile-long chain stretches from cool northern latitudes to warmer southern ones. Cypress Tree by Kano Eitoku, c. 1590, Tokyo National Museum Because the islands are separated from the mainland by several hundred miles of water (120 miles at the closest point), this has fostered a sense of security that has allowed for the emergence of distinct Japanese culture. This isolation also helps explain why attempts to invade Japan were largely unsuccessful. But Japan has never been completely isolated from the cultural influences coming from sophisticated neighboring states like Korea and China. The geographical chain of islands to which Japan belongs is much more extensive than just the Japanese archipelago; it stretches along the northwest edge of the Pacific from the Aleutian Islands in the north all the way to the Philippines in the south. This chain is the product of, and still heavily influenced by, the tectonic forces that shape the surface of the Earth. Japan sits at the intersection of no fewer than four tectonic plates (part of the Pacific region’s “Ring of Fire”) so has undergone regular violent shaping and upheaval. The devastating earthquake of 2011, which generated a massive tsunami, was just one of about a thousand earthquakes that rattle Japan every year! Another product of Japan’s tectonic location is that most of the country consists of geologically young mountains, driven up by these plate collisions. These mountains are steep and jagged, producing fast-moving streams and regular landslides. The tectonic plate boundaries have also spawned volcanoes, the highest and most famous of which is Mount Fuji at 12,388 feet. These rugged and unstable mountain ranges are unsuitable for farming, limiting to settlement patterns, and difficult to climb or cross, so have been serious barriers for internal transportation and communication from the beginning of Japanese history. This led to the emergence of regionally autonomous states in early Japan, and to an early reliance on water transport. The sediment regularly washed from these young mountains joins with rich volcanic soil to create narrow but very fertile coastal plains. Although the plains make up only 13 percent of Japan’s area, their fertility marked them as where the first rice farmers settled, and where the first towns, cities, and states appeared. One of the most important of these plains is the Tsukushi Plain in northern Kyushu. Influenced by nearby civilizations in Korea and China, it became an early center of emerging Japanese culture. Japan’s location between the great mainland continent of Asia and the wide Pacific also creates a distinctive and challenging weather environment. In winter, cold winds blow out of Asia and dump large quantities of snow on the mountains of Japan. In the summer, warm moist air blows in from the south, bringing high temperatures and often torrential rains and typhoons. These weather systems have strongly influenced settlement patterns, and the formidable hurricane-like storms have had enormous historical consequences. Two attempted invasions of Japan by the Mongols were thwarted by powerful storms and strong winds that the Japanese considered divine, calling them kamikaze! Because of its long north-south stretch and varied terrain, Japan also contains a wide variety of plants and animals. The combination of plentiful fresh water and a long growing season created a paradise for plants, and for the herbivores that feed off them. When foraging humans first crossed the land bridges connecting the Japanese archipelago to the Asian mainland about 35,000 years ago, they found a rich variety of potential foodstuffs awaiting them — forest and sea food, along with plentiful boar, deer, and many smaller animals. Land and Climate Shape Civilization All these naturally occurring geological, geographic, and biological features — the flooding rivers, towering mountains, arid deserts, and rich alluvial plains of China; the narrow coasts, rugged mountains, and fast flowing rivers of Korea; and the violent storms, earthquakes, volcanoes, and plains of the island nation of Japan — have been as fundamental in shaping East Asian civilization as any products of human ingenuity or will. For Further Discussion How did East Asia’s food and animal sources impact its history? Share your ideas in the Questions Area below. [Sources and attributions]

We're Not in Kansas Anymore By Anita Ravi The development of agriculture led to the creation of cities. Once people figured out how to grow large quantities of food, store it for future use, domesticate animals, and irrigate crops, they could stay put and stop roaming. *The world’s largest cities in 2250 and 1200 BCE. * More people settling in a single place led to more complex societies and cultures. But just what does complex mean? How was life in cities different from life on farms? Let’s first look at where these early cities were located. This map tells me that most of the world’s largest cities were established in the Middle East by 2250 BCE. Scientists have been able to estimate the populations of these cities based on a number of features uncovered at archaeological sites in these areas: How many houses were there? How many rooms were in each house? How big were the food storage rooms? And how many kilns or stoves were in each location? In Cynthia Stokes Brown’s essay, Agrarian Civilizations: Introduction, she argues that all early agrarian civilizations shared some important characteristics. They all had monumental architecture: that is, grand buildings that screamed: “Look at us! We are great!” They all developed a social structure in which an elite helped organize and rule society, while others became specialists (merchants, pottery makers, fishermen), and the majority of the population remained farmers. They all developed systems of writing. It is through writing and the things they built that we can learn about what humans did and the things that were important to the inhabitants of Earth’s first cities. So what do artifacts and written documents from these places tell us about life in cities? What we can learn about early cities from archaeological evidence The first artifacts I will look at to figure out what they might tell me about city life are the Olmec heads (image on the following page). Why these? They are actually the earliest artifacts we have from Mesoamerican cities, which, by the way, are not represented in the map on the left. These heads were created around 900 BCE, which is much later than the foundation of the first cities in Afro-Eurasia. In fact, after a bit more research on the Olmec, I learned that their civilization was the first in Mesoamerica, founded around 1400 BCE. Based on my earlier research into early farming sites, I knew I would also be able to find artifacts of more complex societies in Mesoamerica because evidence of corn crops was also found there, and a precondition of early cities is complex agriculture. These heads can tell us a lot about the early Olmec civilization. The first piece of evidence I can uncover is that these heads were made from stone. Based on the facial features, I can conclude that these are statues of Olmec people and not their god or gods. How do I know that? I am drawing this conclusion based on the fact that these heads are not all the same. It also looks like they have some sort of helmet on and the helmets are decorated differently. The second thing we know is that the heads are quite large, as big as 20 feet high and 20 feet wide. Since they are made of stone, this means they are quite heavy. My research also tells me that the stone used to make these heads came from the Tuxtla Mountains, which are about 60 miles away from the closest Olmec city. According to Michael Coe, an archaeologist who worked at one of the most important Olmec cities, these ancient artists chose some of the large boulders from the bottom of these mountains to make these heads. We still have no idea whether the heads were carved near the base of the mountains, or moved back to ceremonial platforms and carved there. And how did they transport these heavy boulders? I know that there were no native beasts of burden in this area of North America. There were no horses or mules, which were brought by the Spanish and Portuguese hundreds of years later, and no llamas. There is a river about 25 miles from the mountains that flows down to one of the Olmec cities, but there is no evidence of carts with wheels on which to haul these boulders. So just getting these boulders across 60 miles took tremendous time and effort. Olmec heads Why does this matter? What can these heads tell us about how complex life had become for the Olmec? First, a large group of people had to travel to the mountain on foot, and then sever boulders from the mountains using tools. These boulders then had to be transported from the mountains to the river and down the river to the city. It is estimated by Coe that it would take up to 2,000 people to carry the colossal heads over-land. After the boulders were delivered to the carving site, a group of stone craftsmen had to design and carve the heads, again using tools specifically designed for this purpose by toolmakers. Once the heads were carved, they then had to use some form of technology to lift the heads onto the platforms. The manpower and time dedicated to producing the stone heads tells me that the Olmec were doing well enough that they could spare hundreds of men to do this work, and that there would be enough food for these men on their journey to and from the mountains. The heads were clearly valued by the elite, and possibly the clergy, because they had to organize this whole effort. Stone carvers, toolmakers, laborers, artists, rulers, and religious clergy all had to work together to make this happen. The heads tell us that Olmec society had evolved to create these specialized roles and that in order to function effectively, they had to cooperate and work together. What we can learn about early cities from written texts In addition to monuments like the Olmec heads, we are fortunate to have written texts from many of these early cities. In Agrarian Civilizations: Introduction, Stokes Brown argues that writing probably developed as an early accounting system in order to keep track of trade. Symbols were developed to represent different things and people, and in some cultures, alphabets then replaced those symbols. Early texts were written on stone tablets and sometimes etched on the walls of caves. Some of the earliest texts in existence come from the Middle Eastern civilization of Mesopotamia. Scribes in ancient Sumer, where one of the first cities in the world was located, wrote the passage below. So that the warehouses would be provisioned that dwellings would be founded in the city, that its people would eat splendid food... that acquaintances would dine together, that foreigners would cruise about like unusual birds in the sky... At that time, she filled Agade...with gold, Delivered copper, tin, and blocks of lapis lazuli to its storehouses... Its harbor, where ships docked, was full of excitement... Its king, the shepherd Naram-Sin, rose like the sun on the holy throne of Agade... Its city wall touched heaven, like a mountain... Ships brought the goods of Sumer itself upstream [to Agade], The highland Amorites, people ignorant of agriculture, Came before her there with spirited bulls and spirited bucks, Meluhhans [from the Indus valley, and] people of the black mountains, Brought exotic wares down to her... All the governors, temple administrators, and land registrars of the Gude’ena Regularly supplied monthly and New Year offerings there. (qtd. in Chapman16) This is a remarkable document. Let’s start with the title: The Sumerian Goddess Inanna Looks After the City Agade. The title alone tells me that 1) A religion had developed among the Mesopotamians; 2) The goddess mentioned here is interested in protecting the city of Agade and making sure it prospers. The first few lines of the document mention “warehouses,” “dwellings,” and “splendid food.” These words suggest to me that this was a wealthy city, a place of abundance. The fact that warehouses are mentioned tells me that they had lots of things to store, or rather, they had more than they needed. The goddess is credited with filling those warehouses with precious items such as gold, copper, tin, and lapis lazuli (a type of stone). Each of these items had to be mined from the ground and then refined into something usable, which tells me that mining had been developed. The text goes on to mention trade and the presence of “foreigners:” “The highland Amorites” and the “Meluhhans” from the Indus Valley. The harbor, where ships docked, is also mentioned and from the line “full of excitement,” I can gather that it was a busy port. I am thinking that people came to the city of Agade from towns close by and far away for trade and to make offerings to this goddess. The final sentence tells me that all of these people came with “offerings” monthly and for the New Year. Agade must have become a center of religious worship and, it seems, a center of trade and exchange. People from other cities and other places also worshipped this goddess and traveled by sea and land to come to Agade to celebrate and worship there. The second text I am going to look at is a code of law called Hammurabi’s Code and it is also from Mesopotamia. We now refer to this document as the very first code of law developed by man, and it was developed for the city of Babylon. Hammurabi’s Laws Seek To Uphold The Social Order In Babylon (About 1700 BCE) 1. If a man accuses another of murder but cannot prove it, the accuser shall be put to death. 8. If a man steals, he shall repay thirtyfold. If he hasn’t the money, he shall be put to death 15. If a man helps a slave to escape from the city, he shall be put to death. 117. If a man sells his wife or child to settle a debt, they shall work in the house of the buyer for three years, and regain their freedom in the fourth My first reaction upon reading this brief excerpt of Hammurabi’s Code is that the law was harsh in Babylon! They had absolutely no problem with the death penalty. The title of this document tells me that these laws are meant to uphold the “social order,” meaning these are laws that help resolve issues among the people of Babylon. If you lived in Babylon then you could be “put to death” for stealing, helping slaves escape, and falsely accusing someone of murder. The first law — false accusation of murder – is interesting because it relies on the use of evidence: if you’re going to accuse someone of murder, you have to have evidence they did the crime. If you didn’t have adequate evidence, you would be “put to death.” The second law listed above tells me that, in Babylon, you could be forgiven for stealing if you could pay back the person you stole from at a rate of 30 times the value of what you stole; however, if you didn’t repay what you stole, you would be “put to death.” It is also interesting that a man could sell his wife or child to settle a debt, which tells me that women and children had monetary value and no real rights of their own. Slavery was clearly a core part of the social structure since a person could be “put to death” for helping a slave escape. Listed below are a few more laws from the Code: 129. If a man’s wife is caught lying with another man, they shall be bound and thrown into the water. If the woman’s husband spares her life, the king shall spare the life of the man. 132. If the finger has been pointed at a wife because of another man, though she has not been caught lying with him she shall throw herself into the sacred river for her husband’s sake. 141. If a wife goes out, plays the fool, ruins her house and belittles her husband, he may divorce her; or, if he prefers, he may marry another and keep the former wife as his maidservant 142. If a woman hates her husband and says: “You shall not have me,” her past shall be inquired into. If she had been careful and was without past sin; and her husband had been going out and greatly belittling her, she has no blame. She shall take her dowry and go back to her father. 145. If a man’s wife does not give him children, he may take a concubine. These laws all deal with marriage relationships and more specifically, cheating, lying, and bearing children. I guess we could call this the earliest form of divorce law. I find number 142 the most interesting of this set. It says that a woman can leave her husband if she “hates him” and is “without sin,” if he’s been going around badmouthing her.Yet the other laws in the set give her no rights. In fact, if she is even accused of adultery by another man, she has to “throw herself into the sacred river.” It is interesting to me how these very early laws seemed so focused on specific behaviors between women and men. It tells me that the men who wrote these laws were really micromanaging relations between women and men, with an eye toward the hyper-regulation of women’s activities in order to maintain the social order. Listed below are a few more laws dealing with relations among men: 195. If a man strikes his father, they shall cut off his hand. 202. If a man strikes the cheek of his superior, he shall receive sixty strokes with an oxtail whip. 204. If a common man strikes a common man on the cheek, he shall pay ten shekels of silver. 205. 205.If a man’s slave strikes the son of a gentleman on the cheek,they shall cut off his ear. (qtd. in Chapman18) These four laws very clearly maintain a social structure in which people must respect their elders and bosses. Also, there are different consequences for stepping out of line if you are a “gentleman” versus a “common man.” The “gentleman” gets a small fine for hitting someone from a lower class than him. The “slave” gets an ear cut off for hitting the “son of a gentleman.” I imagine if a slave hits the gentleman himself, he’s probably put to death. What does Hammurabi’s Code tell me about the complexity of early cities? The specific details outlined in the excerpts above tell me that a very elaborate legal system evolved by 1700 BCE in Babylon to help regulate relationships among the thousands of people who lived there. The elite who wrote the code were very concerned with maintaining a social order that included “gentlemen,” “common men,” women, slaves, and children. The fact that death was a common punishment in this code of law tells me this was a culture obsessed with making sure no one stepped out of line Conclusions about complexity and early cities What do the documents from Mesopotamia and the Olmec heads from Mesoamerica tell me about life in the world’s earliest cities? Overall, religion and laws were designed by humans to create order in daily life. Whether it was through giving thanks to the gods for wealth or mediating relationships between men and women, a key component to early cities were these man-made systems of order. These laws were probably written by a small group of elites who rose to rule these cities, and maintaining asocial hierarchy was extremely important to them. They were undoubtedly prosperous and wealthy, and thus naturally interested in staying at the top. So the legal and social systems they created did exactly that. The celebration of life through the arts, literature, and religion were also important components of early cities. As people were freed from the daily grind of farming for existence, they sought ways to express their creativity and to celebrate their success. Art and architecture were expressions of that success. This short journal entry is an example of how historians go about exploring important questions and looking at new information. They use a mixture of historical documents and the writings of other historians to inform their thinking. All sources are listed in the working bibliography. [Sources and attributions]

Endurance in the Fertile Crescent The Fall of Jericho from Gates of Paradise, by Lorenzo Ghiberti © Bill Ross/CORBIS By Craig Benjamin Jericho, located in the West Bank region of the Middle East, is the oldest continuously inhabited city on the planet. History and Environment Jericho’s 14,000-year survival is a direct result of biological and geological advantages that explain why a settlement was established there in the first place. This essay explores the idea that the history of a place is just as much about its physical environment as it is about superior technology or government. Big historians, who are interested in the appearance and development of the first agrarian civilizations, ask probing questions: What were the geographical and biological advantages favoring certain regions that facilitated the appearance of the first towns and cities there? What role did climate play in allowing for agrarian civilizations to appear in some regions, while others remained better suited for foraging? And why is it that, while some agrarian civilizations seem to have abused their environments, and thus sowed the seeds of their own destruction, others were able to husband the advantages provided by geography and biology and successfully sustain themselves for thousands of years? To illustrate this critical relationship between history and its environmental context, we use the city of Jericho as a case study. Jericho is the oldest city on the planet, situated today in the West Bank region of the Middle East. The location and long-term survival of the city is an excellent example of the impact of the environment on human history. The establishment of Jericho 14,000 years ago resulted from the same geographical and biological factors that led to the most significant revolution in all human history — the appearance of agriculture. To remind ourselves just how revolutionary this transition was, let’s consider the situation some 15,000 years ago. Humans had by then occupied every continent on the globe except Antarctica. Every single human, wherever they lived, survived by foraging, also known as hunting and gathering. Humans had invented a wide array of foraging techniques specifically adapted to different environments, which ranged from the deserts of Australia to the Arctic ice. But the small size of most foraging bands, and the fact that few exchanges took place between them, limited the amount of collective learning that went on. Hisham Palace in Jericho © Atlantide Phototravel/CORBIS But then something changed! Between 11,000 and 10,000 years ago, new lifeways and technologies associated with farming began to appear. Farming eventually gave humans access to more food and energy; consequently, humans began to multiply more rapidly and live in larger communities like villages, towns, and eventually cities. These processes led to an entirely new level of complexity in the human condition. The transition to agriculture was the first step in a cultural revolution that utterly transformed human societies and drove our species onto a path that led rapidly toward the astonishing complexity of the modern world. And one of the most significant steps in the early stages of that process was the emergence of large settlements like Uruk and Tenochtitlan — and Jericho. To explore the history of Jericho we need first to take a look at the role of climate change in encouraging humans to make this transition to farming, particularly in the Fertile Crescent. Then we need to consider the Natufian people, who were some of the first humans to adopt farming and also were the founders of the small foraging base that went on to become the city of Jericho. Next we need to ask, why there? What particular geological and biological advantages did Jericho have that not only explain why it was established where it was but also account for its longevity? We conclude with a closer look at events in Jericho, further evidence of the importance of environmental factors in the rich tapestry of human history. The Role of Climate Change As we have seen elsewhere in the course, of all the factors that help explain the transition to agriculture and the appearance of large settlements, the most critical is the climate change that occurred at the end of the last ice age. It was only with the end of the last ice age early in the Holocene epoch, some 13,000 years ago, that the first evidence of farming begins to appear in the archaeological record. Conditions were warmer and more stable; entire landscapes were transformed. Forests spread across the steppelands, displacing the large animal species, such as mammoths and bison, that had grazed there. As the herds of these big animals that humans had hunted for tens of thousands of years migrated northward, communities became dependent on smaller game like boar, deer and rabbit, as well as on new root and seed plants. These changes were especially notable in the Fertile Crescent, an arc of high ground that stretches north up the coast of the eastern Mediterranean, east through the mountains of Turkey and northern Iraq, and then south along the high ground between Iraq and Iran. All across the Fertile Crescent, the change in climate encouraged the spread of small game and warmth- loving cereal grasses. Abundance was particularly great in regions where there were good supplies of water, of course, and also where the local environment had produced a range of plants and animals that were good potential domesticates. These same locations attracted humans, too, and we have evidence of numerous Stone Age foraging communities that were experimenting with these plants and animals. The most important of the groups attracted to the abundance of the Fertile Crescent was the Natufians. Natufians and the “Trap of Sedentism” From about 11,000 years ago, some groups of humans began to adopt less nomadic lifestyles, becoming at least “part-time” sedentary. There were two main reasons for this: climate change and local population pressure. With the arrival of more stable climates at the end of the last ice age, regions of natural abundance appeared where large numbers of humans were able to settle. These people were not farming, but living off the rich natural resources of the land. Those communities that abandoned nomadism but still lived as foragers are called “affluent foragers,” or wealthy hunter-gatherers, meaning those who have enough resources to settle down and stay in one place. The most important affluent foragers in the story of Jericho were the Natufian people, who began occupying the western Fertile Crescent (present-day Israel, Jordan, Lebanon, and Syria) just over 14,000 years ago. Evidence for the Natufian culture first came to light in 1928 with discoveries made in northern Israel by Dorothy Garrod at a place called Wadi en-Natuf (hence the name Natufian — we have no idea what they called themselves). We do know that they lived in villages, harvested wild grains, and hunted gazelles. The Natufian toolkit was not really any more sophisticated than that of other foragers, but their more intense use of stone sickle blades to harvest large quantities of wild cereal grains is evidence of a serious change in food-gathering practices. The grain they harvested was also subject to much higher levels of processing than ever before. Many Natufian sites show that standard mortars and grinding stones were supplemented by much larger pipe-shaped mortars dug deep into the bedrock. The construction of regular cemeteries also separates the Natufians from their contemporaries, because they suggest more complex communities with leaders and social hierarchies. Some individuals were buried wearing personal adornments like caps, bracelets, and garters, which look like indicators of their higher status. It’s also worth noting that only a tiny minority of the population were selected for ceremonial burial, which reinforces this idea that Natufian society was more socially stratified than any earlier human community. Evidence that the Natufian diet consisted mainly of harvested and prepared cereal grains was discovered at the important Ain Mallaha site in Syria. Skeletal remains showed that most of the residents had suffered from rotten teeth as a result of eating too much barley and wheat. Ain Mallaha also shows that affluent foraging was leading to increasing populations. Although the site’s estimated year-round population of 200–300 people might seem tiny by today’s standards, this may well have been one of the largest human communities that had ever existed up to that time. This tells us that one of the most important impacts of affluent foraging is that population pressure was forcing humans into smaller territories and denser settlements. By 10,000 BCE foragers had migrated to most parts of this region, and in some areas there was simply not enough room for them all to settle. With each group having to survive off smaller and smaller parcels of land, these communities found themselves caught in what big historian David Christian has called the “trap of sedentism.” Traditional foraging lifeways are almost always nomadic, requiring near constant migration, so human communities had to keep populations small. It is impossible for migrating bands to support too many feeding infants or less mobile elderly members. Survival necessitated not only natural birth control but also killing off unwanted infants and the elderly to keep populations sustainable. Once groups like the Natufians decided to remain in one place through the pursuit of affluent foraging, all this changed. There were no longer the same constraints on population. Older members of the community did not have to be abandoned; more children could be supported. As a result, affluent foraging groups began to increase in size, and this led to the problem of overpopulation. This is, in fact, what we find at most Natufian sites — clear evidence of population pressure. Eventually there were simply too many mouths to feed by foraging practices, which is what archaeologists have found at the site of Ain Ghazal on the outskirts of Amman, Jordan — a rapid fourfold increase in population around 9,000 years ago. This created so much pressure that increasingly desperate and environmentally unsustainable attempts were made to increase food supplies. The result at Ain Ghazal and so many other sites was that groups were forced to leave the settlement to try and survive elsewhere. At a handful of more sustainable sites, however, agriculture did prove capable of supporting much larger populations, once the inhabitants learned to domesticate certain plant and animal species and increase their production through full-scale farming. One such site was Jericho. The Environmental Advantages of Jericho’s Site The ultimate significance of this transition to farming is that eventually sedentism led to the creation of larger settlements, until towns, cities, states, and empires appeared on the surface of the Earth for the first time. But cities and states emerged only in a handful of regions that possessed enough favorable environmental factors to allow for the establishment of these large communities. Rather than thinking of the emergence of cities and states as an inevitable outcome, we need to focus on the particular natural reasons that allowed some villages to continue to grow until they became towns and cities. There are many examples of villages that did grow especially large, although the reasons are not always clear. Some may have become important ritual centers of great spiritual significance. Others had access to a critical resource, such as a reliable water supply. Yet others became important commercial centers because they controlled the trade in valuable goods, or they occupied a strategic site on important migration routes. Jericho has proven itself remarkably sustainable because it benefited from several of these advantages, most importantly a very favorable environment. Jericho is located in the Jordan River Valley in modern Palestine. At an elevation of 864 feet below sea level, Jericho is not only the oldest city on Earth but also the lowest one. The city is well known in the Judeo-Christian tradition as the place where the Israelites returned from slavery in Egypt under the leadership of Joshua. According to the Bible, the walls of Jericho came crashing down after the Israelites unleashed the devastating sound of ram’s horn trumpets, a story we will return to in a moment. But it is the natural walls surrounding Jericho that are of even greater importance in the story of this most ancient of cities. The geological walls of Jericho were created by seismographic activity so intense that it tore a great rift in the Earth’s crust extending all the way from Palestine to northeastern Africa. Of course, the engine that drives plate tectonic movements such as this, and that forces entire continents to move about the surface of the Earth, is the heat trapped deep inside the planet, heat that can be traced back to the processes that created the Earth and Solar System in the first place, heat that can ultimately be traced back to the energy generated in the Big Bang itself! A painting of Jericho by David Roberts © Historical Picture Archive/CORBIS Jericho lies deep in this Jordan Rift Valley, a tectonic feature formed by a fault along the boundary between the African and Arabian plates. As a result of the fault that opened up between these two plates, the land dropped 3,000 feet, eventually settling almost 900 feet below sea level. At this astonishingly low elevation Natufians established the settlement that became Jericho around 14,000 years ago. But we still haven’t answered the question why. What attracted these affluent foragers to this particular location? Again, it is geography and biology that provide the answer. The Jordan River is the only major water source that flows into the Dead Sea, and Jericho is located just a couple of miles west of the river, about 10 miles north of the Dead Sea. The city is well protected by Mount Nebo to the east and the Central Mountains to the west. These geological features form natural defenses because they rise up over a mile in height above the city. Jericho’s location in central Palestine was also ideal for the control of trade and migration routes, which pass up and down this natural valley. Throughout the city’s long history these geographically strategic advantages have made it a source of envy and a coveted possession for a whole series of invaders, many of whom have seen Jericho as the key to controlling Palestine. Despite the importance of these natural defenses and location, by far the most significant environmental advantage Jericho possessed is access to reliable supplies of water. This critical resource, essential for survival in the harsh desert environment, explains the city’s ancient origin and long history. Jericho is located in an oasis and sustained by an astonishingly dependable underground water supply known as the Ain es-Sultan. This natural spring — also known as Elisha’s spring, after a biblical story in the Book of Kings in which the prophet Elisha heals these waters — has apparently never dried up during 14,000 years of continuous human residency. More than 1,000 gallons of fresh water bubble up from the source every minute. Early farmers quickly worked out a system of irrigation canals to disburse this precious resource to the surrounding farmland, which is made up of very fertile alluvial soil. It is this almost unique combination, of natural defenses, strategic location, rich soil, abundant sunshine, and, most of all, plentiful water, that has made Jericho such an attractive and sustainable place for foragers and farmers alike for so many thousands of years. When we tally up this list of environmental advantages it’s hardly surprising that Jericho has enjoyed the sort of long and rich history that it has. The Human History of Jericho Archaeologists have discovered at least 20 successive layers of settlement at the site of Jericho. Kathleen Kenyon was the first to extensively investigate using modern techniques, back in the 1950s. She was searching for the Bronze Age city named in the Hebrew Bible as the “city of palm trees,” but her excavations quickly revealed evidence of occupation dating back many thousands of years before the Bronze Age. Her trenches reached the remains of an early farming settlement about six acres in area, dated to circa 9600 BCE. Continued excavations revealed even earlier layers, proving that the site had been first occupied, most probably by Natufian foragers, as early as 12,000 BCE. This made Jericho the oldest continuously inhabited settlement in all human history. A Neolithic plaster sculpture excavated in Jericho by Kathleen Kenyon © Nathan Benn/Ottochrome/CORBIS After the original foraging settlement, evidence showed that early farmers had learned to domesticate emmer wheat and barley. The availability of these two cereal grains is another significant biological advantage enjoyed by this region. Of the hundred or so domesticated plants humans depend upon today, wheat is one of the most important. It is a superb example of a species genetically pre-adapted for domestication. It can grow in a wide range of environments, and it can generate new diversity at an incredibly rapid rate, which accounts for its tremendous global success as a food crop. Domesticated emmer wheat rapidly spread from the Fertile Crescent all across West Asia until it was replaced in the Bronze Age by free-threshing wheat. Today our planet produces over 620 million tons of wheat each year, providing roughly one-fifth of all the calories consumed by the 6.5 billion members of the human community. Over the thousand years between 8350 and 7350 BCE, the village of Jericho evolved into a town that was home to perhaps 3,000 farmers. They lived in mud-brick houses arranged without any obvious evidence of town planning. Subsequent residents learned to domesticate sheep and also developed a cult of preserving human skulls and placing shells in their eye sockets. Later farming communities were more socially complex and better coordinated than their predecessors. The residents now lived in rectangular shaped buildings made of mud bricks resting on stone foundations. In each of these buildings a number of rooms were clustered around a central courtyard. One room was usually larger — the living room — while the rest were small and probably used for storage. Kathleen Kenyon believed that one particularly large room she excavated may have been a shrine where some type of sacred object — perhaps a pillar of volcanic rock she found nearby — was worshipped in a niche in the wall. Archaeologists working in these later agrarian layers have discovered farming implements like sickle blades, axes, and grindstones; eating vessels including dishes and bowls made from limestone; spinning whorls and loom weights for weaving textiles; and extraordinary full-sized plaster human figures that must have been associated with some sort of religious practice. Eighteenth-century engraving of the Israelites tearing down the walls of Jericho © Bettmann/CORBIS After more than 10,000 years of continuous occupation, Jericho reached its apex in the Bronze Age, between 1700 and 1550 BCE. A class of chariot riding elites dominated and defended the city during an age of widespread intercity conflict across much of Palestine, or the “land of Canaan,” as it was then called. The defenses were based upon a massive stone wall, but even this was not strong enough to prevent disaster; evidence shows conclusively that around 1550 BCE the ancient city of Jericho was destroyed. For more than a century, archaeologists and biblical historians have debated the question of whether this destruction might be evidence of the Battle of Jericho. This is described in the Book of Joshua as the first battle fought by the Israelites in their campaign for the conquest of Canaan. In the biblical account, Joshua’s army marched around the city walls for seven days. On the seventh day the priests sounded their ram’s horn trumpets, the Israelites unleashed a mighty war cry, and the walls of Jericho collapsed, killing every man, woman, and child in the city. An illustration of King Nebuchadnezzar of Babylon © Bettmann/CORBIS According to biblical chronology, this battle would have taken place in 1400 BCE, but modern archaeologists date (with 95 percent certainty) the destruction of Jericho to a century and a half earlier. Because of the discrepancy, modern scholars often dismiss the historical accuracy of the Battle of Jericho, although many biblical historians continue to make claims for its veracity. Despite this calamity, Jericho rose again in the centuries that followed. By the eighth century BCE it had fallen to the Assyrians. The powerful Babylonian king Nebuchadnezzar also conquered the land of Israel and sent tens of thousands of residents into exile. But the exiles were freed soon after by the Persian king Cyrus the Great. Jericho then served as an administrative center for the Persians, and later as a private estate for Alexander the Great, both of whom were attracted to the city by its strategic location and abundant resources. Three centuries later the Hebrew king Herod the Great was granted control over Jericho by the Romans. Under Herod the city flourished as an important agricultural, commercial, and administrative center, and also as a winter resort for Jerusalem’s aristocracy. In the first century of the Common Era, the Greek geographer Strabo described the city’s environmental advantages like this: Jericho is surrounded by mountainous country which slopes toward it like a theatre. It is mixed with all kinds of cultivated and fruitful trees, though it consists mostly of palm trees. It is everywhere watered with streams. In the same century, according to the Christian Gospels, Jesus passed through Jericho, where he healed a blind beggar and inspired the local tax collector Zacchaeus to repent of his unethical practices. After the fall of Jerusalem to the Romans in 70 CE, Jericho entered a period of decline, although it remained an important Christian pilgrimage site into the Byzantine period. In the seventh century Jericho became part of the expansive realm of Islam, and we have another description of the advantages of the city written by the 10th-century Arab geographer Al Maqdisi: The water of Jericho is held to be the highest and best in all Islam. Bananas are plentiful, also dates and flowers of fragrant odor. During the Crusades, Christians occupied the city until they were driven out by Saladin (the leader of the Arab and Muslim opposition to the Crusaders). Throughout the long reign of the Ottomans, from 1517 to 1918, Jericho slowly shrank to the size of a village and was regularly raided by Bedouins. In the 20th century Jericho was controlled at various times by Britain, Jordan, Israel, and the Palestinians. Today Israel and the Palestinian Authority continue to argue over the status of Jericho, and the future of the city and its 20,000 residents is anything but clear. Physical Endurance The history of Jericho is rich and complex, punctuated with the same parade of triumphs and tragedies that so many other ancient cities have experienced. But Jericho’s status as the most ancient city on Earth makes it unique. This longevity strongly supports the idea that history is ultimately as much about the physical environment in which it takes place as it is about technology or leadership. At the end of the last ice age the Fertile Crescent was favored with an array of natural advantages, which explains not only the emergence of agriculture but also that of the first villages, towns, and cities. These same advantages of geography, flora, fauna, and climate made it possible for the Natufians to establish a small foraging community deep in the tectonic fault of the Jordan Rift Valley, surrounded by natural defensive walls, and blessed with rich soil and a seemingly endless supply of fresh water, that easily transitioned into a thriving agricultural community. The history of Jericho is a 14,000-year-long reminder that the story of humanity can really be understood only if it is embedded deeply into the natural context in which it has played out, for the environment is truly the great physical stage upon which our human drama continues to unfold. For Further Discussion Did many of the civilizations that you’ve read about so far overcome agricultural and geographical challenges? Share your answer in the Questions Area below. [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. First read: skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Second read: understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: How did Ibn Bassal's pilgrimage to Mecca contribute to the development of agriculture in Al-Andalus?Why was Ibn Bassal's book Diwan al-Filāḥa (Book of Agriculture) significant?How did Ibn Bassal improve the efficiency of farming? What evidence can you see of those developments today?According to the author, the Arab Green Revolution was perhaps the most important event in human production since the agricultural revolution. Why do you think the author makes that claim?Looking at just the images and colors in the graphic biography, what ideas do you think the author could be conveying about agriculture during this time? Third read: evaluating and corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: What does Ibn Bassal's story tell you about the way agriculture expanded collective learning? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. Taking Root: Ibn Bassal - Graphic Biography Writer: Molly Sinnott Artist: Argha Manna Ibn Bassal was a scholar and expert botanist in Al-Andalus. He developed and spread techniques that transformed agriculture throughout Afro-Eurasia. Download the Graphic Biography PDF here or click on the image above.

Scientists are still not sure why humans abandoned foraging and took up farming in several places around the world at about the same time. This gallery highlights where agriculture emerged and what was grown. Global Warming The Big History Project Glaciers continued to advance until about 18,000 years ago. At this point temperatures began to even out and then to gradually increase. Sea levels began to rise. With ice caps at both poles, the Earth is currently in what is called an interglacial period and, technically speaking, still within the "Pliocene-Quaternary glaciation," or ice age. The Stage Is Set for Agriculture As temperatures increased and sea levels rose, two important things happened. Land bridges such as the one connecting Asia and North America were submerged and climates throughout most of the world became more moderate, enabling certain species of plants and animals to prosper. High Water © Tim Thompson/CORBIS The Bering Land Bridge once connected the eastern-most edge of Siberia with what is now the western coast of the Seward Peninsula in Alaska. Until about 11,000 years ago, the bridge was a treeless tundra with shrubs and shallow ponds that served as a corridor between Asia and the Americas, a route used by wildlife and by early humans. Today, the Bering Land Bridge National Preserve in Alaska (shown here looking west) is an impassable wetlands that ends at the 58 mile wide Bering Strait. The Fertile Crescent Agriculture emerged in the Fertile Crescent, a wide swathe of river valleys and rich soils in the Middle East, about 10,000 years ago when humans first cultivated cereal grasses like emmer wheat. The first "farming" was thought to have occurred near Jericho in the West Bank region of present-day Israel and Jordan by a group of people called the Natufians, but full-scale agriculture really took off a bit later in Mesopotamia – a region between the Tigris and Euphrates rivers in present-day Iraq. Agriculture emerged in the Nile River Valley of Egypt shortly thereafter. Big River Valleys Lead to More Agriculture By about 7,000 to 8,000 years ago, agriculture had emerged in other regions of Asia. The soils deposited from large rivers were extremely fertile and proved ideal for the cultivation of cereal crops. Domestication of wheat and barley occurred in the Indus Valley in what is now Pakistan and India. East, in present-day China, millet and wheat (and later rice) was grown in the Huang He (Yellow) River Valley. The Americas Agriculture came later to the Americas but it's important to note that it emerged completely independent of the farming that had already begun on the Asian continent. The rising seas had covered the Bering Land Bridge thousands of years before and humans in the Americas developed agriculture on their own, without contact with humans living in Afro-Eurasia. At about this same time or earlier, agriculture also emerged in the highlands of Papua New Guinea in the Pacific region. Farmers in the Americas cultivated a wild cereal grass called teosinte in Mesoamerica and grew potatoes in the Andes Mountains while farmers in Papua New Guinea grew sugar cane and tubers like taro and yam. Teosinte Joseph Tychonievich/ Greensparrowgardens.com The first Mesoamerican farmers cultivated a wild grain called teosinte and transformed it into maize, an ancestor of modern corn, using artificial selection. In this picture of a recently grown strain of teosinte, the "cob" that we are familiar with is barely present but the telltale  "corn silk" is very prominent. Corn © Tetra Images/Corbis Once maize was cultivated, it became an extremely important part of life in Mesoamerica. It was the primary source of food energy and early communities like the Olmec, Maya and Aztecs considered the prolific grain to be a divine source of life. Modern agriculture transformed maize even further, cultivating innumerable strains of plump, sweet corn for use as food for humans and livestock. Ant Farm? Humans don't exactly have a monopoly on farming. Some types of ants "farm" aphids, protecting them on the plants that the smaller insects eat and then themselves consuming the sugary "honeydew" that the well-fed aphids secrete. Symbiotic (interdependent) relationships like this are not unlike those that we have with our livestock and crops.

The World’s First Big City Sumerian statuette of a priest, c. 3000 BCE© Gianni Dagli Orti/CORBIS By Cynthia Stokes Brown, adapted by Newsela Nestled between the Tigris and Euphrates rivers, the world’s first major city sprang up in a fertile region of land called Mesopotamia. The First City Between approximately 3600 and 2600 BCE, the people of Uruk created the innovations characteristic of cities ever since: social hierarchies, specialized occupations, coercive political structures, writing, religion and literature, and monumental architecture. What is a city? By “city” we mean simply a large group of people, tens of thousands, collected into a whole and living in a defined place with structures designated for a range of specific social functions. To support a city, people living on the land around it had to be able to generate stable surpluses of food from the fertility of the soil and the creatures that inhabited it. In addition, people in the city had to devise ingenious ways to distribute those surpluses, ways that would reinforce constructive patterns of conduct and practice. Cities began to emerge about the same time in various places around the world. But most archaeologists agree that it is fair to claim Uruk (pronounced OO-rook) as one of the world’s first cities (Uruk is its Akkadian name; its own people called it Unug; the Hebrew Torah called it Erech; and its current name, Warka, is Arabic.) Uruk arose about 5,500 years ago, no time at all when measured against the more than 200,000 years of Homo sapiens or the 6 million years of hominin evolution. Location, Location, Location Uruk arose in the place now called Iraq, about 150 miles south of modern-day Baghdad. Greek historians called this area Mesopotamia, or “the land between the rivers.” Those rivers were the Euphrates to the west and the Tigris to the east, both of which flowed from the Taurus Mountains in Anatolia (now Turkey) in the north down to the Persian Gulf in the south. Sumerian ruins of Uruk© Nik Wheeler/CORBIS By roughly 4000 BCE people living in higher places in what is now Iraq had settled down to care for domestic sheep and goats and to grow wheat, barley, and peas. Yet their climate was changing; less rain was falling, and they needed to move to more stable sources of water. Detail of a cuneiform tablet from Tello in southern Mesopotamia© Gianni Dagli Orti/CORBIS As people migrated into the two river valleys, they found that the soil produced abundant crops due to the fertility of topsoil from repeated flooding of the rivers. They could grow enough to store surplus grain, enough to support other individuals with occupations other than farming. The surplus grain needed to be collected and distributed; probably priests first managed this task. In addition to grains and domestic animals, people had plenty of fish and fowl from the river and marshes. Beer had already been invented, and a goddess of beer, named Ninkasi, was worshipped. Writing, Beliefs, and Everyday Life A great deal is known about Uruk because of excavations of the site beginning in 1850 and because the earliest writing in the world comes from there, dated to about 3500 BCE. People in Uruk wrote on clay tablets with reeds. The writing is called “cuneiform,” named after the wedge-shaped reeds that writers pressed into wet clay. Since clay tablets are more durable than the silk, bark, bamboo, or papyrus used by other people for writing, many of Uruk’s tablets have survived and are now held in museums throughout the world. From inscriptions found in Uruk we know that its people built a temple to a sky god called An and another one to his daughter, Inanna, goddess of love and war (later known as Ishtar). Inanna served as the patron goddess of Uruk; its inhabitants believed that they attracted her there by building a special house for her, staffed with priests and servants. The priests managed the people’s contributions and gradually built up their power, using temples as centers for the redistribution of surplus food. As people learned to farm, they changed their clothing from wild-animal skins to what they could make from their domesticated animals and plants. In Mesopotamia this meant that most people wore woolen garments made from the fleece of their sheep, even in hot weather. Only the elite could wear linen, a textile made from the fibers of flax plants, because the process of making it took much longer than weaving or knitting wool. Uruk at Its Height By 5,000 years ago Uruk held 40,000–50,000 people, and after another few hundred years it reached its peak of 50,000–80,000 inhabitants. By that time there were 11 other cities between the rivers, and they engaged in frequent warfare with each other over land, water, and other resources. Priests gradually had to share their power with warrior leaders, a system that eventually evolved into a single king ruling each city. Early clay tablets in Uruk contain a “standard professions list,” which listed a hundred professions from the king down through ambassadors, priests, and supervisors and on through stonecutters, gardeners, weavers, smiths, cooks, jewelers, and potters. The social structure was topped by a small ruling and priestly elite, with a much larger group of commoners who either owned property or did not, and a bottom small group of slaves, those who were captured in war, convicted criminals, or people heavily in debt. As a single authoritarian ruler emerged to lead Uruk and its surrounding farms and villages, historians say that the first state emerged almost simultaneously with the first city. The state consisted of powerful elites who could coerce labor and tribute. Why did the majority of people allow a few people so much power? This is difficult to answer, but on the one hand it seems that the elites took power as more resources became available. On the other hand, it seems that citizens gave power in exchange for organization, which permitted large-scale projects like irrigation, and for security and protection. What may have begun as consensual power may have evolved into coercive power as elites accumulated more resources. Writing began in Uruk as a way to keep track of how many sheep, goats, and measures of grain passed through the central warehouses. It began with pictures made in wet clay representing the various goods. After about 400 years people had figured out how to use symbols and abstract numbers instead of drawing a picture for each item. They used a small wedge to represent one, a small circle to represent 10, a large wedge for 600, and a large circle for 3,600. Their system of numbers was based partly on 10 and partly on 60 for measuring grain. This latter base-60, or “sexagesimal,” system led to viewing a circle as 360 degrees. After about a thousand years, people in Uruk had developed their system of writing sufficiently to compose hymns, funeral songs, and superhero epics. Here are some lines from “The Lady of the Evening,” a hymn to the evening star, which represented Inanna (Sumer refers to the area where people spoke Sumerian, from the vicinity of modern-day Baghdad down to the Persian Gulf): At the end of the day, the Radiant Star, the Great Light that fills the sky,The Lady of the Evening appears in the heavens.The people in all the lands lift their eyes to her...There is great joy in Sumer.The young man makes love with his beloved.My Lady looks in sweet wonder from heaven.The people of Sumer parade before the holy Inanna.Inanna, the Lady of the Evening, is radiant. I sing your praises,holy Inanna. The Lady of the Evening is radiant on the horizon. (Wolkstein and Kramer, 1983) Poets in Uruk also gave us our first superhero story — in fact, our first recorded story of any kind — The Epic of Gilgamesh. The tale imagines Gilgamesh, a king who may have actually ruled Uruk at about 2750 BCE, as 2/3 divine and 1/3 human. He has a friend, Enkidu, who becomes citified and stops living as a wild hunter. They go on many adventures together, one of which results in Enkidu being condemned to death, and Gilgamesh has to accept the loss of his friend. This beautiful story has several modern versions. Here are a few lines describing the city of Uruk: When at last they arrived, Gilgamesh said to Urshanabi [the boatman], “This is the wall of Uruk, which no city on earth can equal. See how its ramparts gleam like copper in the sun. Climb the stone staircase, more ancient than the mind can imagine, approach the Eanna Temple, sacred to Ishtar, a temple that no king has equaled in size or beauty, walk on the wall of Uruk, follow its course around the city, inspect its mighty foundations, examine its brickwork, how masterfully it is built, observe the land it encloses: the palm trees, the gardens, the orchards, the glorious palaces and temples, the shops and marketplaces, the houses, the public squares.(Mitchell, 2004) When at last they arrived, Gilgamesh said to Urshanabi [the boatman], “This is the wall of Uruk, which no city on earth can equal. See how its ramparts gleam like copper in the sun. Climb the stone staircase, more ancient than the mind can imagine, approach the Eanna Temple, sacred to Ishtar, a temple that no king has equaled in size or beauty, walk on the wall of Uruk, follow its course around the city, inspect its mighty foundations, examine its brickwork, how masterfully it is built, observe the land it encloses: the palm trees, the gardens, the orchards, the glorious palaces and temples, the shops and marketplaces, the houses, the public squares. (Mitchell, 2004) The Legacy of Uruk and Mesopotamia Despite all the amazing innovations by its people, Uruk faced eventual decline. After Mesopotamia experienced several hundred years of constant warfare, Sargon of Akkad (ruled 2334–2279 BCE) conquered most of it. A serious drought occurred in about 2250 BCE. By 1700 BCE all of southern Mesopotamia had declined into a backwater of other empires. The underlying reasons seem to be environmental. The irrigation that Mesopotamians used to increase their crop yields increased the salinity, or salt content, of the soil. (As the sun evaporated the water standing in the fields, it left the mineral salts that had been dissolved in the water.) As the salinity of the soil increased, the yields of grain, especially of wheat, decreased gradually. By 1700 BCE crops were depleted by as much as 65 percent. Mesopotamia had a new time of glory as Babylonia, under Hammurabi (ruled 1792–1770 BCE) — who had his capital at Babylon, a city about 250 miles northwest of Uruk on the Euphrates River. Hammurabi may be most famous for his Code of Hammurabi, one of the earliest examples of a “written” set of laws. Other empires warred with Babylonia until it had a final moment under King Nebuchadnezzar, who in 586 BCE conquered Judah and Jerusalem and sent at least 10,000 Jewish people into exile in Babylon. This is thought to be close to their original home. According to the Old Testament, Abraham came from the city of Ur, one of the 12 city-states in southern Mesopotamia, located about 50 miles southeast of Uruk. Apparently Abraham left Ur in about the 20th century BCE, in the midst of drought, warfare, and collapse, to travel southwest with his band of followers, eventually to settle in what is now Israel, carrying with them traditions from Mesopotamia. Detail of the stele of Hammurabi© Gianni Dagli Orti/CORBIS Traditions from southern Mesopotamia also were adopted by Greek scholars, who got them from Babylonia. Especially in mathematics, ideas from Mesopotamia persist. Our day is still divided into 24 hours, each hour into 60 minutes, and each minute into 60 seconds. A circle still consists of 360 degrees. Cuneiform writing was used regionally until the beginning of the Common Era, when it disappeared; about 300 current scholars have learned to read it. By 300 CE people had mostly abandoned Uruk, and it was completely empty by the time of the Arab conquests in 634 CE. People in Uruk put together all the pieces of what we call civilization 5,000 years ago. They combined kings, writing, monumental temples and palaces, specialized occupations, and literature into a culture remarkably similar to what we still know, despite the many changes that have occurred since. For Further Discussion Can modern humans “know” the history of a group of people who did not have writing, or can we only really “know” about people who kept written records of their activities and achievements? Share your thoughts in the Questions Area below. [Sources and attributions]

How We Chronicle the Past A Babylonian astronomical calendar, c. 1000 BCE© Science Source By David Christian, adapted by Newsela Although many species note the passing of time, only our own species, Homo sapiens, is capable of sharing accounts, or memories, of past events and turning these into stories or “histories.” What Is History Anyway? As humans discovered ever more precise ways of keeping track of time, so we have also developed more accurate ways of keeping records and recording history. What exactly is history? We could argue forever about that, but let’s just agree that it means “a shared knowledge of the past.” Why is it important to know about the past? How does that help us? Do animals need history? Did our ancestors have a sense of history in the Paleolithic era, and how has that sense changed over time? How Do Animals and Plants “Do” History? All living things carry “memories” of the past. Animals need to be able to keep track of the seasons so they know when to hibernate, when to hunt, and when to have children. Many rodents and birds store nuts and other food in special hiding places, and they need to remember where they stashed them so they can find them months later. Wolves leave their marks on the perimeters of their turf, creating a sort of record that says to other wolf packs: “This is owned by the BHP pack. Keep out!” Even plants seem to record the passing of time. If you slice through a tree, particularly in a region with lots of seasonal changes, you’ll see “growth rings.” Every year a new layer grows just under the bark. There is often a light part formed early in the year and a darker part that forms later, so each ring represents one year of growth. Wet seasons typically produce thicker rings than dry seasons, so dendochronologists — the scientists who study growth rings — can frequently figure out the exact year in which each layer was formed. They can also see evidence of climatic events such as droughts or forest fires. But “tracking the past” isn’t the same as having a “memory” of the past. A tree ring might record the date of a major fire, but the tree wouldn’t respond if I asked, “Do you remember the great fire of 1730?” Only humans can share their knowledge of the past because only humans have a communication system powerful enough to share what they know and learn. The First Histories Growth rings of a tree© Georgette Douwma / Photo Researchers, Inc. We don’t really know when humans first began to share their knowledge of the past. But our understanding of collective learning suggests that they probably did so early on. If we assume, as we have done in this course, that even the earliest members of our species were capable of collective learning, then we must assume that they could share ideas not just about where water holes or lions are, but also about last year’s bush fire, or that fight that took place with the people who live beyond the river, or even of earlier geologic events. All modern foraging societies tell stories about the past, many focused on ancestors, but also on the creation of what’s around us. Indeed, most humans tell “origin stories,” and origin stories count as history because they share ideas about the world. In the beginning the earth was a bare plain. All was dark. There was no life, no death. The sun, the moon, and the stars slept beneath the earth. All the eternal ancestors slept there, too, until at last they woke themselves out of their own eternity and broke through to the surface. This is the beginning of an Australian Aboriginal origin story from recent times. We don’t know if the people who told this story believed it was literally true, but it provided a way of thinking about how things came to be as they are. Here is the same origin story recounting the creation of humans: With their great stone knives, the Ungambikula carved heads, bodies, legs and arms out of the bundles. They made the faces and the hands and feet. At last human beings were finished. It’s very tempting to believe that at ancient sites like Blombos Cave in South Africa, where humans lived and worked and made different colored paints more than 70,000 years ago, they were also telling stories about the past, passing them on from generation to generation and tribe to tribe, and perhaps also illustrating and recording them in some way. History Based on Memory But if there were historians in Blombos Cave, they relied mainly on their memory for the stories of the past, because there were no written records. We know from studies of modern foraging societies that people who cannot write down information rely on such “oral tradition,” and develop powerful ways of remembering. Ancient storytellers could keep telling stories for days, and poets had many techniques to help them recall long epic poems so they could recite them at will. For example, it seems likely that the Greek poet Homer used similar phrases over and over again, such as “the wine-dark sea,” as well as rhymes and regular rhythms, mainly to help him remember his epics. In ancient Greece, Mnemosyne, or the goddess of memory, was regarded as the mother of all nine muses — the various goddesses of literature, art, and science. (The modern word mnemonic, which means “a technique for remembering things,” comes from her name.) And even in societies with writing, memory remained an admired skill. The Roman philosopher Augustine of Hippo had a friend who could recite backward the works of the poet Virgil. In the Muslim world it was commonplace to memorize the entire Koran. People continued to develop ways of memorizing, such as walking in your imagination through a large building in which you had placed objects, each of which helped you remember something special. History Based on Written Records Detail from the fifthth-century Ambrosian Iliad© Heritage Images/CORBIS Today, though, we expect proper history writing to be based not on the memory of the historian, but on evidence, and mostly on written evidence. I think you’d worry if a history teacher said, “Well, I think World War I began in about 1914 because that’s what my grandmother’s dad told her.” History based on written records appears quite late in human history. The first written records date back a little more than 5,000 years in Egypt and ancient Sumer. The earliest Sumerian records were made using reeds cut at an angle to make wedge-shaped (cuneiform) marks on clay, which was then baked hard. Many of these clay tablets survive today, and scholars can still read them. The earliest records look like accounts: lists of property, cattle, sheep, and wheat. But even that is history of a sort, and it’s pretty important because it provides details of who owned what. Within a few centuries, we begin to find elaborate written chronicles, such as the great Sumerian epic of Gilgamesh, the king of Uruk. We also find stories of floods, of gods, and of the creation of the world, some of which made their way into the Jewish scriptures, the Christian Bible, and the Koran. Wherever writing appeared it was used to write accounts of the past. And despite most people not being able to read or write, those accounts started to become the basis for further historical accounts. Written documents began to be seen as more authoritative than oral stories, because once something was written down it was much harder to keep changing the story. The Importance of Evidence As societies became more interconnected and people began to compare different accounts of the past, they became more concerned with a crucial question: Which version is truest? Let’s look at a modern portrayal of human origins: “Our hominine ancestors evolved over several million years. But during the last million years, species appeared with very large brains, and our own species, Homo sapiens, probably appeared about 200,000 years ago. We know this because we have fossil remains of individuals that seem identical to modern humans, and we begin to find evidence of technological innovation and symbolic activity.” I wrote that, but it is typical of today’s history writing because it is so concerned with evidence. Where there are competing versions of the past, you have to give evidence for yours if you want to be taken seriously. We can already see this growing concern with evidence 2,000 years ago in the writings of some of the greatest historians of the classical era, such as Herodotus of Greece and China’s Sima Qian. Both lived in worlds where different peoples made different claims about the past, so both understood the need to base their accounts of the past on evidence wherever possible. Herodotus (c. 484–425 BCE) traveled widely in the eastern Mediterranean as well as to Olbia, on the northern shores of the Black Sea, where he met some of the Scythian pastoral nomads about whom he wrote so vividly. Modern archaeologists have shown that his somewhat gruesome accounts of Scythian royal burials were very accurate. He also described some Scythian origin stories, and he did so with all the skepticism of a modern anthropologist. About three centuries later, the Chinese historian Sima Qian (c. 145–86 BCE) provided lengthy descriptions of the nomadic Xiongnu, who lived north of China, in Mongolia. For example, he wrote that “they move about in search of water and pasture and have no walled cities or fixed dwellings, nor do they engage in any kind of agriculture.” His account was not made up; it was based on the writings and memories of many Chinese travelers who had visited Mongolia, including Silk Road adventurer Zhang Qian, who was captured by the Xiongnu in 139 BCE, and lived among them for 10 years. But it was really from the Enlightenment era, in the 18th century, that the notion of evidence-based history as the most important form of history writing became more prominent. Today, all professional historians understand that their first task is to get the history right. That means checking all the details against hard evidence, and preferably against written documents. The great 19th-century German historian Leopold von Ranke pioneered the modern art of writing history on the basis of detailed archival records. And these days, history based on written documents remains the primary form of historical scholarship. An illustration of Herodotus reading his history by Heinrich Leutemann, 1885© Bettmann/CORBIS But document-based history has some serious limitations. First of all, history based on written documents often only tells us about the lives of the rich and powerful. That’s because until a century or two ago most other people could not read or write, so they weren’t very well represented in the documents of earlier times. Sometimes, archaeology and anthropology can step in by helping us use material objects — houses, clothes, bits of pottery or skeletons — left behind by ordinary people, or by using studies of modern societies that give us some hints about how ordinary people lived in the past. Written records have another serious limitation. They only reach back a few thousand years. When H.G. Wells, just after World War I, tried to write a history of the entire Universe, he complained that “chronology only begins to be precise enough to specify the exact year of any event after the establishment of the eras of the First Olympiad [776 BCE] and the building of Rome [753 BCE].” Only in the middle of the 20th century did we start finding accurate ways of dating events that happened before there were written records. In the 1950s, the American chemist Willard Libby showed how you could use the breakdown of radioactive materials such as carbon 14 to date objects such as bones or food remains that contained carbon. Libby’s work was the beginning of a “chronometric” revolution, as a whole series of new techniques emerged for dating events in the distant past, eventually right back to the Big Bang. Those dates have made it possible for us to write and teach big history. Have We Gotten Better at Studying the Past? Today we have access to better records and more types of evidence about the past than ever before. It is astonishing to think that we can actually say something serious about the origins of the Earth or of the Universe, and we have so much evidence about recent centuries that historians will never be able to use it all. So in some sense it seems that we must be doing history better than our ancestors did. But have there been losses as well as gains in the history of history? Haven’t we lost the vivid, personal sense of engagement with the past that existed in oral cultures where history was always told as a story? Almost 2,500 years ago, in the Phaedrus, Plato described this sense of loss. In this dialogue, Socrates tells how the Egyptian god Thoth, who claimed to have invented writing, bragged that his invention would improve people’s memories. King Thamus (also an Egyptian god) replied that this was nonsense: For this invention will produce forgetfulness in the minds of those who learn to use it, because they will not practise their memory. Their trust in writing, produced by external characters which are not part of themselves, will discourage the use of their own memory within them. You have invented an elixir not of memory but of reminding; and you offer your pupils the appearance of wisdom, not true wisdom, for they will read many things without instruction and will therefore seem to know many things, when they are for the most part ignorant...since they are not wise, but only appear wise.(Plato in Twelve Volumes, sections 275a–275b) For this invention will produce forgetfulness in the minds of those who learn to use it, because they will not practise their memory. Their trust in writing, produced by external characters which are not part of themselves, will discourage the use of their own memory within them. You have invented an elixir not of memory but of reminding; and you offer your pupils the appearance of wisdom, not true wisdom, for they will read many things without instruction and will therefore seem to know many things, when they are for the most part ignorant...since they are not wise, but only appear wise. (Plato in Twelve Volumes, sections 275a–275b) Can it be that both arguments have merit? That speech and memory have distinct, perhaps irreplaceable, advantages over writing, but that writing has both broadened and sharpened our collective memory? A relief depicting Thoth from the tomb of Chamuas in Luxor, Egypt, c. 1200–1085 BCE© Gian Berto Vanni/CORBIS For Further Discussion How has writing been a positive innovation for humans? Does writing have any negative impacts that you can think of? Share your ideas in the Questions Area below. [Sources and attributions]

The Origin of World Religions By Anita Ravi As people created more efficient systems of communication and more complex governments in early agrarian civilizations, they also developed what we now call religion. Having done some research on the common features of early agrarian cities, I’m interested in finding out why all civilizations adopted some sort of religion and how these religions spread over vast regions. I know that by 1200 BCE, there were developed cities in most parts of the world. Having examined some early writing from the city of Sumer in Mesopotamia, I know that people had already conceived of gods that looked out for them and the welfare of their crops and cities. But the world religions I know of — Hinduism, Judaism, Buddhism, Christianity, and Islam — were bigger than a single city or even a single region of the world. In fact, these religions have survived for thousands of years, and all of them seem to have developed around the same time. Since people do not appear to have lacked for religious life on a local scale from very early times, why did several large-scale belief systems emerge between 1200 BCE and 700 CE? In fact, why did all the major world religions appear in that era? Why religions became global One possibility is that by about 100 BCE, the population in Afro-Eurasia had climbed to over a million. As a result of increasing commercial and cultural interaction between people across this large area, religions were shared. The new religious systems provided foundations of cultural communication, moral expectation, and personal trust among people who were meeting, sharing ideas, and doing business with one another far beyond their local neighborhoods. The historians J.R. and William McNeil call this the development of “portable, congregational religions.” Common features of these religions are the following: there is usually a founding man who receives the word of God; there is a key text or set of texts that defines man’s relationship with God; there are recommended ways of living and worshipping; people come together regularly to have God’s word interpreted for them by an authority; and there is a path to self-trans-formation and eternal salvation in one way or another. In The Human Web: A Bird’s-Eye View of World History, the McNeills argue that religion took hold during this time period for the following reasons: In subsequent centuries, urban dwellers, and particularly poor, marginal persons, found that authoritative religious guidance, shared faith, and mutual support among congregations of believers could substitute for the tight-knit custom of village existence (within which the rural majority continued to live) and give meaning and value to ordinary lives, despite daily contact with uncaring strangers. Such religious congregations, in turn, helped to stabilize urban society by making its inherent inequality and insecurity more tolerable. (61) So what they’re saying is that religion provided structure and meaning for large groups of people in ways that small, tight-knit village communities used to do. Religion, especially faiths that were shared by large groups of people, actually provided stability in cities. These religions were accepted by thousands of followers because they appealed to many different people from all social classes and occupations. If the texts and tenets of these faiths spoke to such a wide variety of people then the religious beliefs were more likely to spread along trade routes, unlike the earlier village-based religions. FaithApproximate start datePlace of originApproximate number of followers (2014)Hinduismc. 2000 BCENorthern India979 millionJudaismc. 2000 BCEMiddle East15.6 millionBuddhismc. 500 BCENorthern India480 millionConfucianismc. 500 BCENorthern China6.5 millionDaoism (Taoism)c. 550 BCENorthern China3 millionChristianityc. 100 CEMiddle East2.3 billionIslamc. 622 CEMiddle East1.6 billion While many people were drawn to these early religions, they are not all the same. Each faith has its own answers to questions about humanity and each one has different practices. All faiths, apart from Confucianism, which some scholars classify as an ethical system rather than a religion, offer eternal salvation in one form or another. Judaism, Christianity, and Islam are all monotheistic, with one omnipotent and omniscient deity. Hinduism allows for the worship of numerous, powerful gods and goddesses. Buddhism and Daoism also accept the existence of multiple divine beings in various forms and incarnations. All of these religions teach that human relations should be guided by kindness, selflessness, and decency. Confucianism, in particular, emphasizes public moral behavior, good government, and social responsibility. A closer look at Hinduism and Buddhism So how did each belief system define these relationships with God, with society, and with other humans? First, I’m going to take a look at Hinduism. I learned through a few web searches and from several secondary sources that Hinduism is often called the “oldest religion” mainly because there is no single founder and because the main ideas of the religion appear in a variety of different texts written over time, starting around 4,000 years ago. What’s interesting about Hinduism is that it was developed by a group of people living in the Indus Valley who had a rigid hierarchical social structure called the caste system. Michelle Ferrer sums up the basic tenets of Hinduism in The Budding of Buddhism, which is quoted below. The untouchables, the lowest members of society, dealt with human waste and the dead. This group did the jobs no one else wanted to do. They were regarded by the other groups as ritually impure and therefore outside the hierarchy of groups altogether. The Sudras had service jobs, and the Vaisya were herders, farmers, artisans, and merchants. The Ksatriyas, the second highest caste, were the warriors and rulers. At the top were the Brahmans, who were priests, scholars, and teachers. Because priests were part of this caste, the early religion is known as Brahmanism. Brahmanism evolved into the larger Hindu tradition. The Hindus revered many gods. They believed that people had many lives (reincarnation). Also, they believed in karma. This meant that whatever a person did in this life would determine what he or she would be in the next life. Thus, reincarnation creates a cycle of birth, life, death, and rebirth. The cycle ends only when a person realizes that his or her soul and God’s soul are one. To help achieve this goal, the Hindus had several spiritual practices, some of which are done in the western world today, including meditation and yoga. The Hindus also believed in the Purusharthas: Four Goals of Life. These goals motivated people in their lives: 1. dharma: living a virtuous life 2. kama: pleasure of the senses 3. artha: achieving wealth and success lawfully 4. moksha: release from reincarnation So what this is telling me is that the religion evolved from a social class structure where people had very defined roles. Since the religion hinges on this idea of karma — what you do in life today determines what you do in the next life — I wonder if the untouchables could come back as a higher caste if they “lived a virtuous life.” If I look back to what the McNeills said about religion giving meaning to the drudgery of daily life, Hinduism seems to fit that description perfectly. What’s more, it seems to be an effective system for maintaining a social hierarchy and control over the population. If indeed you can improve your lot in the next life by living well in this one, why dwell on how miserable your life is now if you can focus on having a better one next time around? It is also interesting that the four paths in life aren’t just about spirituality and God. The second and third goals are really about daily life — specifically, living a pleasurable daily life. In this view, the path toward moksha seems enjoyable. You’re supposed to be happy, wealthy, and successful. This sounds a lot like later seventeenth and eighteenth century political philosophies that would shape the founding of America: life, liberty, and the pursuit of happiness. Focusing on the positive and trying to achieve happiness now does indeed bring meaning to life and lift people’s focus away from daily drudgery or suffering, with the hope that one day people might achieve eternal salvation or be released from the reincarnation cycle (samsara). The second religion I’m going to take a look at is Buddhism. Buddhism evolved from Hinduism and the ancient Indian social structure. In this case, there is a male founder of the religion. His name was Siddhartha Gautama and he was born in South Asia (what is now Nepal) in 563 BCE. He was born into a Ksatriya Hindu family, which was the warrior/ruler class. The story goes that Siddhartha’s father asked some wise men what his son would become in life. These wise men said he would become a great leader, unless he saw suffering. So Siddhartha’s dad kept him inside the palace walls all of his life. When he was 16, he got married and had a son. Then, he went outside of the palace and saw all the illness, poverty, death, and human suffering in the world.He fled his home and began to search for peace. Siddhartha spent six years wandering around South Asia trying to find ways to ease the suffering of the world. One day, he sat under a Bodhi tree to meditate. While he was meditating, he became enlightened, or saw the truth. This is how he earned the name Buddha, the Bhodi Satva, or the Enlightened One. After his enlightenment, he began to share what had been revealed to him under the Bhodi tree. These teachings include the Four Noble Truths and the Eight-Fold Path. I learned that the whole purpose of ending suffering (dukkha) in the world is to achieve the ultimate goal of enlightenment (nirvana). The Four Noble Truths: Life is filled with suffering (dukkha). The root of this suffering comes from a person’s material desires (to want what you do not have). In order to stop suffering, you must get rid of desire or greed. If you follow the Eight-Fold Path then you can eliminate your material desires, and therefore, your suffering. The Eight-Fold Path Right View: Understand that there is suffering in the world and that the Four Noble Truths can break this pattern of suffering. Right Intention: Avoid harmful thoughts, care for others, and think about more than yourself. Right Speech: Speak kindly and avoid lying or gossip. Right Action: Be faithful and do the right thing; do not kill, steal, or lie. Right Living: Make sure that your livelihood does not harm others. Do not promote slavery or the selling of weapons or poisons. Right Effort: Work hard and avoid negative situations. Right Awareness: Exercise control over your mind and increase your wisdom. Right Concentration: Increase your peacefulness and calmness, in particular through meditation. What a story! This young man from the upper class of society gave up his status and position when he saw the effects his status was having on people outside of his palace walls. These eight tenets of Buddhism are really about how people should relate to each other and how people develop self-discipline. Each of the eight “rights” is a simple statement about how to ease suffering in life. They are simple and they are, in fact, present in one form or another in all of the other religions as well: be kind to each other, don’t gossip, don’t kill or steal, be loyal, make good choices, learn a lot, and chill out. I also learned that after he revealed these ideas, the Buddha stopped worshipping Hindu gods and stopped believing that one caste was better than the others. But similar to Hinduism, Buddhists came to believe that following these steps leads toward nirvana and therefore, stops the cycle of reincarnation. So what have I learned about the development of early religions from studying Hindu-ism and Buddhism? In both cases, the development of religious ideology was intimately linked to the already established systems that humans used to relate to one another — the social hierarchy of caste, in this case. The major ideas in each religion provided more structure and guidance for how people should peacefully relate to one another and how they should live their best lives. Both provided a pathway and documents (texts) on how to earn salvation — in this case, by ending the cycle of reincarnation. This short journal entry is an example of how historians go about exploring important questions and looking at new information. They use a mixture of historical documents and the writings of other historians to inform their thinking. All sources are listed in the working bibliography. [Sources and attributions]

Introduction to Agrarian Civilizations A White Marble Head of Buddha. Tang Dynasty © Christie’s Images/CORBIS By Cynthia Stokes Brown During the same narrow sliver of cosmic time, cities, states, and civilizations emerged independently in several places around the world. Definitions The first agrarian civilizations developed at about 3200 BCE in Mesopotamia, in Egypt and Nubia (now northern Sudan), and in the Indus Valley. More appeared in China a bit later and in Central America and along the Andes Mountains of South America at about 2000–1000 BCE. Why and how did this occur? For a meaningful discussion, definitions of the key words city, state, and civilization must be clear. A “city,” with tens of thousands of people, is larger than a town (thousands) or a village (hundreds). But it is also different in nature, with people specializing in some particular aspect of work instead of being farmers and being supported by surplus food grown by farmers nearby. A “state” is a city, or several cities, plus the surrounding villages and farms. A state would include tens to hundreds of thousands of people, even millions. It would have political, social, and economic hierarchies, meaning that a few elite people at the top, maybe about 10 percent, had more wealth and power than the remaining 90 percent. A state was ruled by elites who exercised the right to use force to ensure order and who maintained the right to collect taxes/tribute, by force if necessary. Out of states arose imperial states, or empires, in which a single ruler controlled large territories of cities and farmland. These large states are often called “civilizations.” This word has previously been used to imply superiority or advancement; historians now try to use it simply to mean that civilizations have certain characteristics, primarily density of population and control by elites. This does not mean they are better than other kinds of societies, but they are, by definition, more complex. Since these early civilizations always depended on the farming around them, we call them “agrarian civilizations.” Places of Early Civilizations Four of the earliest agrarian civilizations occurred in fertile river valleys, utilizing plants and animals that had been domesticated earlier as their foundations. ​The first of these formed in Mesopotamia, the land between the Tigris and Euphrates rivers in what is now Iraq. The valleys of these rivers had no large trees, no big stones, and no metals, but with irrigation people could grow large crops of wheat and barley, grasses that had been domesticated earlier in the mountains nearby. They also grew lentils and chickpeas and herded sheep and goats. The next three places where agrarian civilizations emerged were in the Nile River Valley in Egypt and Nubia, the Indus River Valley in India, and the Huang He (Yellow) River Valley in China. Each river valley had its own distinctive plants and animals, which had been domesticated from the neighboring ecosystem. The Egyptians and Nubians had wheat, barley, cattle, fish, and birds. The Indus Valley people raised humped cattle and cotton, as well as wheat, barley, lentils, sheep, goats, and chickens. In China millet and wheat were grown in the north, with rice cultivated later in the south. Pigs, chickens, and soybeans also formed the staple foods in China. Egyptian fresco, c. 1306–1290 BCE © Bojan Brecelj/CORBIS Large states emerged a couple of thousand years later in the Americas, where the food base proved quite different. Wild grasses were not present to be domesticated, and there were only a few large animals. People in Central America domesticated maize (corn), peppers, tomatoes, squash, beans, peanuts, and cotton. They had only dogs and turkeys as domestic animals. Along the Andes Mountains in South America people used llamas and alpacas for wool and transport; for food they depended mostly on potatoes and quinoa, a grain rich in protein. They had guinea pigs, and fish brought up from the coast, where seafood had supported earlier dense coastal populations. Why and How Did States Emerge? After people learned to domesticate plants and animals, they gradually learned to utilize animals for a variety of things. They used milk, wool, manure, and muscle power from animals instead of eating them right away. The increased cultivation and development of available resources caused the world’s population to grow dramatically, from perhaps 6 million in 8000 BCE to maybe 50 million in 3000 BCE. At the same time, the climate was changing dramatically. Stable warmth had been reached by about 8000 BCE after the height of the last ice age, about 20,000 BCE. After 8000 BCE the climate in the northern hemisphere generally became drier, as the monsoon belt shifted southward (possibly due to slight changes in the Earth’s orbit). This dryness drove people from upland areas down into river valleys, where access to water was more certain. The fertility of these valleys, from rich soil deposited during floods, produced abundant food. As density and food surpluses increased, the social structure changed. A small part of the population became much wealthier and more powerful than the rest. Why did the majority of people allow this to happen? We can only guess that people needed leadership to manage projects like large-scale irrigation or distribution of surplus food. They also needed armed protection against neighboring groups. At the same time, ambitious priests and rulers could take opportunities to control the food surpluses to increase their own power. Gradually they were able to institutionalize their power, forming political or religious groups that held significant control over the land and people in their jurisdiction. Areas Without Early Civilizations Even though some areas of the world did not produce full-blown cities and states, the trend toward agriculture seems to have been present everywhere. In sub-Saharan Africa (below the Sahara Desert) people were separated from the northern coast by a harsh desert. Malarial rain forests covered much of the land, with lots of tropical diseases. The Bantu people, in the eastern part of modern Nigeria, cultivated yams, oil palm trees, millet, and sorghum and herded cattle. Eventually camels replaced horses and donkeys for travel across the Sahara, and Muslim merchants could make their way to the west coast. Small regional states and kingdoms emerged, but never a major agrarian civilization. Small islands in the Pacific did not have the resources to create full-scale agrarian civilizations, but their smaller states and chiefdoms had features similar to those around the world. On the larger island of Australia it seems that agriculture never materialized. Soils were poor, and the island was isolated. New evidence suggests that trends toward the development of agriculture might have continued if not broken by the arrival of European colonists. Archaeologists have long thought that resources could not support dense human societies in the basin of the Amazon River. But recent evidence suggests that people there found ways to fertilize the soil by adding charcoal and that the present rain forests may have been earlier orchards supporting large populations. Comparing Early Agrarian Civilizations All of the earliest agrarian civilizations developed many similar characteristics beyond the defining ones of hierarchical force and coerced taxation/ tribute. It seems that only centralized state control can effectively integrate and support large populations of people. Other common characteristics of civilizations include the following: 01 - Storage of surplus food 02 - Development of a priestly caste; a state religion based on supernatural gods/goddesses 03 - Central authority — a ruler (such as a king, pharaoh, or emperor) 04 - Occupational specialization and division of labor 05 - Social stratification (social divisions based on wealth, ancestry, and occupation) 06 - Increased trade 07 - Systems of writing or recording information; increased collective learning 08 - Standing armies; increased warfare 09 - Monumental public architecture 10 - Increased gender inequality; patriarchy Despite all these similarities, some important differences occurred among early civilizations. Perhaps most significant, the civilizations in northern Africa and Eurasia were connected with each other soon after they began, forming an Afro-Eurasian zone that included the trading of goods and the exchange of ideas and technology. Connecting roads went east-west through similar latitudes and there were sea routes between numerous ports. In contrast, early civilizations in the Americas were hardly connected at all. They had fewer kinds of transport animals and fewer routes over difficult terrain that separated the north-south changes in latitude. This difference would prove important when sailors from Europe arrived on the shores of the Americas with horses, guns, steel swords, and germs they had picked up from their domestic animals but had themselves become immune to or tolerant of. The Europeans’ animals and technologies were the result of collective exchanges among several early Afro-Eurasian civilizations. If we change our lens to get close-ups of early civilizations, we can see many fascinating details that differ. All the early civilizations developed some form of writing, except the Inca in the Andes, who instead used a system of tying knots in different colored string, called quipu, to record their transactions and possibly even their stories. All early civilizations engaged in warfare except, perhaps, in the Indus Valley, where some arrowheads and spears have been found but no swords, helmets, shields, or chariots. Every civilization with writing started by using pictographs but switched to some form of alphabet, except the Chinese, who still use pictographs in their writing. Every civilization practiced human sacrifice, but the Aztecs used it on a much larger scale than others; they believed that the world would end if the chief god did not receive his daily offering of human blood to keep the Sun shining. While early civilizations shared many common features, the differing details form a mosaic of human culture. For Further Discussion This article provides criteria for comparing civilizations. What two ways of comparing do you think are most important and why? Share your two comparisons and reasons for choosing those in the Questions Area below. [Sources and attributions]

Agriculture and the Power of Networks Terraces in Rwanda © Tom Martin/JAI/CORBIS By David Christian In the second essay of a four-part series, David Christian explains how the spread of agriculture and the rise of civilizations generated powerful networks of collective learning. Farming Speeds Up the Pace of Collective Learning When agriculture appeared, history seemed to speed up. Five thousand years after the appearance of agriculture, the number of humans had increased almost 10-fold, from just a few million to almost 50 million. This rapid growth was made possible by an increase in the number of innovations. Farmers spread into wooded and semi-arid zones, designed new types of buildings, discovered ways to domesticate animals, pioneered new uses for clay and metals, and began to develop simple forms of irrigation. With the appearance of agrarian civilizations, the rate of innovation increased again. Architects designed monumental architecture like pyramids and temples; metalworkers made refined tools and weapons; writing appeared, providing more reliable ways of storing and preserving information. With the domestication of horses and camels, goods and people were moved over large distances; meanwhile, sailors and merchants figured out how to travel across the Indian Ocean and into the Pacific Ocean. There was also innovation in government and lawmaking, in the types of religion, and in art and literature. New goods, including glassware, jewelry, and the coins that enabled trade and taxation to evolve, were made. Defining Networks Collective learning was accelerating, but to understand how and why, we need to think about how humans exchange ideas. When several individuals are linked, they form a “network.” Networks appear in many different varieties. The Internet is a network of computers; economies are networks of individuals who are buying and selling; proteins within a cell form networks linked by different chemical reactions; the electricity grid is a network. All networks contain two main kinds of things: points, and links between the points. The First Rule About Networks: Size Matters! It may seem obvious that more ideas can be exchanged if there are more people. But as ideas are shared they often change in subtle ways as different people contribute their own ideas. So the act of sharing can add new information. In addition, the sheer number of possible exchanges increases very quickly as the number of people rises. How many possible links are there between three friends? The answer is three. Between four friends? The answer is not four; it is six. You can see this by drawing lines between four points. How many links are there between five friends? The answer is 10. We can calculate the relationship between nodes and edges precisely using a mathematical formula but the main trend is that, as groups get larger, the number of possible links within the network increases much faster than does the number of people. So in large groups, the possibilities for sharing information are much greater than in small groups. This tells us something powerful about the impact of agriculture. Remember that in the Paleolithic era, most communities were tiny, usually with fewer than 40 or 50 people. Much larger communities — villages with, say, 2,000 inhabitants — developed with the appearance of agriculture. A village this size would produce a network of 2 million possible links. Of course, not everybody would link up with everyone else, but the possibilities were there. Once you had towns with, say, 10,000 people, almost 50 million links between individuals were possible. With the rise of agriculture, collective learning seems to have accelerated, generating more ideas much faster than ever before. Diversity Is As Important As Size Networks, The Big History Project The diversity of people and information in a network is as important as a network’s size. If everyone lives and thinks exactly like everyone else, there won’t be much new information to exchange. But in reality every individual has something new to contribute. In our network model (opposite), we can imagine that the blue area represents people living near the coast, while the other shades represent people living in fertile woodlands and in arid desert lands. Each community would have slightly different ways of providing food and shelter, slightly different forms of clothing, different rituals, and different stories. An anthropologist might say that each group has a slightly different “culture,” just as today your family may have different rules about eating or studying or cleaning up than your friends’ families have. Now imagine an individual moving from a coastal group to a desert group. Perhaps a man from the desert visits his cousins on the coast, marries one of the women living there, and the new couple travels back to the desert. He, from his brief visit to the coast, may have learned a bit about fishing, and she will certainly have to learn how to live in the desert. Both will know more about the world as a whole. Most collective learning probably happens in small, almost invisible stages. In fact, it’s a bit like natural selection, with the appearance of tiny variations in knowledge, some of which will prove interesting or valuable or inspiring enough to catch people’s attention and spread more widely within a network. In other words, we expect to find more innovation and more new ideas in networks in which people live and work and pray and think in different ways. Agrarian civilizations were much larger and more diverse than the societies that preceded them. This was particularly true at their borders, where merchants, soldiers, and officials met foragers, independent villagers, and horse herders. There was also great internal variety. With more productive farming methods, farmers could produce enough food and raw materials to support small groups of non-farmers: kings and queens, scribes and soldiers, poets and priests, potters and weavers. Historians describe this process as the emergence of a division of labor, but it was also a division of knowledge. Different types of specialists acquired different skills and different types of information. Merchants, for example, had to learn about costs and prices in foreign countries; soldiers had to learn about weaponry and tactics; priests had to learn about religious traditions and rituals. The total amount of available information increased rapidly with the development of a division of labor. So networks of collective learning were both larger and more varied in agrarian civilizations. No wonder these societies seemed to generate more technological, artistic, religious, social, and political innovation, as well as more power and more wealth! The study of networks can also help us understand two important features of agrarian civilizations: how they encourage flows of information and how information flows support an uneven distribution of wealth and power. As networks get larger, the amount of connectedness of any single node compared with another node gets more and more uneven. You can see this in our diagrams and in real-life situations. Google, for example, is very well connected because it links to more or less anyone who does a search; meanwhile, your school network is connected mainly to those who work or study at your school. We can see the same quality in agrarian civilizations: isolated villages had limited connections; townships with markets or temples were much better connected; and capital cities were connected to the entire kingdom. The uneven distribution of information and connectedness can help us understand why wealth and power are distributed so unevenly in agrarian civilizations. An individual connected to 10 other individuals can form alliances or teams with those individuals. But an individual connected to 1,000 other individuals has access to more information and can form greater and more powerful alliances. (This is perhaps why we say of powerful people that they are “well connected.”) More connectedness seems to mean not only more information but also more wealth and power. Specifically, in all agrarian civilizations we find elite groups that are wealthier and more powerful than most of the population. If you were to map information exchanges in society, you would find that the wealthy and powerful are also information hubs; to a great extent, they maintain control of the storage and dissemination of information. If you are a king, you have scribes and priests and spies who can store large amounts of information for you and carry out your orders. You also have long-distance links with a whole class of nobles and officials and merchants, who in turn are connected to the farmers who provide most of society’s wealth. If you are a peasant living in a remote village, your connections will be fewer and less diverse. How Collective Learning Works Rule 1 - Collective learning increases when more people are connected Rule 2 - Collective learning increases when there is greater diversity within a network Rule 3 - Uneven distributions of information produce uneven distributions of power and wealth Positive feedback cycles compound the effects of these three rules, accelerating collective learning' For Further Discussion Do you agree with the idea that when there are an uneven number of connections among people, groups, or countries that this unevenness can lead to differences in the way power, wealth, and influence are distributed? Post your ideas in the Questions Area below. [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. First read: skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Second read: understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: What happened Ibn Khaldun's political career? How did this affect his work as a scholar?What is 'Al Muqaddimah'? Why was it important?What does Ibn Khaldun say is a key element in society's functioning?How did Ibn Khaldun approach important figures like Timur?Looking at just the images and colors in this graphic biography, what ideas do you think the author could be conveying about societies during this time? Third read: evaluating and corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: How did the work of Ibn Khaldun influence what was known about the rise and fall of societies? How might this have contributed to the increasing complexity of civilizations? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. Ibn Khaldun - Graphic Biography Writer: Eman M. Elshaikh Artist: Argha Manna Ibn Khaldun was a North African Arab scholar and politician who pioneered the social sciences. Download the Graphic Biography PDF here or click on the image above.

The Ghana Empire By David Baker West Africa independently developed agriculture, and the “human experiment” proceeded for many centuries as West Africa developed large and complex states, before getting caught up in the “unification of the world zones.” The start of West African states West Africa was one of those regions of the world that, like the Fertile Crescent, independently invented agriculture. Around 3000 BCE, West Africans had begun the “energy bonanza” that supports many more people in a given land area than foraging. Al-though the rest of sub-Saharan Africa did not begin adopting agriculture until 1000 BCE or later, West Africa began the process around the same time as the Americas. It launched into the development of agrarian civilizations around the same time as well. This contradicts the myth that Africa was always “disadvantaged” or “primitive” in comparison to some other world zones. For centuries, West Africa independently blazed the trail of rising complexity in human culture, before it was swept up in the unification of the world zones and the clashes and tragedies that resulted. Complex societies emerged in West Africa around 1500 BCE, and the archaeology of the region reveals a number of settlements. By 600 BCE, there were some large towns and villages in West Africa where there was enough of an agricultural surplus that not everybody needed to farm, but could perform the duties of rulers, artisans, engineers, and bureaucrats. By this time, many cultures were also making thorough use of iron technology, which further increased farming productivity. One of the earliest complex societies of this time was the Nok culture in northern Nigeria. Their terracotta statues portray people in a variety of societal roles and indicate an immense amount of hierarchy, division of labor, and cultural complexity. Further to the west, there were many farmers on the Sahel, a strip of land running across Africa just below the Sahara. Around 1000 BCE, the climate of the Sahel was wetter than it is today and there was a lot of grass for pasture. The inhabitants of the western Sahel herded cattle and farmed millet and sorghum. By 1 CE, there were many large urban centers. Dhar Tichitt was one such place, and formed a hub for the many herders and farmers of the region. However, as the climate got hotter, the town was abandoned and the inhabitants migrated farther south in the Sahel, where the grasses still grew in abundance. This more southerly region was to become the power center of West Africa’s first major empire: Ghana. One thing to note is the Ghana Empire was not where the modern country is today. Instead, the modern country was named in honor of this powerful, ancient, and independent West African civilization. You will notice that the dates for rising agrarian states in West Africa “lag behind” those of the Mediterranean and the Middle East. At the beginning of the Common Era, West Africa had formed large urban centers and small kingdoms. But to the north and east, the Romans had already established a sprawling empire, as had the Greeks and Egyptians before them. The same goes for the mighty Persian Empire in the Middle East and the Akkadians, Assyrians, and Sumerians before them. The earliest states in the world arose around 3500 BCE, in Mesopotamia, just as agriculture was getting its independent start in West Africa. Farming in the Fertile Crescent, meanwhile, had be-gun to appear approximately 10,000-8000 BCE. The Fertile Crescent and its descendant powers thus had a head start on West Africa by many thousands of years. Yet within just 3,000 years, West Africa had developed complex agrarian states of its own. The Ghana empire While there were many city-states and small kingdoms in West Africa for centuries, the Ghana Empire was the first major agrarian empire to arise in the region. Its history is shrouded in mystery. While they had a complex society, a division of labor, wealth, and trade, the Ghana Empire (like the Inca in the Americas) did not have a form of writing as we know it. As such, much of the information we have of the civilization depends on oral histories and the medieval writings of Arab traders. The story goes that a man named Kaya Magar Cissé, king of a realm called Wagadou, rose to prominence in West Africa around 300 CE. The sons and grandsons of his house then extended their rule over several other kingdoms, turning them into vassal states. Many of the names of the Ghana rulers are unknown and only a few of their deeds have passed into recorded history. Range of the Ghana Empire in West Africa What we do know is, around 300 CE, West Africans domesticated the camel. That species has a dis-tinct advantage in the desert, and this revolutionized trade across the Sahara. Rapidly growing trade brought a lot of wealth and power to West Africa, just as the Ghana Empire was getting its start. The Ghana Empire, in particular, grew rich from the trans-Sahara trade. It certainly helped that the empire had control over the three major gold fields to the south of them. As such, Ghana was referred to by traders as “the Land of Gold,” and the kings of Ghana were sometimes called “the Lords of the Gold.” As a result, the empire flourished. The king of Ghana had a monopoly on all gold nuggets that were found in the mines. The people were allowed to trade in gold dust, but had to turn over any gold nuggets to the government. As such, the state became very powerful as well, adding to the complexity of Ghana’s agrarian civilization. Once the Arabs moved into Egypt and Northwest Africa in the 600s and 700s CE, trade intensified and Ghana grew even richer. The West Africans became major traders in the Old World. They sold ivory, salt, iron tools and weapons, furniture, textiles, sandals, herbs, spices, fish, rice, honey, and kola nuts. This is also the point in history when the large exportation of slave labor from West Africa to the Islamic world began. Centuries later, with the arrival of the Portuguese, a similar exportation of African people as slave labor would kick off the massive coerced exodus of Africans to the Americas, in which millions died in the appalling conditions of the crossing, and mil-lions more led a life of subjugation and cruelty once they arrived. Slavery is a negative characteristic of many early agrarian civilizations, from Mesopotamia, to Egypt, to the Greco-Romans, but in the long run it was to prove particularly devastating to the populations of West Africa, after about 1500 CE. It was the monopoly on West African gold, however, that allowed the Ghana Empire to reach the height of its power, at a time when Europe was undergoing decline after the fall of the Roman Empire. Ghana’s rule extended as far as the Niger valley. The city of Koumbi Saleh, thought by many archaeologists to be the empire’s capital, is estimated to have supported 15,000 to 20,000 people. This may not seem like much compared to other ancient cities. However, this was an astounding feat for a city in the Sahel, where the climate was dry and drinking water was scarce. The town had many wells to support its populace, and also to irrigate plants that were grown within the city. The fact that 15,000 to 20,000 people were able to live in a city so close to the harsh Sahara is an astounding feat of architecture and engineering. Koumbi Saleh also boasted an impressive palace complex with a number of ornate buildings to house the many nobles, officials, and the king. The ruler of the Ghana Empire is also said to have sent many opulent gifts to his neighbors. This was easily done, considering the immense amounts of gold he possessed. Also, Arab sources tell us that in the 1000s, the Ghana Empire could field 200,000 soldiers in the field, of whom 40,000 were archers. The number is almost certainly exaggerated, as medieval writers are known to do, but the point is that the empire’s military force was considerable and enough to give Arab visitors cause for amazement. All seems to indicate that thanks to agriculture, mining, and trade, Ghana was a wealthy and powerful civilization in Africa. Its society was to dominate the region for centuries. It was West Africa’s first major power, and was not the last. Competition of agrarian states The competition between agrarian states is a universal characteristic of this stage of human complexity. Once the process of agrarian civilization begins, and humans start to get better and better at harnessing the food and resources (or put more simply, energy) of their environment, different civilizations begin competing for that energy. In that sense, they are similar to organisms competing for access to energy in nature. All of them seek energy to either sustain or increase their complexity. In the eleventh century, Ghana’s power was first challenged by the Almoravids, a powerful force that arose in the Atlas region and became masters of the Western Sahara. We know that there was conflict of some kind between Ghana and the Almoravids, perhaps even with the capital, Koumbi Saleh, being sacked, as Arab sources claim, though the archaeological evidence makes this seem doubtful. At any rate, the Ghana Empire managed to fend off the Almoravids, who in the next century went into decline. Range of the Almoravids, in Northern Africa In the twelfth century, Ghana began incorporating more Muslims into its government, including the master of the treasury, diplomats, and, some sources say, even the majority of officials. By then end of the 1100s, Ghana had converted entirely to Islam. Previously, Ghana had subscribed to an animist religion, which involved spirits of the forests and sacred groves that only priests could enter. By 1200, however, Ghana was becoming more and more culturally incorporated into the Afro-Eurasian world zone as trade continued to share collective learning. West Africa sat at the very end of a long network forming the Silk Roads that stretched across the Afro-Eurasian supercontinent. Ghana’s long period as the dominant agrarian civilization of West Africa came to an end in the 1200s. Scholars have argued that climate change played a role. The wet climate that had once made farming prosperous in the Sahel continued to deteriorate. With dwindling resources and power, along with some political infighting, Ghana left a power vacuum that was soon filled. Rivals called the Sosso briefly occupied territories of Ghana, including its capital, and built their own short-lived empire. They, in turn, were conquered by the Mali Empire, who forged an even larger and wealthier empire in West Africa. They, in turn, were overthrown by the Songhai Empire in the 1400s. In the 1590s, however, the Songhai Empire fell to the Moroccans who overpowered them with the use of early muskets, which were the product of collective learning imported from elsewhere in the world. From that point forward, West Africa got increasingly caught up in the global story, as the world zones became increasingly unified The West African "experiment" West Africa became characterized by smaller kingdoms. Powerful Islamic states exerted an increasing amount of influence from the north. Then, the European slave trade began. The Europeans took West African slaves in their millions to the Americas. This had a disastrous effect on the population numbers and collective learning of West Africa, removing thousands upon thousands of potential innovators to lives of bondage and manual labor overseas. Along with commoners, West African agricultural experts, engineers, soldiers, and bureaucrats found themselves suddenly ripped from their po-sitions and their homes. The sheer scale of the slave trade did severe damage to West African societal structures and collective learning. The lucrative nature of the slave trade also did much to turn one West African group against another. For a time, tropical diseases kept European colonialism from gaining too much of a foothold, but by the nineteenth century, West Africa began to fall increasingly under direct colonial rule. All of this is a symptom of the painful transformations that struck many world zones, as they became increasingly unified after about 1500. West Africa and the Americas, for instance, both started to develop agriculture at roughly the same time; they began to build agrarian civilizations at roughly the same time. And while the agrarian civiliza-tions of the Americas were being devastated by European diseases and culturally dev-astated by the encroachments of the Spanish and Portuguese, around the same time West Africa was beginning to suffer the tragedies of world unification as well. The unification of the world zones ultimately brings people together into a close-knit web of collective learning, which can potentially be used to the benefit of all. However, the early phases of global unification were often full of suffering. World zones that en-joyed a head start on collective learning and a great deal of global connectivity had not yet shed the uglier aspects of agrarian civilizations: slavery, religious and ethnic intol-erance, and an all-consuming drive to control more resources. This often had trau-matic and predatory effects on other agrarian civilizations that were smaller or still developing. As Big History teaches us, collective learning can bring us greater con-nectivity and technological advancement, but it is not always fast enough to bring us the wisdom to handle it. While West Africa’s story gets increasingly swept up in the global one after 1500 CE, its agrarian civilizations were an important milestone in the tale of rising complexity. Between 3000 BCE and 1500 CE, West Africa represents another version of the “human experiment” that independently appeared all over the world. If you compare the early world zones to separate “petri dishes,” you can observe the differences and similarities that each “experiment” reveals. In a very short time after the dawn of agriculture around 3000 BCE, West Africa quickly developed large agrarian states, very similar in many respects to the complex agrarian civilizations we see elsewhere in the world. Figuring out what those similarities are is essential to figuring out the core characteristics of all agrarian civilizations. [Sources and attributions]

Repeated Reinventions Sculpted stone Olmec head© Werner Forman/Corbis By Cynthia Stokes Brown Civilization in Mesoamerica flourished and crashed repeatedly, giving rise to a distinctive worldview and some remaining mysteries. The Geography of the Americas The Americas constitute one of the world’s four geographical zones. Each of these belts is a large area of the world that developed almost entirely separately from the others during the eras of hunting and gathering and of early agriculture. The four world zones are the Afro-Eurasian zone, the Americas, the Australasian zone, and the Pacific. About 245 million years ago, when all the continents on Earth were fused into one continent called Pangaea, North and South America were more closely packed together. The current shape of Mesoamerica (Middle America) began to emerge as Pangaea broke up, and North and South America separated, not to be rejoined again until about 3 million years ago. This reconnection happened as two tectonic plates moved against each other, causing volcanoes to erupt, which created islands. Sediment gradually filled in among the islands. This had an enormous impact on Earth’s climate, because it reconfigured the ocean currents. Since the Atlantic current could no longer flow into the Pacific Ocean, it turned north up the coast of North America and over to Europe, carrying warm water from the Caribbean that raised temperatures in Europe. Today the land joining the two continents, called the Isthmus of Panama, is only 40 miles wide and 400 miles long. (Isthmus comes from the Greek word isthmos and means a narrow strip of land connecting two larger land areas, with water on either side.) The areas in which civilization developed in Mesoamerica include Mexico and neighboring parts of Central America, all just north of the Isthmus of Panama. Early Developments in Mesoamerica Detail from The Great Tenochtitlan, a mural by Diego Rivera© Charles & Josette Lenars/CORBIS People in the Americas developed an entirely different menu of foods than those in Mesopotamia for the simple reason that the indigenous plants and animals were different than those in the Fertile Crescent. Instead of wild grains, goats, and sheep, people in the highlands of Mexico had corn (sometimes called maize), beans, peppers, tomatoes, and squash as their staple foods. The ancestor of modern corn, called “teosinte,” has cobs about the size of a human thumb. It took people about 5,000 years, until 2000 BCE, to domesticate teosinte and breed corncobs large enough to support city life. They also cultivated peanuts and cotton. The only animals that could be domesticated were dogs and turkeys. Teosinte: corn’s ancestor, Photograph by Joseph Tychonievich/Greensparrow Gardens The founding culture of Mesoamerica appeared along the southwestern curve of the Gulf of Mexico, near the present city of Veracruz. This culture emerged in a series of river valleys, as Uruk did in Mesopotamia. Called the Olmecs (the “rubber people”), this culture lasted from about 1400 BCE to 100 BCE. It produced nearly imperishable art, notably large carved heads of volcanic rock, the largest weighing some 20 tons and standing about 10 feet tall. Monumental sculptures or tombs are typically indicative of a civilization with powerful leaders, but this culture probably ranks more as a chiefdom than as a state with extensive coercive power. The last Olmec site, Tres Zapotes, declined by about 100 BCE for unknown reasons. Was it volcanic eruptions? A shift in the flow of rivers? Scholars believe that the Olmecs may have deliberately destroyed their capital. Was there civil unrest? Class strife? No one knows. As the Olmecs declined, their neighbors to the east — the Maya — prospered in an area the size of Colorado or Great Britain. This area, around the curve of the Gulf of Mexico on the Yucatán Peninsula and south into present-day Guatemala, had poor, infertile soil and no large rivers, not what one would expect for a flourishing civilization. Yet its people built terraces to trap silt from the small rivers and grew corn, beans, squash, peppers, cassava (manioc root), and cacao (chocolate). With no beasts of burden, their luxury goods were portable by humans — feathers, jade, gold, and shells. The Maya organized themselves into small city-states instead of one big empire. The largest was Tikal, which by 750 CE had about 40,000 inhabitants, in specialized occupations and ruled by elites. The city-states fought each other frequently with the main purpose being to capture their enemies in order to sacrifice them to the Mayan gods. We know about the Maya because they developed the most elaborate and sophisticated writing system of the several different ones used in Mesoamerica. Mayan writing included both pictographs and symbols for syllables. Since the 1980s scholars have made great strides in deciphering this script. Many carved inscriptions have survived, but only a few accordion books on bark or deerskin remain. Relief depicting Mayan king Bird-Jaguar © Jack Hollingsworth/CORBIS Maya shaman/priests worked out remarkable systems of cosmology and mathematics. They devised three kinds of calendars. A calendar of the solar year of 365 days governed the agricultural cycle and a calendar of the ritual year of 260 days dictated daily affairs; these two calendars coincided every 52 years. A third calendar, called the Long Count calendar, extended back to the date August 13, 3114 BCE (on the Gregorian calendar), to record the large-scale passage of time. The Maya calculated a solar year as 365.242 days, about 17 seconds shorter than the figures of modern astronomers. They also introduced the concept of zero; the first evidence of zero as a number dates from 357 BCE, but it may go back further, to Olmec times. In Afro-Eurasia, Hindu scholars first represented zero in the 800s CE. Mayan cosmology included the idea that the world had come to an end four times already and that the Maya were living in the Fifth Sun (the fifth world), whose persistence depended on the life energy of sacrificial blood. Remember in the Mayan creation story, the Popol Vuh, that the gods created people out of their own genius and sacrifice, nothing else. The Maya believed that the gods set the Sun burning by sacrificing themselves to start it. Since they believed that the Sun’s energy would continue only with the life-giving energy found in human blood to replenish it, they practiced ritual bloodletting achieved by using cactus or bone spines to pierce their earlobes, hands, or penises. They also carried out some ritual sacrifice of human victims. The Maya may have inherited their calendar and sacrificial rituals from the Olmecs. Certainly the Maya inherited from the Olmecs a ball game played with a rubber ball about eight inches (20 centimeters) in diameter. The object was to put the ball through a high ring without using hands (no-handed basketball!). Sometimes the game was played for simple sport, but sometimes high-ranking captives were forced to play for their lives. The losers were sacrificed to the gods, and their heads were displayed on racks alongside some ball courts. Between 800 and 925 CE Mayan society experienced a rapid transition. The world of cities ended as populations moved back into the countryside. Historians debate the possible causes of the change — civil revolts, invasions, erosion, earthquakes, disease, drought. Likely some combination of these brought on an unusually rapid fading of a once-vibrant civilization. The Maya didn’t just disappear; several million descendants are still alive today. Meanwhile, back in the center of Mexico at about the same time, another amazing city developed: Teotihuacán (tay-oh-tee-wa-KAHN). Its site was in the highlands of Mexico, more than a mile (some two kilometers) above sea level, in a place where water flowing from surrounding mountains created several large lakes. Teotihuacán began as an agricultural village located about 31 miles (50 kilometers) north of present-day Mexico City, but by the beginning of the Common Era it had grown to some 50,000 inhabitants. By 500 CE it had an estimated 100,000–200,000 people, to rank as one of the six largest cities in the world. Not much is understood about its government; its art portrays deities rather than royalty. Its people expanded Olmec graphic symbols, but all its books were destroyed about 750 CE, when it seems that unknown invaders burned the city and reduced its population to a quarter of its former numbers. Tenochtitlan The Market of Tlatelolco from The Great Tenochtitlan by Diego Rivera© The Gallery Collection/CORBIS The city that carried Mesoamerican civilization to its height proved to be Tenochtitlan (the-noch-tee-TLAHN), or “place of the cactus fruit” in their language, Nahuatl. Its people, called the Mexica (me-SHI-ka), came from northern Mexico looking for a place to settle. All the desirable places were already inhabited, except an island on the shore of a large lake in the Valley of Mexico, where they settled in 1325. They were given the name Aztecs by the German explorer and naturalist Alexander von Humboldt in the early 19th century. The Mexica/Aztecs built up their food production by creating floating islands of soil, called chinampas, held together by willow trees. Their men hired themselves out as paid soldiers to other towns until they became strong enough to conquer others on their own. In 1428 they allied themselves with two other neighboring cities to form the so-called Triple Alliance and set out to conquer other cities to provide tribute that could support the Alliance’s expanding population. The conquests would also provide sacrificial victims for their religious rituals, carried down from the Olmecs, Mayans, and Teotihuacánians. By the early 1500s the Aztecs had conquered most of Mesoamerica and had imposed their rule on an estimated 11–12 million people. The annual tribute they received in corn alone amounted to 7,000 tons. They also received 2 million cotton cloaks, as well as jewelry, obsidian knives, rubber balls, jaguar skins, parrot feathers, jade, emeralds, seashells, vanilla beans, and chocolate. Without money, everyone was paid in food and goods. Their population had grown to at least 200,000–300,000 in the capital, several times the size of the contemporary London of King Henry VIII. The Aztecs bestowed great honor to their warriors, building their society around a military elite. A council of the most successful warriors chose the ruler. Warriors could wear fine cotton cloth and feathers instead of clothing made from the fibers of an agave-like plant; they were believed to go straight to the paradise of the Sun God if they died in battle. (This also applied to women who died in childbirth with their first child.) Priests also ranked among the elite. Most people were commoners who cultivated land and a large number of slaves worked mostly as domestic servants. The Aztecs adopted traditions that dated back to the Olmecs. They played the same ball game and kept a sophisticated calendar. They adopted traditional religious beliefs, holding that the gods had set the world in motion by their individual acts of sacrifice. Priests practiced bloodletting on themselves and believed that ritual sacrifice of humans was essential to prevent the destruction of the Fifth Sun by earthquakes or famine. The god of war, Huitzilopochli (we-tsee-loh-POCK-tlee), came to be the prevailing god in Tenochtitlan, and his priests placed more emphasis on human sacrifice than did earlier traditions. Priests laid the victims — mostly captives of war — over a curved stone high on a pyramid and cut open the chest with an obsidian blade to fling the still-beating heart into a ceremonial basin, while the desired blood flowed down the pyramid. Aztec society provided universal schooling for both boys and girls between 15 and 20 years of age. It’s likely they were the only people in the world to do this in the early 16th century. Commoner boys learned to be warriors; girls learned songs, dances, and household skills. A third kind of school provided lessons in administration, ideology, and literacy for elite boys. At the same time that the elites supported warfare, they also devoted themselves to poetry, which they considered the highest art. One of the rulers of another city in the Triple Alliance, Nezahualcoyotl (“Hungry Coyote”), composed this poem in the early 1400s, revealing the Aztec sense of the fleeting world: Truly do we live on earth?Not forever on earth; only a little while here.Be it jade, it shatters.Be it gold, it breaks.Be it quetzal feathers, it tears apart.Not forever on earth; only a little while here.Like a painting, we will be erased.Like a flower, we will dry up here on earth,Like plumed vestments of the precious bird,That precious bird with an agile neck,We will come to an end.(Leon-Portilla, 1992) Truly do we live on earth?Not forever on earth; only a little while here.Be it jade, it shatters.Be it gold, it breaks.Be it quetzal feathers, it tears apart.Not forever on earth; only a little while here.Like a painting, we will be erased.Like a flower, we will dry up here on earth,Like plumed vestments of the precious bird,That precious bird with an agile neck,We will come to an end. (Leon-Portilla, 1992) In 1520, just as the Aztec civilization of the Fifth Sun was flourishing, it was destroyed — by a small group of Spanish conquistadors and their Mexican allies, under the command of Hernán Cortés. After many battles in which the Spanish used their horses, guns, and steel swords to their advantage, they surrounded Tenochtitlan and starved its inhabitants; many Aztecs died of smallpox, to which they had no immunity since it was a disease that originated in cows. When the Aztecs surrendered, only one-fifth of their initial population remained. Within 10 years the Spanish controlled all of Mexico, easily overwhelming the traumatized survivors of the overwhelming disease. How do we know this? The Aztecs had a system of writing, although it was not as expressive as that of the Maya. The Spanish conquerors destroyed the books of the Aztecs, in an attempt to eradicate their religious beliefs; only a few books, and many inscriptions, remain. But a Franciscan priest, Bernadino de Sahagun (1499–1590), learned the Aztec language, Nahuatl, and interviewed many Aztec survivors to produce a 12-volume encyclopedia of their customs and beliefs. Nahuatl is still a living language for hundreds of thousands of Mexicans. It has given English such important words as chocolate, tomato, coyote, and tamale. Comparing Tenochtitlan to Uruk, we can say that there are remarkable similarities. Both cities had social and occupational hierarchies with elite rulers, some slaves, lots of warfare, coerced tribute, monumental buildings, powerful religious rituals, and fantastic art and literature. The differences are also striking: Tenochtitlan’s emphasis on human sacrifice, its anxiety about the world coming to an end, and its emergence thousands of years later than that of Uruk. Comparing the Americas to Afro-Eurasia To compare the Americas with Afro-Eurasia, let’s look around the Americas a bit. We have seen agrarian civilization develop in Mesoamerica; can we find it anywhere else? In South America, civilization developed along the lengthy coastline on the western side of the continent. Plate tectonics formed a unique landscape with high mountains near the ocean as the Nazca plate slid beneath the South American plate. Early states developed along the coastline, but they could not overcome the frequent floods, earthquakes, and torrential rains to continue their development and grow their populations. Finally, in the 15th century, the Incas built a state high in the mountains with its capital at Cuzco, at 13,000 feet. At its height the Inca Empire controlled 10–11 million people, covering lands from present-day Quito, Ecuador, all the way to Santiago, Chile. Strikingly, this civilization had no written language; it used knots tied into ropes as a system of writing called quipu. But smallpox spread to this area even before the Spanish soldiers arrived, and by 1527 the Spanish conquistadors under Francisco Pizzaro had used their technological advantage to conquer a vast Inca civilization compromised by disease. Mesoamerica Timeline. Click here for a larger version. Download PDF. Nowhere else in the Americas did civilization, as we have defined it, emerge. Many wonderful cultures and chiefdoms arose, but none achieved the surplus of food necessary for highly dense populations. The cultivation of tobacco and corn spread widely. Even the basin of the Amazon River may have been more densely populated than previously suspected. People farmed, but everywhere they needed to supplement their agriculture with hunting and gathering. The Americas did not develop many of the technological innovations present in Afro-Eurasia. For example, Americans did not use wheels (except the Maya, who put them on toys!), probably because they had no large domestic animals to pull wheeled devices. Americans did not melt iron or steel; they used obsidian (glassy volcanic rock that can be sharpened to a thinness of one molecule) for blades. They had no swords or guns. They had no horses, which had evolved in the Americas but which had gone extinct at the end of the last ice age, about when humans were arriving in the Americas. How much long-distance trade and travel occurred in the Americas? Not as much as in Afro-Eurasia, which stretched out east to west so that people could travel at approximately the same latitude (the distance from the equator) in similar climates. The Americas stretched north and south, with huge changes in climate. Crops could not be carried or exchanged because they would not grow at different latitudes without time to adapt. Americans built large canoes but not sailing vessels, and they stayed close to the shore and in calm waters. They made north-south connections, but these were less frequent than the east-west connections of Afro-Eurasia. As a result of these factors, states and civilizations arose somewhat later in the Americas than they did in Afro-Eurasia. Once American civilizations emerged, they were not able to connect with each other, share their innovations, or learn collectively to the same extent as their counterparts in Afro-Eurasia. The civilizations created were similar in all their basic characteristics to those in Afro-Eurasia and seemed likely to continue their development if they had not been prematurely cut down by Europeans. Most historians believe that the difference in disease immunity made the biggest impact when the people of the two hemispheres connected in 1492. Many common diseases in Afro-Eurasia — measles, smallpox, influenza, diphtheria, and bubonic plague — had originated in domestic animals and then passed to humans, who are closely enough related that some of the same bacteria and viruses are harmful. Since Afro-Eurasians had frequent contact with domestic animals, they developed some immunity to the diseases by being exposed to mild forms of the dangerous microorganisms as children. Disease exchanges along the Silk Roads spread these immunities. This could not happen in the Americas without domestic animals; when Africans and Europeans brought these “bugs” to the Americas, plus malaria and yellow fever from tropical Africa, wholesale disease and death overtook the Americans. Historical and geographical contingencies gave Europeans the edge in conquering the people of the Americas, while many Africans were swept into prevailing events as valuable slave commodities. It is a disturbing story, but it is the one that helped create the modern world. For Further Discussion In the Questions Area below, provide your answer to the following question: Do you think the north-south orientation of the Americas, as opposed to the east-west orientation of Afro-Eurasia, is a convincing explanation for the differences between the two world zones? [Sources and attributions]

Early Experiments in Participatory Government A Roman statue of Athena© Mimmo Jodice/CORBIS By Cynthia Stokes Brown Instead of rule by a single person, Athens and Rome developed governments with widespread participation by male elites, which lasted about 170 years in Athens and about 480 years in Rome. Deep Time Present-day Greece, with Athens as its capital, and Italy, with Rome as its capital, are neighbors along the northern shore of the Mediterranean Sea. Eighty-five million years ago they were already neighbors, but across the sea on a thumb of land, a promontory of the continent of Africa. By 55 million years ago continental drift had carried the European and African continents together, and by 5 million years ago the promontory consisting of the future Italy and Greece had collided with the European crust, overriding it and piling the deformed crust higher and higher, creating the Alps and the mountains of Greece. After 5 million years of rocks and water pouring out of the Alps over Italy, countless earthquakes, the apparent drying out and refilling of the Mediterranean Sea, and microplates (Corsica and Sardinia) swinging down the Italian peninsula, the northern coast of the Mediterranean became the setting for the development of two distinctive societies, with the Romans eventually swallowing the Greeks as part of the Roman Empire. Location and Food On the Greek peninsula the Greeks occupied the southern shoreline, called Attica. Another group, the Macedonians, inhabited the northern territories. Attica was composed of rocky soil on steep mountains. The poor soil could sustain barley, grapes, and olive trees, and could accommodate sheep and goats, but not much else — just some figs and lentils. Hence, Greeks stayed near the coast and took to the sea for extra food and for trading with other people. Fortunately for Athenians (who had built their city near the southern coast of Attica), a large silver deposit near Athens brought them wealth and paid for additional timber from Italy, which they used to build warships that gave them a powerful navy. (Athenians reduced their own forest cover from about 50 percent in 600 BCE to about 10 percent in 200 BCE.) The Temple of Minerva, Athens, Greece© Fine Art Photographic Library/CORBIS The Romans had a more productive site on the western side of the Italian peninsula. They built their city on seven hills by the Tiber River, not at the seashore, but inland 18 miles (30 kilometers). This gave them protection from naval attacks, while they could still access the Mediterranean by river to the port city of Ostia. To the north lived the Etruscans, and to the south Greeks formed colonies along the coast and on the island of Sicily. In their fertile river valley, early Romans grew wheat, barley, oats and rye, grapes, and olives. They used goat’s and sheep’s milk for cheese. Their local fruit trees included apples, pears, plums, and quince. They harvested many vegetables, but not corn, potatoes, or tomatoes — those came later from the Americas. For meat, they had fish, oysters, chickens, ducks, geese, and pigs; they seldom consumed cows. Salt, found in selected places, was controlled by the government. Soldiers were sometimes paid in salt, a practice from which our word salary derives, as does the phrase “worth your salt.” Athens and Greece From 1600 to 1100 BCE Indo-European immigrants, called the Mycenaeans, occupied the mainland of the Greek peninsula. They attacked Troy, a city in Anatolia (now Turkey), on the other side of the Aegean Sea from Greece. This war is described in The Iliad, one of the earliest written pieces of Western literature, attributed to Homer and written down around the eighth century BCE. By 800 BCE small, competing city-states, called “poleis” (or singular, polis), were forming in the mountains of southern Greece. These city-states each contained some 500–5,000 male citizens and had varying degrees of popular participation in political life. The total Greek population may have been 2–3 million. The city-states shared a common language and religion, and after 776 BCE they came together every four years for competitive games held near Mount Olympus. A Greek silver coin from about 160 BCE© Hoberman Collection/Corbis The Greeks used their expanding population to set up more than 400 colonies along the shores of the Mediterranean and the Black seas between the mid-eighth and late sixth centuries. Their colonies in the Black Sea gave them access to fish, furs, timber, honey, gold, amber, and slaves from southern Russia. Greece introduced metallic coins in the seventh century BCE to facilitate trade; by 520 BCE they carried Athens’ emblem of an owl, the sacred bird of the goddess Athena. Instead of expansion by conquest, the early Greeks expanded by colonization. Sparta and Athens, the chief city-states, differed profoundly in their culture and politics. The Spartans conquered their neighbors and forced them to live as slaves, providing agricultural labor. To keep them in control, Sparta developed an austere culture based on maintaining an elite military force, with a ruling council of 28 elders. Athens, on the other hand, gave wealthy men full political rights. A growing number were added as they could afford armor and weapons to serve in the army (a duty of all participants in government). By 450 BCE holders of public office were chosen by lot, and even the 10 military generals were elected. Since women, children, slaves, and foreigners had no vote, perhaps 10–12 percent of the estimated 300,000 Athenians were participating in government. Five hundred years before the Common Era, the largest and wealthiest agrarian civilization in the world was the Persian Empire. It conquered some of the Greek colonies on the shores of Anatolia but when the Athenians fought the Persians, they won — on land at Marathon in 490 BCE and in great sea battles. A runner, Phidippides, carried the news of victory the 26 miles from Marathon to Athens and died after shouting, “Rejoice, we conquer.” (The day before he had run 140 miles to Sparta and back, asking for help, which for religious reasons the Spartans wouldn’t give until the Moon was full.) Phidippides’s effort 2,500 years ago also spawned the 26.2-mile marathon running races that are so popular today. After their victory over the Persians, Athens enjoyed a golden age of cultural creativity of some 150 years. The high tide of democratic participation took place under the elected general Pericles, who served 32 years in the mid-fifth century. Athenian merchants had earlier brought knowledge and ideas from Mesopotamia and Egypt; Athenian scientists, philosophers, and playwrights developed and combined cultural traditions that would later spread throughout Europe and serve as a foundation for Western culture. (Just for reference: the philosophers Socrates died in 399 BCE, Plato about 348 BCE, and Aristotle in 322 BCE.) Of course, most Greeks did not have an advanced education; the literacy rate for that time is estimated at about 5 percent. The more educated Greeks believed in a pantheon of gods, headed by the sky god, Zeus, who emerged triumphant from the battle of the gods. (See the Greek origin story in Unit 1.) Many Greeks believed in mystery religions, which involved secrets known only to initiates and often entailed a savior whose death and resurrection would lead to salvation for followers. Greeks attacking Persian ships© Bettmann/CORBIS The Greek city-states never figured out how to live together peaceably; instead, Athens and Sparta fought the Peloponnesian War (431–404 BCE), in which Athens was defeated and all city-states were weakened. In the mid- 300s BCE, Macedonia, their neighbor to the north, conquered the Greek cities. When the Macedonian leader, Philip II, was assassinated in 336 BCE, his 20-year-old son, Alexander, took the stage. In 13 amazing years, Alexander conquered enough land to form the largest empire the world had yet seen, from Macedonia and Greece to Bactria (Afghanistan) and parts of India, and including Anatolia, Egypt, the Middle East, Babylonia, and Persia. Alexander died suddenly and mysteriously in 323 BCE after a big drinking party; his empire was divided among three of his generals — Egypt under Ptolemy (not to be confused with the scientist Claudius Ptolemy), Greece and Macedonia under Antigonus, and central Asia under Seleucus. For a little more than a hundred years, these Greek rulers brought Greek culture to their areas. For example, the city of Alexandria at the mouth of the Nile became the most important port in the Mediterranean. The Ptolemaic rulers there funded a museum that served as an institute of higher learning and research; it included a library that by the first century BCE had some 700,000 scrolls. Scholars came from around the Mediterranean to work in Alexandria. There Eratosthenes measured the diameter of the Earth, Euclid wrote the rules of geometry, and the scientist Ptolemy wrote the Algamest, unfortunately ignoring the ideas of Aristarchus, who also studied at Alexandria and theorized almost 2,000 years before Copernicus that the Earth circled the Sun. Meanwhile, over on the Italian peninsula the Romans had developed a powerful agrarian civilization, one that was not fragmented into city-states. Between 215 and 146 BCE they gradually conquered the Greek cities, only to absorb much of Greek culture into their own. Rome and Empire Rome began as a merging of small towns on seven hilltops by the Tiber River, halfway down the west coast of the Italian peninsula. A hundred years after the union, in 509 BCE, Roman aristocrats overthrew their king and set up a republic ruled by the patrician class. (A republic is a form of government in which delegates represent the interests of varied constituencies.) The poorer classes, called plebeians, insisted on some protections and participation. The idea of the republic came to include the rule of law, the rights of citizens, and upright moral behavior. As its population grew, Roman rule expanded. For various reasons — food supplies, defense, land, glory — Roman armies fought the powerful city of Carthage, across the Mediterranean near modern-day Tunis, Tunisia. After 120 years Rome finally won and went on to conquer Greece, Egypt, and the Middle East by 133 BCE. The republican form of government, however, produced seething rivalries among its military leaders, who competed for power with their personal armies. Out of this competition emerged the winner, Julius Caesar (100–44 BCE), who conquered Gaul (modern France) and England, but not Scotland, Wales, and Ireland, where the Celts held the line. By 46 BCE Julius Caesar declared himself dictator for life, ending the republic. Two years later other members of the Senate stabbed him to death in hopes of restoring the republic. Instead, after 13 more years of civil war, Caesar’s adopted son, Octavian, known as Augustus, took the throne and ruled for 45 years virtually unopposed. The empire reached its height in the first two centuries of the Common Era. From 27 BCE to 180 CE, a time known as the Pax Romana, or Roman Peace, Roman leaders controlled about 130 million people across an area of about 1.5 million square miles, from a city of 1 million people. Roman roads linked all parts of the empire. Roman law, which featured key concepts such as the principle that the accused are innocent until proven guilty, was administered everywhere. Under Roman law men had most of the rights, as was also the case in Greece. The father of the Roman family could arrange the marriages of his children, sell them into slavery, or even kill them without punishment. Roman law limited women’s rights to inherit property and assets, but some clever individuals managed to skirt this law. Like all agrarian civilizations of its time, Romans made use of slave labor — but on a larger scale than most. No reliable data exist, but at the height of the empire maybe one-third of the population were slaves; an emperor alone might have about 20,000 slaves. In 73 BCE an escaped slave, Spartacus, assembled 70,000 rebellious slaves; after several years Roman troops crushed them and crucified 6,000 survivors along the Appian Way. Romans put more of their creativity into roads, aqueducts (for carrying water), and law than into philosophy and science, unlike the Greeks. In a way, though, the Roman Empire was a vehicle for the spread of Greek culture. The Romans honored many gods, renaming the Greek ones and taking them as their own. Roman statesman Marcus Tullius Cicero (106–43 BCE) adopted a version of Stoicism, a Greek philosophy seeking to identify universal moral standards based on nature and reason; Epicetus and Marcus Aurelius further popularized it. The older mystery religions — the Anatolian rites of Mithras and Cybele and the Egyptian rites of Isis — proved immensely popular in the Roman Empire. Out of a remote corner of the Roman Empire emerged a small sect that has become the most widespread religion of today’s world — Christianity. The Romans conquered Judea (modern Israel) in 6 CE. Jesus, whom Christians consider the Son of God, grew up at a time of great tension between the Roman overlords and their Jewish subjects. The Romans allowed Jesus to be crucified in the early 30s CE to forestall rebellion, which they believed he was advocating with his message that “the kingdom of God is at hand.” In 66–70 CE the Jews actually did revolt against Roman rule; the Romans crushed this by destroying the Jewish temple, taking thousands of Jews to Rome as slaves, and sending most of the rest into exile. After this revolt, Christianity spread to non-Jewish communities, led by Paul of Tarsus, Anatolia, who preached in the Greek-speaking eastern regions of the Roman Empire. At first Rome persecuted Christians, but by the third century CE Rome had become the principal seat of church authority, with the religion appealing to the lower classes, women, and urban populations. In 313 CE Emperor Constantine (who ruled from 306 to 337 CE) legalized Christian worship after his own conversion, and by the end of the fourth century it had become the official state religion. Zeus being crowned by Victory© Bettmann/CORBIS History books used to refer to the “fall” of Rome in 476 CE when a Germanic general, Odovacar (435–493), became the ruler of the western part of the empire. But the fall was a gradual dissolution, not a sudden collapse. After 200 CE, Rome faced many problems. Strong leadership was lacking; during a 50-year span in the 200s CE there were 26 emperors, only one of whom died a natural death. Epidemics of disease spread along the Silk Roads; afflictions that began in animals — smallpox, measles, mumps, whooping cough — could spread rapidly in urban populations. The Roman world lost about one-quarter of its population before 450 CE. Monetary inflation occurred; people lost confidence in coins and returned to bartering. The dissolving empire meant the decline of urban life, reduced international trade, loss of population, and widespread insecurity for ordinary people. In 324 CE Emperor Constantine moved the capital to Byzantium (renamed Constantinople and now called Istanbul) in Turkey, and from there the Eastern Roman Empire became the Byzantine Empire, which lasted another thousand years until the Ottoman Turks sacked Constantinople in 1453. The Western Roman Empire ended in 476. Centralized authority did not hold; government reverted to city-states and small territories ruled by princes, bishops, or the pope, with the Roman Catholic Church often at odds with state authorities. The common tongue, Latin, evolved into many splinter languages — French, Italian, Spanish, Portuguese, and Romanian. Scholars in the Library of Alexandria© Bettmann/CORBIS Connections and Legacies Even so, Greco-Roman collective learning managed to live on. Much credit must go to the Ptolemaic rulers in Egypt, who supported scholarship and research at the Museum and Library of Alexandria. Nobody knows for sure what happened to Alexandria’s library, but eventually it disappeared. The part of the city where it stood now lies underwater; in 2004 excavators discovered 13 lecture halls. Three main claims have been made about the library’s destruction: that Julius Caesar accidentally, or on purpose, set part of the city on fire in 48 BC when fighting his rival general, Pompey; that Christians destroyed it in the early fifth century CE; and that Muslims, who took Alexandria in 640 CE, ransacked the library and burned the documents as tinder for their bathhouses. (This was written 300 years after the purported event by a Christian bishop known for describing Muslim atrocities without much documentation.) Possibly all of these events, or versions of them, contributed to the library’s eventual demise. Whatever documents were at hand, Muslim scholars became interested in Greek ideas. These scholars spread their learning across North Africa and into modern Spain. In the 11th century, Latin Christians took Toledo and Sicily back from the Muslims, and southern Italy from the Byzantines, acquiring many manuscripts written by Greek and Muslim scholars and monks. In the 12th century the Muslim scholar Ibn Rushd (1126–1198 CE), known as Averroes in Latin, wrote commentaries on the Greek philosopher Aristotle and included some Arabic translations of the original Greek. By 1300, universities had been organized in many European cities, through which Greco-Roman ideas entered European intellectual life. Scholars in the Byzantine Empire also played a large role in preserving Greek knowledge. During the centuries when scholarship disappeared in the western part of the former Roman Empire, Byzantine monks and academics copied and recopied the Greek manuscripts. The Roman legacy seems a bit more concrete. Hundreds of miles of Roman road still exist, after 20 centuries of use. Emperor Justinian (reigned 527 – 565 CE) reorganized Roman law with the Code of Justinian, which is still the basis of legal systems in most of Europe. (U.S. law is based on English case law.) Humanists in Europe used the ideas of Roman non-Christians, especially Cicero, to discuss how to live well rather than arguing about theology. The names of our months also derive from Roman times, carrying the names of their gods and of a couple of their most famous emperors. Perhaps the most important legacy of Greco-Roman civilization is its experiments with male citizen participation in political life. Though these exercises seem rather short-lived in both societies, the ideas later reemerged in Europe and the fledging United States to play a significant role in the shaping of modern governments. Greco-Roman timeline. Click here for a larger version. Download PDF. Now that you’ve read all of the articles and filled out the Civilization Comparison Chart, check your answers against the answer key to see how well you did! [Sources and attributions]

Aksum By David Baker The Aksum Empire was the result of two world hubs sharing their collective learning about agriculture, and rose to become a great power in the ancient world because it formed a crucial link between East and West on the supercontinent of Afro-Eurasia. East Africa East Africa was the cradle of our species. For millions of years, many of our hominine ancestors roamed across the land. It is ultimately the homeland of every human being spread across the planet. Additionally, East Africa was the region that birthed one of the mightiest of African civilizations: the Aksum Empire. At its height in the third cen- tury CE, some ancient writers deemed it one of the four great powers of the world, alongside Rome, Persia, and China. Thanks to its position in the web of collective learning in Afro-Eurasia, it rose to become one of the most complex agrarian civiliza- tions of the ancient African world. African agriculture, in general, got a late start. It was invented independently on the other side of the continent in West Africa, around 3000 BCE. This “lags behind” the Fertile Crescent by several millennia. The transition from foraging to agriculture did not happen easily in Africa because, for one reason, humans evolved there and the environment was well suited to that mode of life. Also, because of the “trap of seden- tism,” humans were reluctant to transition to a less healthy, more miserable form of life like early agriculture, if they could help it. So agriculture appeared late in West Africa. What is more, agricultural knowledge didn’t spread out from West Africa until about 2,000 years later. However, the peoples of East Africa were the recipients of collective learning from not only West Africa, but from the much earlier centers of agrarian knowledge in Egypt and Southwest Asia. Collective learning from two agrarian hubs The region known as the “Northern Horn” of East Africa kept up with foraging for many thousands of years after the dawn of agriculture in the Fertile Crescent. But as agrarian civilizations in that region grew larger, communications to the distant land of the Northern Horn also continued to grow. Knowledge of farming filtered down from Egypt and Southwest Asia and the peoples of the Northern Horn began to adopt a mixture of foraging, plant domestication, and animal herding. They domesticated ensete, a type of banana, at a very early point, perhaps as early as 3000 BCE or more. The people of the Northern Horn foraged for animal hides, bird feathers, myrrh for use as per- fume, and even obsidian rocks to trade with Egypt. By 2000 BCE, the majority of people in the Northern Horn were semi-nomadic, making use of foraging and domesticated plants and animals. They still used stone tools. Copper and bronze were rare in the region, so they did not go through a bronze age, but instead transitioned directly to iron. Some people in the region still foraged without domesticating anything, but the knowledge transmitted from Southwest Asia and Egypt created a mixture of the two lifeways of foraging and agriculture. To the south, the rest of Africa would transition to agriculture much more slowly. But East Africa was jolted by two major hubs into the agrarian era. By 1000 BCE, hunting and gathering was on the decline, and agriculture was becoming increasingly dominant. Southwest Asia had transmitted the knowledge of wheat and barley, and introduced them into the region. East Africans domesticated a local variant, teff, for similar use. These three formed the major East African crops. Mean- while, the Bantu peoples of West Africa arrived, and two centers of independent agri- cultural learning converged in East Africa. The Bantu brought with them knowledge of sorghum and millet. It is around this time that the agricultural way of life solidified itself in East Africa, bringing the human history of foraging in the region, which stretches back hundreds of thousands of years, mostly to a close. Early East African states Around the same time, a major agrarian civilization arose in the Northern Horn, popularly known as D’mt. This mysterious kingdom flourished from the tenth to the fifth centuries BCE. They formalized and intensified their trade relations with Egypt. They began developing mass exportation of agricultural goods, along with intricate stone jewelry. When the kingdom of D’mt fell, smaller kingdoms populated the area. These kingdoms adopted iron and began exporting their metal work. Collective learning arrived from Arabia and Egypt, influencing Aksum’s architecture and material culture, increasing the literacy of its people, and introducing the pre-Islamic Arab religion, which worshipped many gods. For many years, Aksum was just a tiny settlement in the Northern Horn, slowly acquiring more land and wealth from trade. Then in 30 BCE, something decisive happened. The Romans under Augustus conquered and annexed Egypt. Aksum was brought into contact with the Roman world in the Mediterranean. Trade routes shifted from the Persian Gulf and overland Asian routes more to the Red Sea. Aksum soon became a hub of overseas trade between the vast Roman Empire and the states of India. It grew as a prosperous connection for the transmission of trade goods and collective learning across the entire supercontinent of Afro-Eurasia. Aksum at the center of Afro-Eurasia Becoming a mercantile power can transform a small state into a powerful kingdom very quickly. Aksum managed trade between India and the Mediterranean in ivory, gold, emeralds, silk, spices, agricultural products, salt, exotic animals, manufactured goods, and much more. In the first century CE, Aksum flourished. They could afford to build a powerful navy to patrol the Red Sea and protect their trade routes. It was at this time that Aksum was first mentioned by Greco-Roman scholars. Aksumite civilization continued to grow in wealth, power, and complexity. Aksum’s capital showed signs of rapid growth. It was a loose collection of impressive buildings and burial grounds. The town grew so rapidly that there seems to have been no master plan for the city’s layout, or the designation of city walls for where the city would stop growing. Aksum built many grand monuments, and the wealthiest citizens were buried in elaborate tombs marked by huge stone pillars, called stelae, with intricate carvings upon them. Aksum had a division of labor: bureaucrats, priests, soldiers, merchants, and artisans. It had its own coinage, each dynasty etched onto the gold coins, and these have been found by archaeologists across the Old World from Rome to Persia to India. Being a naval power, Aksum was able to transport troops and expand its frontiers. The third century CE marks a period of intense military expansion. At its height, the Aksum Empire controlled North Ethiopia, parts of Sudan, the southern Arabian peninsula, most notably Yemen. With wealth to hire swords and ships, and no comparable power in East Africa to oppose them, the Aksum Empire was one of the true powers of the ancient world, and one of the first complex agrarian civilizations in Africa. In the fourth century CE, Aksum formally adopted Christianity as its state religion, linking it culturally to the Roman Empire, which had also officially made Christianity its state religion. As a hub of trade in the ancient world, Aksum was also a frequent witness to the technological developments transmitted across Afro-Eurasia. Image of ancient stelae field in Aksum, Ethiopia. Range of the Aksum Empire in East Africa. The fall of Aksum Aksum continued to prosper long after the Western Roman Empire declined and fell in the 400s, but its imperial ambitions were also definitely part of its own downfall. Launching another series of military campaigns to subdue Yemen again in the 500s, they exhausted their treasury. Eventually they were booted out of Yemen, never to re- turn. Meanwhile, the Aksum elite were embroiled with infighting, weakening the state. Another blow fell with the Justinianic Plague around 541 CE, a hugely destructive plague that scholars are fairly certain was the same disease, Yersinia pestis, that caused the Black Death. Aksum still had its revenues from trade between India and Byzantium (transformed from the Eastern Roman Empire) and still did not fall, though its territory had been reduced. In the 600s, however, the Islamic conquests further weakened Aksum. As Arabian armies spread across the Old World, Aksum managed to fight them off. However, the Christian empire suddenly found itself isolated economically and politically. This meant that the main source of Aksum’s strength – trade – was taken away. The gradu- al drying of the climate in the Northern Horn also reduced the capacity of Aksum agri- culture, the number of people they could support, and the revenues they could get from taxing the land. Nevertheless, Aksum limped on for another few centuries, its glory days behind it, but its independence intact. All told, this East African agrarian civilization survived for nearly a millennium. Then around the year 960 CE, Aksum’s royal family was overthrown by an unknown female usurper. Legend has it was a Jewish queen named Gudith, but evidence is sparse for that. We do know that at this point the Aksum dynasty came to an end. Their successors, the Zagwe dynasty (est. 900, r. 1137-1270), similarly lived isolated from the world, no longer the recipients of the Afro-Eurasian network of collective learning. The same goes for the Solomonic dynasty (1270-1529) that followed them were also fairly isolated though they eventually fell under the influence of Portuguese colonists and fought many wars against the surrounding Islamic states. Lessons in collective learning The Aksum Empire is a curious case for Big History. It was the recipient of collective learning from two independent regions that gave birth to agriculture: the Fertile Cres- cent and West Africa. For many centuries, East Africa bore a strange mixture of agri- culture, pastoralism, and foraging. After the full transition to agriculture was achieved around 1000 BCE, East Africa quickly progressed to agrarian states, rather than hav- ing a long period of early agriculture like in other regions. This also may be the result of knowledge for social organization transmitted from Southwest Asia. More than that, a millennium later, Aksum arose as a very powerful empire in the ancient world, the recipient of collective learning along trade routes of Afro-Eurasia. The transformation of East Africa, in just 2,000 years, from the cradle of humanity still foraging and using stone tools, to a powerful ancient empire wielding blades of iron and ruling the seas, is testament to the power of collective learning and the networks of the Afro-Eurasian supercontinent. Once the “energy bonanza” gets underway, it can spread rapidly to other regions and quickly increase human complexity. After the Islamic conquests of the 600s, however, Aksum was cut off from that net- work of collective learning. This stands in sharp contrast to the Ghana Empire of West Africa which continued to grow in strength and wealth by open trade with the Islamic world. A network of collective learning has the power to make or break human civilizations. Once East Africa entered the unified global system of the modern era, it suffered numerous hardships that were shared by other peoples in sub-Saharan Africa. And today, the challenges that face East Africa are some of the most concerning of our age. It is our challenge to help East Africa to fully enjoy the benefits of a global network of collective learning, rather than suffer from the inequalities such a network can sometimes cause. The Aksum Empire teaches us one final thing. For several decades, historians had postulated that Aksum was founded by immigrants from Southwest Asia, who brought “superior civilization” along with them. Today, archaeology shows that complex agrarian civilization in East Africa shows signs of developing many centuries before there were any such migrations. Investigations into East African history and the hunt for empirical evidence have dispelled the myth that the African peoples were “historically incapable” of producing powerful agrarian states. The examples of Aksum in East Africa and Ghana in West Africa disprove such claims. While the entry of sub-Saharan Africa into the agrarian era was later than Southwest Asia and Egypt, once they adopted agriculture, agrarian states arose very quickly. This was no small feat in a region of the world where humans evolved and had adapted to the environment as foragers for hundreds of thousands of years, and millions of years for the ancestral species that came before them. While sub-Saharan Africa suffered greatly during the Modern Revolution, it must not be forgotten that for centuries in the ancient and medieval world, the states of Africa stood at the highest point of complexity that humanity could offer, and also the highest point of complexity in the grand narrative of the Universe to that point. It remains to be seen if all regions of the world can share in the collective learning of a global system, to reach even greater heights of complexity in our common story. [Sources and attributions]

The Origin Of Agriculture In Africa By David Baker, Adapted By Newsela Sub-Saharan Africa is notable for the unusual path it took into the agrarian era, much of it affected by the fact that it is the homeland of humanity itself. Agriculture: why wasn’t Africa first? As long as humans have existed, some of them have always called Africa their home. We evolved in Africa from a long lineage. Homo erectus, Homo habilis, and Australopithecus are just a few milestones over the past 3.5 million years – many times longer than Homo sapiens have existed (approximately 200,000 to 250,000 years). Africa is the cradle of our species, and our first home. In fact, we are a very closely related family, much more than usual in nature. DNA testing tells us that a disaster 74,000 years ago, which many think was the super-eruption of Mount Toba, reduced the hu- man population to a few thousand. That was 10,000 years before the biggest human migration out of Africa. As a result, there is more genetic diversity between two different groups of chimpanzees separated by a few hundred miles than there is in the entire human species now spread across Earth. With humans having spent such a long time in Africa, and with such a “recent migration” out, why didn’t something like agriculture evolve there first? The Fertile Crescent developed agriculture first, about 9000 BCE. On the other side of the world, China and New Guinea followed in 7000 BCE. For thousands of years, the only part of Africa to have agriculture was Egypt, interacting closely with Southwest Asia. All of Africa below the Sahara practiced hunting and gathering until approximately 3000 BCE. Why did sub-Saharan Africa lag behind the Fertile Crescent by 6,000 years, despite the fact that hu- mans had lived there for about 200,000 years? Was there some sort of disaster that wiped out earlier attempts at farming without a trace? Was there some sort of “failure” in the collective learning of the people there? Why didn’t the first farms, the first cities, and the first empires emerge in sub-Saharan Africa, where our ancestors had roamed and innovated for hundreds of thousands of years? Continent of Africa. African “fine-tuning” In fact, Africa developed agriculture a little later because it was the cradle of our species. Humans evolved in Africa, alongside the many other animals there. That meant that for millions of years, these animals had evolved to cope with Homo habilis, Homo erectus, the Neanderthals, Homo sapiens, and many others in their environment. It is the same reason why tons of megafauna still exist in Africa, whereas much of it was wiped out in Australia and the Americas when humans arrived there. Animals need generations to adapt their instincts to humans. African animals had a lot of time for that adaptation so it was much more difficult for humans to domesticate a wide variety of animals, and that domestication is one of the first crucial steps for farming. It also works the opposite way. Humans had evolved in Africa as foragers. In fact, earlier human species foraged for millions of years. This was our way of life for most of our history, and for people in Africa, for the longest time it was the best way of life. Over many generations, humans were keenly adapted to their environment, forming an intricate part of the ecosystem there. This was very different from many other regions of the world, where humans suddenly cannonballed in, creating all sorts of ecological ripples and facing environmental challenges to which they were not naturally well adapted. Over long stretches of evolutionary time, humans had learned to live with Africa and Africa had learned to live with humans. “Gardens of Eden” and the “Trap of Sedentism” Life as an early farmer was an ugly deal. It was one that humans tried to avoid if they could. It was usually only with a “trap of sedentism” that humans abandoned foraging and started to farm. As farmers, humans had to spend more time actually working (one estimate is 9.5 hours a day as a farmer; 6 hours a day as a forager). The result of early farming was more disease, worse nutrition, worse health, and greater vulnerability to climate and ecological disasters. For instance, we know that for the longest time, foraging communities in the Kalahari Desert in Southwest Africa knew about farming but didn’t adopt it. Why would anyone adopt a way of life that was far less healthy, far more work, and generally much more miserable than foraging? Africa is a beautiful and diverse continent, but it also contains many challenging environments. The north has the deadly and harsh Sahara, which makes a transition to agriculture unlikely. It also cuts off a lot of communication with earlier agricultural societies, and in fact sub-Saharan Africa had to come up with farming independently, in West Africa, below the desert. Also, there are many dense malarial forests that would be very difficult for foragers to clear, settle, and farm, even if they wanted to. Finally, diseases also had evolved alongside humans in Africa, and there were many tropical diseases that made it a good idea for humans to keep moving rather than settle down. Another factor contributing to the long absence of agriculture in Africa is the lack of so-called “Gardens of Eden,” regions so lush and abundant with life that foragers would settle there and no longer need to travel for a generation or so. Eventually, they would exhaust the land and fall into the “trap of sedentism.” This may have happened with the Natufians in the Fertile Crescent. In Africa, there weren’t many, if any, “Gardens of Eden.” Humans had roamed from region to region as foragers for hundreds of thousands of years, entering one area, feasting on the resources, then moving on to another region while the old one naturally replenished itself over several years. Sub- Saharan Africa simply did not have many (or any) of those tempting “traps” to force humans into early farming. The independent origin of African agriculture However, farming did eventually emerge independently in West Africa in about 3000 BCE (some estimates state even a little earlier), in the fairly lush and habitable savanna on the border between present-day Nigeria and Cameroon. It is possible there finally was a “Garden of Eden” there to “trap” people into early farming. However, many scholars argue that even here, farming began as a way to support the development of animal husbandry rather than to meet a demand for food. West Africans had begun to domesticate wild cattle several thousand years before they started to farm. The advantage of herding cattle to a group that was on the move, foraging from place to place, is obvious. You can take your food source with you. If you can breed your food, you’ve got a renewable supply of meat. If you can grow a bit of food when you’re foraging in an area for a few months, you can sustain your animals on simple grains while you forage for more nutritious food sources. It seems pretty clear that the beginnings of West African plant domestication were fairly piecemeal. Eventually, however, West Africans began to settle and grow their food full-time. From 3000 BCE to 1000 BCE, the practice of farming spread across West Africa. They grew millet and sorghum (plants used for grain and fodder), and later began growing a special strain of rice native to Africa. They also grew tubers (root vegetables), yams, cowpeas, and oil palms, and began mass producing all sorts of succulent melons and fruits. Because early West African farming methods are unique in a lot of ways and they made use of many crops only native to Africa, scholars have determined that farming in West Africa was not derived from Egypt or the Fertile Crescent. It would appear West Africa is another one of those regions that mysteriously started farming independently. In fact, West Africa started this whole process around the same time it had begun in the Americas, and before it had begun in many other regions of the world. The spread of African agriculture (1000 bce-500 CE) Sorghum and millet were the number one crops of West Africans, and they continued to put a lot of emphasis on cattle herding as well. This played a role in a great migration of farmers out of West Africa starting approximately 1000 BCE. These migrants were the Bantu people, who spread farming across the rest of the continent. Some of them traveled along the verdant grasslands of the Sahel, a strip of land just below the Sahara. This was a corridor to East Africa, where the Bantu arrived around 1000 BCE, bringing their farming methods with them. The East Africans had already domesticated a few plants, such as enset (a kind of banana). Around this time, the Africans had adopted the use of iron technology, producing useful weapons and sturdier farming tools, particularly from the major iron production sites near Lake Chad just to the northeast below the Sahara, and Lake Victoria, in the lush regions of East Africa. Meanwhile, other Bantu wandered out of West Africa and headed south, and by 500 BCE had reached the Congo region. Finally, the Bantu in East Africa migrated south all the way to the end of Africa, arriving in Natal, the lands of the Zulu, by 500 CE. By that time, farming had spread all over the continent, except to the harshest environments and densest forests. Most foraging communities became absorbed by these herding/ farming peoples. It’s interesting to note that the Efik origin story, which you read in Unit 1, talks about people defying the gods and beginning to farm exactly in the region where farming did begin. Also, the Zulu origin story speaks of a long journey south from the “reed” lands to the north, when their people did indeed migrate down from East Africa. The spread of agriculture across sub-Saharan Africa is reflected in the sudden jump in population around this time. West Africa remained the most populous, thanks to its early start, and it remains so today. In 500 BCE, it is estimated sub-Saharan Africa had a population of only 7 million. This is quite low and is due to the fact that foragers need a lot of land to support themselves because they stay on the move, searching for food sources, rather than intensifying the output of a single stretch of land. By 500 CE — in the space of just a thousand years — this number had nearly tripled to 20 million. Bunches of sorghum (bottom) and pearl millet (top right), annual grasses grown as grain in the Sahel Desert, Mali, and West Africa. “Late” African regions, c.1000 BCE-500 CE Sub-Saharan Africa enjoyed the advantages of foraging for a very long time. Even so, West Africa was one of the first regions of the world, after the Fertile Crescent and East Asia, to develop agriculture — and independently at that. However, there was a huge gap of about 2,000 years before farming spread into the rest of Africa. Only from 1000 BCE to 500 CE did the peoples of most regions in sub-Saharan Africa start farming. This is considerably later than some of the other regions of the world. Also, it takes time after the start of agriculture in a region before agrarian civilizations begin. You need time to build up your population. You need time to build up “agricultural sur- plus” to feed cities. The timeline of Africa’s journey into the agrarian era is a mixture of pros and cons. On the one hand, some regions of Africa were at a disadvantage when they encountered European and Islamic cultures in the Common Era. On the other hand, the late start of agriculture in sub-Saharan Africa was a blessing for many people for thousands upon thousands of years. They enjoyed healthier lifestyles and a generally higher standard of living as foragers for much longer than the people of the Fertile Crescent or East Asia. Even after farming was introduced, large regions of Africa escaped the rigid hierarchies, the rule of despotic monarchs, and the widening gap between the rich and poor that characterize agrarian civilizations. A case could be made that between for- aging and modernity, the standard of living for most people got worse. In that sense, Africa enjoyed the advantages of foraging for a long time. Its challenge today is to fully enter and enjoy the advantages of modernity. As the African population continues to rapidly grow, this is a challenge that concerns the entire world as it becomes increasingly interwoven in a single global system. [Sources and attributions]

All of the following terms appear in this unit. The terms are arranged here in alphabetical order. Anthropocene epoch — A new epoch, not formally accepted by geologists, during which our species has become the dominant force for change in the biosphere. The Anthropocene marks the end of the Holocene epoch, about the time of the Industrial Revolution, 200 years ago. Black Death — The fourteenth-century outbreak of bubonic plague, which killed up to half the population of Europe. carrying capacity — The maximum number of individuals that a region’s resources can support or sustain. exchange networks — Networks that link people, societies, and regions through the transfer of information, goods, people, and sometimes disease. All forms of collective learning work through exchange networks. globalization — The expansion of exchange networks until they begin to reach across the entire world. Holocene epoch — The geological epoch that begins with the end of the last ice age, about 13,000 years ago, and ends at the start of the Anthropocene epoch, about 200 years ago. hub region — A geographical region characterized by an exceptional amount of exchange of people, ideas, and goods taking place—Mesopotamia, for example. After 1500, the Atlantic regions became a significant hub region through Europe’s control of the major international sea routes. Industrial Revolution — A period of technological innovation starting in England late in the eighteenth century that resulted in a major change in the way goods were produced, and caused a major shift in global economics. These innovations came as a result of the systematic use of fossil fuels in place of human and animal power to manufacturing, communications, and transportation. Malthusian cycles — Long cycles of economic, demographic, cultural, and political expansion, generally followed by periods of crisis and decline. These cycles, generally lasting several centuries, are apparent throughout the era of agrarian civilizations, and were probably set into motion by the inability of innovation to keep pace with population growth. Named for Thomas Malthus (1766–1834), an English pastor and economist. Modern Revolution — A deliberately vague label for the revolutionary transformations that have created the modern world. The Modern Revolution began around 1500 and ushered in the Modern era of human history. Silk Roads — The trade routes connecting Europe to the Middle East, India, and China. steam engines — Machines that burn coal to produce steam, used to perform mechanical work. James Watt configured the first profitable one at the time of the American Revolution. Their use launched human society over a threshold no longer limited by the annual flow of solar energy. steppe lands — Arid grasslands that are suitable for grazing animals but too dry for agriculture. world zones — Four unconnected geographic zones that emerged as sea levels rose at the end of the last ice age. The four world zones are: Afro-Eurasia (Africa and the Eurasian landmasses, plus offshore islands like Britain and Japan); The Americas (North, Central, and South America, plus offshore islands); Australasia (Australia, the island of Papua New Guinea, plus neighboring islands); and the island societies of the Pacific (New Zealand, Micronesia, Melanesia, and Hawaii).

An Age of Adventure A drawing of Marco Polo © Bettmann/CORBIS By Cynthia Stokes Brown Do you think that long-distance travel is a modern invention? Do you suppose that everyone stayed home until airlines started scheduling flights around the world? Do you think that long-distance travel is a modern invention? Do you suppose that everyone stayed home until airlines started scheduling flights around the world? If so, think again. By the early 1300s, Afro-Eurasia (Northern Africa, Europe, and Asia) had become a world zone in motion. People were traveling everywhere, usually in groups — by foot, donkey, horse, camel, and boat. Merchants moved goods; kings, sultans, and popes moved armies. Diplomats and envoys carried messages; missionaries sought souls. Pilgrims and scholars searched for enlightenment. People looked for work, and whole groups of people migrated for varying reasons. Captains, caravan leaders, travel guides, and transport experts provided the ways and means to keep the multitudes moving. This long-distance travel became easier in the late 1200s and early 1300s largely for three reasons. First, nomads of Central Asia (the Mongols and their Turkish-speaking allies) conquered Russia, China, and most of the Middle East, creating the largest territorial empire the world had ever seen. Their rulers imposed order and security to the trade routes along the Silk Roads. Second, the stability of Islamic rule across North Africa, the Middle East, Persia, and Southeast Asia provided a common civilization for travelers. Third, improvements in sailing technologies increased sea travel in the Indian Ocean. Considering the great numbers of travelers moving across Afro-Eurasia, very few individuals left written accounts of their journeys. We’re left to believe that those who did record their travels must also represent the unknown adventurers who left no accounts. Fortunately, two prodigious travelers, Marco Polo, of Venice, Italy, and Abu Ibn Battuta, of Tangier, Morocco, did leave engaging records of their journeys. They each told their stories from memory, and perhaps some written notes, to others who copied it down. Enough copies were made that some have survived through the centuries. A third traveler featured here, Zheng He, from Yunnan, China, is remembered because he served powerful Chinese emperors. He left brief accounts of his voyages carved in granite, and two officers and a translator who sailed with him left longer memoirs. These three adventurers all traveled within a 162-year time period. Marco Polo started his journey in 1271; Ibn Battuta started his in 1325, just after Polo died. Zheng He made his seven voyages starting in 1403, 37 years after Ibn Battuta died. The extent of these three journeys defies our imagination, even today in the age of jet travel around the world. Marco Polo spent 24 years away from home, traveling most of the time. Ibn Battuta spent 29 years away, visiting the lands of more than 40 modern countries, and covering 73,000 miles (117,000 kilometers). Zheng He was away about 14 years spaced over three decades, making his way around the Indian Ocean and along the eastern coast of Africa. Three adventurers map. Click here for a larger version. Download PDF. Adventurer Comparison Chart Download the Adventurer Comparison Chart and use it  to help compare the three adventurers. Name some of the places they visited and some of the reasons they traveled. Adventurer comparison chart. Click here for a larger version. Download PDF. For Further Discussion Can you think of two examples of how collective learning led to an increase in exploration during the fifteenth and sixteenth centuries?  Share your answers in the Questions Area below and comment on a post with an example that you didn’t think of. [Sources and attributions]

Benjamin Banneker: Science in Adversity By David Baker, adapted by Newsela Benjamin Banneker was a mathematician, astronomer, and polymath, widely regarded as one of the first African-American scientists and a gifted figure during the Age of Enlightenment. The human thirst for knowledge, even in the face of tough circumstances, is reflected in the life of Benjamin Banneker and the life of his family. His grandmother was named Molly Welsh. She was a lower-class Englishwoman from Devon, England. Like many in the agrarian era, Molly was very poor and had to work as a laborer to keep herself fed and sheltered from day to day. She worked as a milkmaid. In 1683, she accidentally spilled a bucket of milk. Molly’s employer did not believe her and accused her of stealing the milk so she could sell it herself. Molly was arrested, found guilty, and sentenced to death. In those days, even petty theft carried a death sentence, under what later would become known as “the Bloody Code.” However, regardless of what the law said officially, in many cases the death sentence was reduced to lesser punishments. In the seventeenth century, the English were still struggling to find people to work in the colonies. So the judge ruled that if Molly could prove she was literate, she would be sentenced to seven years of indentured servitude in the colonies instead. Molly, rare for the lower classes at that time, and even rarer for women, was able to read. She promptly read several passages from the Bible and was packed off to the colonies. Indentured Servitude and Slavery An indentured servant is someone who is compelled by law to work for an employer for a fixed term. They cannot leave their job without being punished. Many English people found themselves arriving in the Americas in such a way in the seventeenth century. Molly arrived in Maryland and spent the next seven years working on a tobacco farm. Part of a contract for an indentured servant is, when they have finished their years of service, they are given land and supplies to start a farm of their own. This was because the English wanted to colonize the vast lands of America as quickly as possible, but not enough people wanted to go over there. Molly was given 50 acres to start life as a farmer. However, managing a huge tobacco farm is difficult for one person to do on their own. She could have hired workers, but there was a labor shortage in seventeenth-century America. The other source of labor was the odious practice of slavery. Molly went to the docks and bought two slaves to help her on her farm. One of the slaves was named Banneka. He had a proud and dignified bearing. He disliked working with his hands. It turned out that Banneka was a prince of the Dogon people of West Africa. But he was captured in an enemy raid and sold to European slavers. He was also very intelligent and brought with him the astounding agricultural knowledge that made the Dogon the envy of the neighboring peoples in West Africa. Molly and Banneka gradually learned each other’s language, and the tobacco farm flourished. Molly and Banneka also fell in love, and Molly freed Banneka and promptly married him. Molly was taking a big risk. One interpretation of the law meant that by marrying a slave, Molly would be assuming slave status herself, rather than freeing her husband. In later life, Molly was walking in town with her children, when a crowd formed around her asking “who they belong to.” Molly did not want to risk her or her children’s freedom and lied, “they are my slave’s children.” Throughout her life, and the lives of her children and grandchildren, the reinterpretation of her marriage to Banneka remained a threat to the freedom and land of the entire family. Molly and Banneka were both extremely intelligent people, who turned their farm into a success. But due to the inequalities of the time, they were limited in how they could share their knowledge with the wider world. The human exchange of learning has been crucial to our advancement throughout human history, from stone tools to skyscrapers. They are just two examples of how inequalities and prejudice can slow down the collective learning of humanity. Molly was a former servant and victim of a harsh justice system, and Banneka was a prince of a proud people in West Africa with great agricultural skills, ripped from his home and sold into slavery. And unlike many with more tragic stories, Molly managed to escape death at the hands of a corrupt justice system and Banneka managed to win back his freedom. Many other potential innovators in human history were not so lucky, and we shall never know what they might have contributed to our collective pool of knowledge. Molly and Banneka had four daughters. The eldest, Mary, was born in 1700. She grew into a tall, beautiful, and very sensible woman. She did not marry for a long time. She could not marry a slave, because that would likely make her a slave as well. Eventually, she married Robert, an African abducted from Guinea, whose story is a bit foggy in the sources. In one version, Robert was bought by Molly and Banneka and freed once they noticed he loved their daughter. In another version, Robert was taken from Guinea and escaped slavery several times, before being sold to a planter who freed him, and then making his way to Baltimore County. At any rate, Mary and Robert married as free people, and took the last name Bannaky. Slave market A Truly Gifted Child Robert and Mary also proved themselves to be knowledgeable and successful farmers, who made enough money to continue buying more land. In 1731, they had a son, Benjamin. Banneka had died in the 1720s. Molly took a close interest in educating the young Benjamin. She taught him to read and passed on the African farming techniques of Benjamin’s grandfather. Benjamin grew up to be quiet, intelligent, and well-spoken. He could quote long passages from literature, to the astonishment of the locals who met him. By the age of 6, Benjamin could even do basic accounting for the farm and for some of the nearby neighbors. As smart as his parents and grandparents were, Benjamin was a truly gifted child. Robert continued to be successful and, in 1737, he bought an additional 100 acres and put his name and the 6-year-old Benjamin’s name on the deed. This was to make sure Benjamin would inherit the farm without anyone giving him any trouble. The farm was higher up in the hills, far away from too many neighbors, and it gave the family a quiet life with a great deal of privacy. Benjamin continued to progress as a gifted child. He impressed a Quaker farmer, named Peter Heinrich, who was starting up a school in the area. Benjamin soon surpassed his teacher’s skills, and was allowed to plan his own lessons. Benjamin attended school for a year or two at most. Then, he started full-time work on the tobacco farm. Heinrich still took a keen interest in his education, however, and the school loaned many books to Benjamin. From this point forward till the end of his life, Benjamin was largely self-taught. Benjamin studied classical history and developed an eloquent writing style. But his real passion was for the sciences and mathematics. Benjamin would create complex math problems for himself and then puzzle over them until he solved them. With only a few books, Benjamin taught himself mechanical engineering, algebra, geometry, and trigonometry. As his father, Robert, got older, Benjamin (now adopting the last name Banneker) began to take over more and more work on the farm. By this time, Benjamin had already become a mathematician, scientist, and polymath. When Benjamin was 22, a man named Josef Levi visited the farm from England. Josef had a watch, which was a rare sight in those days. Most people told time by the position of the Sun in the sky. Benjamin was fascinated by it. Josef lent it to him, intending to collect it when he returned from England. But he unfortunately died at sea and never returned. Benjamin took the watch apart, sketched it, and figured out exactly how it worked. He then took some hardwood and began carving out copies of the watch’s parts. Benjamin assembled a clock. So rare were clocks in the 1700s, it was the first clock in U.S. history to be made entirely from parts made in America. It worked perfectly for 50 years. Thereafter, Benjamin often repaired all types of clocks and watches for his neighbors. In 1759, Benjamin’s father, Robert, died. Benjamin ran the farm himself. In his spare time, he continued to read, played flute and violin, and read letters for his illiterate white neighbors. He never married. Had Benjamin been born even a century later, he might have had an opportunity to attend school, even a university, and contribute to mathematics and scientific advances. As it was, at a time when the Enlightenment and Scientific Revolution was in full swing in Europe and America, Benjamin’s circumstances made it difficult for him to contribute to the pool of human knowledge. From the age of 28 to the time he was 59, Benjamin lived the life of a farmer and private scholar in Baltimore County. He lived through the American Revolution and was very moved by the calls for liberty, equality, and freedom from tyranny. He also shared the thirst for knowledge of the workings of nature during the Age of Enlightenment. Watching the Stars Meanwhile, in 1772, the Ellicott brothers moved onto the land next to Benjamin’s. They were of European descent from Pennsylvania. Benjamin and the Ellicotts struck a long-lasting friendship. In 1788, the Ellicotts supplied Benjamin with a couple of books on astronomy, along with some equipment. So began Benjamin’s most profound journey into the realm of science. Benjamin continued to teach himself and worked busily on his astronomical calculations. In 1789, he accurately predicted an eclipse would occur on April 14, beating the predictions of many of his contemporaries. In 1790, Benjamin retired from farming. He sold his land to the Ellicotts in exchange for some money and an agreement that he could spent the rest of his life living in his log cabin. Benjamin was finally able to give over all his time to his studies. He began sleeping during the day so he could watch the stars at night. He built a shed and carved out a skylight, turning the shed into a makeshift observatory. Benjamin constructed accurate tables and calculations. His work used an advanced kind of trigonometry. Meanwhile, George Washington was making plans to move the capital of the young United States to what would be named Washington, D.C. Andrew Ellicott hired Benjamin to work on a survey team that would lay down the original borders for the new capital. From February to April 1791, Benjamin’s job was to note star movements and pass the information on to the survey team, so they could very accurately figure out where the borders were by comparison with the position of the stars in the sky. Benjamin also contributed his photographic memory to the drawing of detailed maps and blueprints. Despite his position in the world, Benjamin’s greatest contribution to the pool of knowledge was far-reaching. He calculated the timing of the tides, the time of sunrise and sunset throughout the year, the phases of the Moon, the occurrence of eclipses, predictions for bad winters and seasonal changes, and when pests would be likely to return. He published his calculations in an almanac, along with tips on how to plant crops, ideas for medicine, and some inspiring quotations from literature. An almanac was very important to farmers and sailors in this age. Knowledge of the weather, the tides, and the cycles of the Sun (in a world still largely without clocks) was vital to many people’s livelihoods. Many people in the eighteenth century owned just two books: a Bible and an almanac. Benjamin first published his in 1792 and continued to publish them annually until 1797. They were an immediate success, and won him a lot of admiration. His almanacs were sold widely in the U.S., and a few copies even made it as far as Europe. His most popular bit of knowledge was the tide table for the Chesapeake Bay region. Many of his competitors did not include one, and Benjamin’s other calculations were also often judged to be more accurate. Andrew Ellicott’s plan for Washington, D.C., 1792 Title page to Benjamin Banneker’s Almanac One of the most striking points of Benjamin’s life was to send a copy of his first almanac to Thomas Jefferson, along with a letter. Benjamin found it troubling that a man who advocated for liberty should hold slaves. He wrote: We are a race of beings, who have long labored under the abuse and censure of the world; we have long been looked upon with an eye of contempt. However diversified in situation or color, we are all of the same family. The modern scientific story of humanity bears him out. He sent along his almanac to prove that people of African descent had just as capable minds as any other. In this diplomatic but passionate letter, Benjamin argued: Sir, pitiable it is to reflect that...in detaining by fraud and violence so numerous a part of my brethren, under groaning captivity and cruel oppression, that you should at the same time be found guilty of that most criminal act, which you professedly detested in others. Benjamin considered himself lucky but he was all too aware of the suffering of others. At the time, it is estimated there were “islands” of 8,000 free African-Americans in Maryland, with about 100,000 slaves in the same area. And it would be more than 50 years before Abraham Lincoln’s Emancipation Proclamation. Benjamin’s letter was one of the first in an exchange of letters with Thomas Jefferson, making Benjamin one of the first African-Americans to correspond with a government official. Jefferson responded sympathetically to Benjamin, in the careful way of a politician, and promised to send Benjamin’s almanac to the National Academy of Sciences in Paris. The head of the academy, Condorcet, was a leading figure in the Enlightenment. However, this received no reply. Nevertheless, Benjamin Banneker became famous in his time for his high intelligence and talents. He lived in the world during an important era for science and rational thought. If not for the monstrous prejudices of the time, he arguably would have been even more famous. His talent was profound and his journals reached astronomical conclusions well in advance of his time. In terms of talent, he was undoubtedly one of the greatest scientific minds of the eighteenth century. If awarded a proper position suited to his talents, Benjamin could have contributed greatly to astronomy and the study of many other areas of the natural world. Instead, he lived the majority of his life as a tobacco farmer and private scholar, his legacy go-ing largely unrecognized until about 50 years after his death, and only being fully recognized as late as the 1970s. On October 9, 1806, while taking a walk with a friend, Benjamin said he felt ill and went home to sleep, where he died peacefully. It is a mystery why his cabin burned down on the day of his funeral, along with many of his journals and notes. This was a great loss, not only to our history of the man, but also to the knowledge that could have been useful to his contemporaries. Benjamin’s obituary in the Federal Gazette, three weeks after his death, said: Mr. Banneker is a prominent instance to prove that a descendant of Africa is susceptible of as great mental improvement and deep knowledge into the mysteries of nature as that of any other nation. Benjamin Banneker leaves several legacies. He is widely recognized as one of the first African-American scientists. He serves as an inspiration for the many African-Americans who followed him, working at the forefront of the natural sciences and contributing significantly not only to American history but to that ever growing pool of human knowledge. Finally, Benjamin, his parents, and grandparents, are proof that the collective learning of humanity is robbed of the contribution of many gifted people when society succumbs to corruption, prejudice, and intolerance. When those restrictions are lifted and people are provided with an opportunity to contribute, humanity can progress by leaps and bounds. Every human being is a potential innovator. Living in a world now with 7 billion potential innovators, many of them still suffering inequalities and hardships, the story of Benjamin Banneker is an important one to bear in mind. A 15-cent commemorative stamp honoring Benjamin Banneker, issued February 2015. Timeline of Banneker's Life [Sources and attributions]

Hazards and Hospitality on an Ancient Trade Route The Qinghai-Tibetan Plateau© AStock/CORBIS By Peter Stark The second day into the mountains of the Tibetan Plateau, everything went wrong.  Our canteens ran dry.  We struggled up a mountain pass behind the caravan of yaks that carried our luggage.  It was so steep and high, it felt like we were panting our way up a 15,000-foot-tall black sand dune. Descending the far side, the yaks escaped from the Tibetan herdsman who guided them. Then, trying to round up the yaks, we got separated from each other. I grew dizzy from running in the thin air. Eventually Amy and I found a little trail that led into a deep stream canyon. Then we lost the trail in the canyon’s brushy bottom. That’s when the thunderstorm struck. It was late afternoon. Amy and I were alone in the brushy bottom of the canyon on the left bank of the stream. We didn’t know what had happened to the yak caravan, nor the Tibetan herdsman running alongside them in his long black robe, nor the Tibetan guide on horseback who carried the rifle, nor the Chinese interpreter. We thought they were somewhere ahead of us in the canyon, and maybe on the opposite bank of the stream, but we weren’t sure. Peter Stark traveling through Tibet in a Yak caravan,© Amy Ragsdale The Sky Turned Suddenly Black Lightning rocketed among the mountaintops. Thunder crashed through the canyon, echoing and reverberating, and shaking the ground beneath our hiking boots. White curtains of cold, driving rain swept through the airy space between the canyon walls, obscuring the far side. The stream began to rise — fast — smashing against its banks, churning with whitewater. We followed it downstream, trying to get out of the canyon. Soon we ran into a cliff that rose straight out of the charging water. The only ways past it were to climb high over the cliff or to inch our way across it on narrow ledges. Amy and I started to claw our way up the side of the cliff, grabbing at roots of bushes and moss to hold on. This was what our honeymoon had become. Somewhere up ahead, this canyon was supposed to lead to the headwaters of the Yangtze River — our destination. Soon I was edging out on a slippery, wet ledge, clinging to the side of the cliff, 30 feet above the raging stream. The ledge narrowed. Then it ended in a big nose of rock. I didn’t know where next to place either hands or feet. I was stuck high above the charging stream, growing dizzy looking down between my boots at the spinning rapids below. We were traveling by yak caravan because I wanted to write about the Yangtze River and this was the only way to reach its headwaters in these rugged, mountainous regions of the Tibetan Plateau. Yak caravans like ours, for many centuries, had crossed these high mountains. They traveled on one branch of the ancient trade route known as the Silk Road. The branch across the Tibetan Plateau linked two civilizations, China’s and India’s. Other branches linked Chinese traders with the civilizations of the Mediterranean and Europe, many thousands of miles away. Some writers describe the Silk Road as an ancient highway connecting distant ends of continents. I like to think of it as the Earth’s original Internet. The Himalayan Mountains© Brian A. Vikander/CORBIS When we think of a major highway, we usually imagine someone traveling a long distance by car or bus or truck. But unlike a modern highway, very few people traversed the Silk Road from one end to the other, from China to the Mediterranean, or vice versa. (Marco Polo was one of the famous travelers who did.) The Silk Road really served, like the Internet does, as a linked network of communication “nodes.” In the way “packets” of information are passed along the Internet from computer node to computer node all over the globe, so were actual packets of goods passed from one trader’s caravan to another, and from one caravan post to another on the Silk Road. After months, or even years, these packets had traveled hundreds or thousands of miles along the Silk Road from, say, China to France, a distance of over 5,000 miles as the crow flies, and closer to 10,000 miles by winding roads and paths. The Silk Road. Click here for a larger version. Download PDF. The most famous of these packets of goods traveling along the Silk Road contained, as you might guess, silk. The Chinese had invented this luxurious fabric around 2700 BCE (or earlier) and managed to keep the manufacturing process secret for millennia, closely guarding the silkworm that spins a cocoon of the finest filament — the silk thread. Unraveled from the cocoon, and woven together, the silk threads formed a fabric so soft, so sheer, so refined, that kings and queens, dukes and duchesses, wealthy people of the ancient world, were willing to pay extraordinary prices to possess this luxury good that traveled from hand to hand, caravan to caravan, all the way from China to Europe. Detail from a 12th-century painting attributed to Chinese Emperor Hui Tsung© Burstein Collection/CORBIS Thus Was Born the Silk Road No official “date” marks the opening of the Silk Road, but about 2,000 years ago, during ancient China’s Han dynasty, a government ambassador, Zhang Qian (c. 200–114 BCE), was sent west by the emperor to secure a trade route for silk caravans. Zhang and his officers made peace with some of the nomadic tribes of Central Asia that had previously attacked travelers. After Zhang’s intervention, it became safer for the caravans carrying silk to travel further west, and eventually their trade goods made it all the way to cities on or near the Mediterranean, such as Aleppo, in today’s Syria. They then traveled on sailing ships the rest of the way to the ports of western Europe. Here the fabric was tailored into the gowns and luxury goods of royalty, aristocrats, and wealthy merchants. The new fabric was so thin and sheer and revealing that some Roman authorities considered it scandalous and tried to ban it: “I can see clothes of silk, if materials that do not hide the body, nor even one’s decency, can be called clothes,” wrote the Roman philosopher Seneca the Younger. “Wretched flocks of maids labor so that the adulteress may be visible through her thin dress....” Silk merchants at the bazaar in Cairo, Egypt© Historical Picture Archive/CORBIS Trade traveled both ways on the Silk Road. China desired certain goods, too. From the nomadic tribes of Central Asia, Chinese merchants bargained for horses and cattle, leather and furs, ivory and jade. Silk Road caravans employed pack animals such as camels (able to travel in desert regions), yaks (sure-footed and strong-winded for high mountains), and horses. Each animal carried a load of about 300 pounds (136 kilograms). Trading towns or posts lay at regular distances along the Silk Road, as well as travelers’ inns known as caravansaries, where the caravans could rest the night, resupply with food, or trade their goods. The journey from one end of the Silk Road to the other could take a year. Its many branches ran south to India, to Persia (now Iran), and to Bactria (what is now Afghanistan). Major stops along the ancient Silk Road, such as Baghdad, Damascus, and Kashgar, today remain important trading towns and desert oases. Almost more important than the goods that traveled along the Silk Road were the ideas and inventions that it carried from East to West and vice versa. It is believed that the Chinese were first introduced to grapes and wine, products of the Middle East, via the Silk Road. Music, songs, and stories traveled along the Silk Road, and were shared around the campfires where the camel caravans stopped. So did broad ideas that changed the course of human history. Buddhism first developed in India in the sixth century BCE, and the Silk Road helped carry the faith’s teachings to China and elsewhere, until eventually it became the dominant religion of much of Asia. An Ouigur spice merchant in Kashgar, China, 1994© Reza/Webistan/CORBIS Those many centuries ago, before instant communications, before electronic files and even the printed book, it was difficult to transmit knowledge accurately over great distances. In order to learn, it was best to travel to the very source of the knowledge rather than wait for it to come. Chinese monks traveled along branches of the Silk Road to India so they could read the original manuscripts of the Buddha’s teachings, which were safely kept at monasteries there. One of the most famous Chinese novels, Journey to the West, follows the adventures of a character, Monkey, who a thousand years ago makes this same pilgrimage to read the Buddhist manuscripts. Monkey has to cross a land of deep canyons and towering mountains very much like the Tibetan Plateau, where demons lie in wait for him. Knowledge actually traveled down a road — or even a mountain path. Amy and I, like Monkey, were also tackling a land of deep canyons and towering mountains. As I clung to the point of rock over the raging stream, she called out from behind me. “Do you want me to try?” Amy slithered past me on the wet, slippery rock ledge. (Trained as a modern dancer, she has a precise sense of balance and movement.) She then reached around the nose of rock, groped for a handhold, found one, and, hanging over the rapids, swung herself around the point of rock to the far side. She called back to me, telling me where to put my hand, and I followed. An hour later, we stumbled out of the stream canyon into a much larger canyon. Through it ran a much larger river. This, I gathered, was the headwaters of the Yangtze that we sought. The rain had subsided and misty clouds clung to the gorge’s cliff tops. We balanced across a log footbridge over the churning stream. The footbridge led us to a tiny hamlet of mud-and-stone houses with Tibetan prayer flags draped from house to house, like giant cobwebs. Waiting for us was Lo Da Ji, the Tibetan herdsman who drove our yak caravan; all the yaks; and the Tibetan guide, Ang Ya. We would spend the night in a mud-walled corral surrounded by stables — like an old caravansary on the Silk Road. Our host had constructed the mud corral and houses with his own hands. He was a short but powerfully built Tibetan yak herder with gentle brown eyes. I couldn’t pronounce his long Tibetan name, so I thought of him as “Arnold” because his muscles reminded me of Arnold Schwarzenegger. I’d never been to a spot so remote and so beautiful. Rock ledges towered hundreds of feet over our head, blanketed with grasses and wildflowers like hanging gardens. The big river swirled past the tiny hamlet strung with its graceful web of prayer flags. “What is the name of this place,” I asked, “and how did you come here?” A nomad tending sheep and yaks, Tibet © Craig Lovell/CORBISA nomad tending sheep and yaks, Tibet © Craig Lovell/CORBIS A nomad tending sheep and yaks, Tibet © Craig Lovell/CORBIS Arnold then told us a story. Ang Ya had to interpret it from Tibetan into Chinese for our Chinese interpreter, Little Cheng, and Little Cheng translated it to English for Amy and me. This is how knowledge passed from mouth to mouth, culture to culture. “The name of this place is Ren Zong Da or ‘The Foot of the Valley of the Many Goats.’ Many wild goats used to live on these cliffs. My father lived here, and my grandfather, and before that I don’t know. Many years ago, my mother and her father made a pilgrimage from Tibet to India to visit the birthplace of Buddha. Her father became ill and died in India. To find her way home again, she had to travel alone through the mountains. Bandits stole her horses and her food. She came to this place and a man gave her food and a warm place to sleep. She stayed and married him. That man who helped her was my father.” I was touched by his father’s act of generosity. Arnold now passed on that same generosity to us, giving us a place to sleep in his stables, some warm milky tea, and the makings for a Tibetan yak-meat and yak-milk stew. As we rested and ate at Many Goats, I realized that Arnold’s mother had followed one branch of the Silk Road to India, as Monkey had. Our caravan, wandering through these canyons and mountains, had stumbled across her path. Like all branches of the Silk Road, this one offered adventure and challenge, and had witnessed acts of incredible greed and of incredible kindness. It spanned thousands of miles, thousands of years, and vastly divergent cultures. This ancient route that wound across Asia, I realized, served as a major thread that wove together the peoples of the Earth. For Further Discussion What types of goods were often traded along the Silk Road routes and why? Share your answers in the Questions Area below. [Sources and attributions]

Italian Trader at the Court of Kublai Khan A drawing of Marco Polo © Bettmann/CORBIS By Cynthia Stokes Brown At the height of the Mongol Empire, Marco Polo served Emperor Kublai Khan in China and returned to Venice to write an account of his experiences that would give Europeans some of their earliest information about China. Background In the 13th century, people who lived in Venice, Italy, believed that the Sun revolved around the Earth and that creation occurred exactly 4,484 years before Rome was founded. As Christians, they considered Jerusalem, the place of Jesus’s crucifixion, to be the so-called navel of the world, and their maps portrayed this. Marco Polo was born in Venice, or possibly Croatia, in 1254. Located on the eastern coast of Italy, Venice served as a gateway to the riches of Asia during this era of increasing trade. Goods flowed like water through the city. Ships from around the eastern Mediterranean docked at its port. Merchants and traders set sail from Venice for Constantinople (now Istanbul) and the Black Sea to fetch goods from Russia and from merchants who traveled the Silk Roads, a system of trading routes to and from China that crossed the mountains and deserts of Central Asia. At the time of Marco’s birth, his father, Niccolo, and two uncles, all merchants, were away trading. Supposedly they were visiting cities on the Black Sea, but their adventures had actually taken them all the way to the Mongol capital of China, Khanbaliq (city of the Khan). There they had an audience with the most powerful ruler of the day, Kublai Khan, grandson of the founding emperor, Genghis Khan. When the three Polo men returned to Venice after an absence of 16 years, Niccolo found that his wife had died and that he had a 15-year-old son, Marco, whom he did not know existed. Travels Two years later, in 1271, Niccolo Polo and his brother, Maffeo, set off again, taking the 17-year-old Marco with them. This time they aimed directly for the court of Kublai Khan, to bring him documents from the pope and holy oil from Jerusalem that he had requested. Even with a gold passport from Kublai Khan, which enabled the travelers to use lodgings and horses posted by the Mongols along the Silk Road routes, they took three and a half years to arrive. Upon reaching the summer palace of Kublai Khan in 1275, Niccolo presented his son and offered him in service to the emperor. A 15th-century illustration of the Polos sailing from Venice © Heritage Images/CORBIS A talented young man, Marco had learned several languages along the way, including Mongolian (though not Chinese), and had mastered four written alphabets. Two years before Marco’s arrival, Kublai Khan had completed the conquest of all parts of China and needed non-Mongol administrators in areas that resisted having Mongol authorities. Marco took on various sorts of diplomatic and administrative roles for the emperor from his base in Dadu, which Kublai Khan built next to Khanbaliq. Both Dadu and Khanbaliq stood at what is now Beijing. After more than 16 years in China, the Polos begged permission from Kublai Khan to return home to Venice. Apparently they had proved so useful to the khan that he did not want them to leave. Finally, he agreed for them to escort a Mongolian princess, Cogatin, to become the bride of a Persian khan; thus they headed back west. A miniature painting of Marco Polo before Kublai Khan © Bettmann/CORBIS This time they traveled by sea in Chinese ships and, after many difficulties, succeeded in delivering the princess. Before they could reach Venice, however, Kublai Khan died on February 18, 1294, which allowed local rulers to reassert themselves and demand payment from traders. Consequently, the Polos were forced to hand over 4,000 Byzantine coins, a significant portion of their fortune, to the local government of a city on the Black Sea. Return The Polos returned to Venice in 1295, having been away 24 years. Their enthusiastic biographer told stories, which may have been gossip, that when they returned they were wearing Mongolian clothing and could hardly remember their native language. Their relatives had thought them long dead. But when they produced a small fortune in gems (rubies, sapphires, garnets, diamonds, and emeralds), which had been sewn into the hems of their Mongolian garments, they were warmly welcomed. Soon Venice was at war with its rival city-state, Genoa, on the west coast of Italy. As was custom for a wealthy merchant, Marco Polo financed his own war galley. He was captured during a naval battle and ended up in prison in Genoa. By chance, one of his cellmates, Rusticello from Pisa, had experience writing romantic novels. As Polo entertained everyone with his tales of traveling to China, Rusticello wrote them down in a French dialect. This is how Polo’s accounts, Europe’s primary source of information about China until the 19th century, came into existence. In 1299 Genoa and Venice declared peace; Polo was released and returned to Venice to marry Donata Badoer. The couple had three daughters in quick succession. He spent his remaining days as a businessman, working from home. He died there at almost 70 years of age, on January 8, 1324, and was buried under the church of San Lorenzo, though his tomb has now vanished. Marco Polo’s Book Polo might have been forgotten had his book, The Travels of Marco Polo, not engaged widespread interest. It could be circulated only one copy at a time, since printing in Europe did not begin until almost 200 years later. About 120 to 140 early manuscripts — hand-printed and fragmentary versions of The Travels — survive, and every one of them is different. The earliest readers were scholars, monks, and noblemen. Soon translations of The Travels appeared, in Venetian, German, English, Catalan, Argonese, Gaelic, and Latin. It took more than a century for the book to become part of mainstream European consciousness. Few texts have provoked more controversy than The Travels of Marco Polo. The authorship is not clear — is it Polo or Rusticello? Sometimes the text is in the first-person voice, sometimes in the third-person. How much of the text is based on Polo’s firsthand experience and how much did the author(s) insert secondhand accounts by others? Certainly it’s a mix. What was reported seemed so bizarre to stay-at-home Europeans that the readers often assumed that everything was made up. Yet historians have largely confirmed the facts in Polo’s account of the height of the Mongol dynasty. Polo proved an engaging storyteller. He found Mongolian customs fascinating and reported them enthusiastically, such as the use of paper for money and the burning of coal for heat (see excerpts below). Paper money had been utilized in China for several hundred years, and coal had been burned in parts of China since the beginning of agriculture. A detail from the 1375 Carta Catalana © Bettmann/CORBIS Polo also missed a few unfamiliar practices, notably the books being sold in Quinsa (now Hangzhou), the capital city of the earlier Song dynasty in southern China. Books were widely available there because they were printed with moveable type made of wood, clay, or tin. Moveable type was missing in Europe until 1440, when Johannes Gutenberg, a German printer, invented it there. When Christopher Columbus set sail on August 3, 1492, hoping to find a route by sea to China, he carried with him a heavily annotated copy of The Travels of Marco Polo, expecting it to be useful. The travels of Marco Polo. Click here for a larger version. Download PDF. From The Travels of Marco Polo: Book 2, Chapter 18 OF THE KIND OF PAPER MONEY ISSUED BY THE GRAND KHAN, AND MADE TO PASS CURRENT THROUGHOUT HIS DOMINIONS In this city of Cambalu [another spelling for Khanbaliq] is the mint of the grand khan, who may truly be said to possess the secret of the alchemists, as he has the art of producing money by the following process. He causes bark to be stripped from those mulberry-trees the leaves of which are used for feeding silk-worms, and takes from it that thin inner ring which lies between the coarser bark and the wood of the tree. This being steeped, and afterwards pounded in a mortar, until reduced to a pulp, is made into paper, resembling that which is made from cotton, but quite black. When ready for use, he has it cut into pieces of money of different sizes, nearly square, but somewhat longer than they are wide...The coinage of this paper money is authenticated with as much form and ceremony as if it were actually of pure gold or silver; for to each note a number of officers, specially appointed, not only subscribe their names, but affix their signets also; and when this has been regularly done by the whole of them, the principal officer, deputed by his majesty, having dipped into vermilion the royal seal committed to his custody, stamps with it the piece of paper, so that the form of the seal tinged with the vermilion remains impressed upon it, by which it receives full authenticity as current money, and the act of counterfeiting it is punished as a capital offence. When thus coined in large quantities, this paper currency is circulated in every part of the grand khan’s dominions; nor dares any person, at the peril of his life, refuse to accept it in payment. All his subjects receive it without hesitation, because wherever their business may call them, they can dispose of it again in the purchase of merchandise they may have occasion for; such as pearls, jewels, gold, or silver. With it, in short, every article may be procured... All his majesty’s armies are paid with this currency, which is to them of the same value as if it were gold or silver. Upon these grounds, it may certainly be affirmed that the grand khan has a more extensive command of treasure than any other sovereign in the universe. (pp. 145–147) In this city of Cambalu [another spelling for Khanbaliq] is the mint of the grand khan, who may truly be said to possess the secret of the alchemists, as he has the art of producing money by the following process. He causes bark to be stripped from those mulberry-trees the leaves of which are used for feeding silk-worms, and takes from it that thin inner ring which lies between the coarser bark and the wood of the tree. This being steeped, and afterwards pounded in a mortar, until reduced to a pulp, is made into paper, resembling that which is made from cotton, but quite black. When ready for use, he has it cut into pieces of money of different sizes, nearly square, but somewhat longer than they are wide... The coinage of this paper money is authenticated with as much form and ceremony as if it were actually of pure gold or silver; for to each note a number of officers, specially appointed, not only subscribe their names, but affix their signets also; and when this has been regularly done by the whole of them, the principal officer, deputed by his majesty, having dipped into vermilion the royal seal committed to his custody, stamps with it the piece of paper, so that the form of the seal tinged with the vermilion remains impressed upon it, by which it receives full authenticity as current money, and the act of counterfeiting it is punished as a capital offence. When thus coined in large quantities, this paper currency is circulated in every part of the grand khan’s dominions; nor dares any person, at the peril of his life, refuse to accept it in payment. All his subjects receive it without hesitation, because wherever their business may call them, they can dispose of it again in the purchase of merchandise they may have occasion for; such as pearls, jewels, gold, or silver. With it, in short, every article may be procured... All his majesty’s armies are paid with this currency, which is to them of the same value as if it were gold or silver. Upon these grounds, it may certainly be affirmed that the grand khan has a more extensive command of treasure than any other sovereign in the universe. (pp. 145–147) Book 2, Chapter 23 OF THE KIND OF WINE MADE IN THE PROVINCE OF CATHAY — AND OF THE STONES USED THERE FOR BURNING IN THE MANNER OF CHARCOAL The greater part of the inhabitants of the province of Cathay [now China] drink a sort of wine made from rice mixed with a variety of spices and drugs. This beverage, or wine as it may be termed, is so good and well flavoured that they do not wish for better. It is clear, bright, and pleasant to the taste, and being made very hot, has the quality of inebriating sooner than any other.Throughout this province there is found a sort of black stone, which they dig out of the mountains, where it runs in veins. When lighted, it burns like charcoal, and retains the fire much better than wood; inso- much that it may be preserved during the night, and in the morning be found still burning. These stones do not flame, excepting a little when first lighted, but during their ignition give out a considerable heat. It is true there is no scarcity of wood in the country, but the multitude of inhabitants is so immense, and their stoves and baths, which they are continually heating, so numerous, that the quantity could not supply the demand; for there is no person who does not frequent the warm bath at least three times in the week, and during the winter daily, if it is in their power. Every man of rank or wealth has one in his house for his own use; and the stock of wood must soon prove inadequate to such consumption; whereas these stones may be had in the greatest abundance, and at a cheap rate. (p. 155) The greater part of the inhabitants of the province of Cathay [now China] drink a sort of wine made from rice mixed with a variety of spices and drugs. This beverage, or wine as it may be termed, is so good and well flavoured that they do not wish for better. It is clear, bright, and pleasant to the taste, and being made very hot, has the quality of inebriating sooner than any other. Throughout this province there is found a sort of black stone, which they dig out of the mountains, where it runs in veins. When lighted, it burns like charcoal, and retains the fire much better than wood; inso- much that it may be preserved during the night, and in the morning be found still burning. These stones do not flame, excepting a little when first lighted, but during their ignition give out a considerable heat. It is true there is no scarcity of wood in the country, but the multitude of inhabitants is so immense, and their stoves and baths, which they are continually heating, so numerous, that the quantity could not supply the demand; for there is no person who does not frequent the warm bath at least three times in the week, and during the winter daily, if it is in their power. Every man of rank or wealth has one in his house for his own use; and the stock of wood must soon prove inadequate to such consumption; whereas these stones may be had in the greatest abundance, and at a cheap rate. (p. 155) Timeline of Marco Polo’s life. Click here for a larger version. Download PDF. For Further Discussion What are some similarities and differences between Ibn Battuta and Marco Polo’s travels? Share one similarity and one difference in the Questions Area below. [Sources and attributions]

Throughout human history, different cultures have used boats for transportation, commerce, and warfare. Explore a few examples of the different boats we've used. Roman Galley An 18th-century engraving of a Roman warship © Stapleton Collection/CORBIS The Mediterranean region was one of the first centers of sea commerce as Greek, and then Roman, “galleys” traveled between ports in Europe, Africa, and Asia. The ships were propelled at high speeds by dozens of oarsmen working in unison. With these ships, sails were a secondary form of power. Galleys were used to transport people and goods and were an important instrument of war. In this illustration, the Roman warship pictured has a corvus mounted to its bow. This crane-like machine  was used to damage enemy ships or to lock them to the Roman ship so that Roman soldiers could board them and engage in hand-to-hand combat. Viking Fleet A painting by Edward Moran © Bettmann/CORBIS This painting depicts a Viking fleet in rough seas. Viking “longships” set sail from Scandinavian ports in the Norwegian and Baltic seas beginning late in the 8th century. Among the best sailors of their time, Viking crews plied the North Atlantic and traveled south on major waterways like the Volga River. Archaeological evidence indicates that during several centuries of navigation, the Vikings reached destinations like Greenland and Iceland to the west and distant ports like Nekor (in modern-day Morocco), Constantinople (now Istanbul), and Baghdad to the east and south. The Vikings are thought to have been the first group to actively fish the North Atlantic for cod and Viking ships may have landed in North America hundreds of years before other European explorers like Columbus. Canoe and Schooner A dugout canoe and a schooner © Museum of History and Industry/CORBIS In this 1900 photograph taken off  Washington's coast, Native American whalers paddle their dugout canoe in the foreground while a large schooner passes in the background. Canoes have been used for millennia by many different cultures and continue to be used today. These versatile watercraft are stable in a variety of water conditions and easily transported over land from one body of water to the next. But massive sailing ships like the one seen in the distance are much better suited to long voyages and for the transport of large cargoes. Silver Fleet A squadron from the Dutch West India Company © Bettmann/CORBIS Massive galleons like those depicted here traveled from Europe to the Americas in search of treasure. They often returned to their native countries loaded with silver, gold, sugar, valuable tropical woods, and rare furs. Competing for the new land resources, several European nations staked their claims to colonies in the New World and sometimes fought over control of specific regions. In this engraving, an armada from the Dutch West India Company of Holland captures a Spanish silver fleet off the coast of Havana, Cuba, in 1628. RMS Queen Mary A poster for the Queen Mary © K.J. Historical/Corbis Sailing ships connected the world. But it was steam that took transportation to another level – allowing ships with mechanical engines to move faster and carry heavier loads. The first “steamers” to run regularly scheduled service across the Atlantic made the passage in about 15 days, compared with the two-months required by sailing vessels. From the middle of the 19th century until the late 1960s (when airliners became popular), ocean liners were the primary means of long-distance transportation. The RMS Queen Mary (pictured here) operated from 1936 to 1967. A precursor to today’s enormous cruise ships, the 1,019-foot Queen Mary featured two indoor swimming pools, beauty salons, libraries, nurseries, a music studio, a lecture hall, telephone connectivity to anywhere in the world, outdoor paddle tennis courts, and dog kennels. Submarines An 1859 illustration of the Philips’ submarine © CORBIS The idea of an underwater boat has a long history. According to Greek historian Thucydides, divers cleared submerged obstructions during a siege of Syracuse about 400 BCE and legends tell of Alexander the Great using a “diving bell,” a submersible vessel containing air, about 50 years later. By the early 1700s, numerous submarines had been patented in Europe. A hand-powered military submarine named Turtle was even used in the American Revolutionary War. As mechanical know-how increased, numerous new submarines were designed (including the 1859 craft pictured here). Submarine technology has enjoyed great advances over the last 150 years and now highly engineered underwater vessels have reached the oceans’  greatest depths – the Pacific’s Mariana Trench. Container Ships A Korean container ship in Santos, Brazil © Matt Mawson/Corbis In today’s interconnected world, goods of all types are transported around the world by air, land, and sea. Modern container ships are used for the heaviest loads, carrying manufactured goods, heavy machinery, and vehicles between ports around the world. These massive cargo ships, many more than 1,200 feet long and 150 feet wide, have a load capacity greater than one billion tons. Containers are stacked on the ships’ decks and are loaded and unloaded by giant cranes at harbors in coastal cities.

Chinese Admiral in the Indian Ocean A monument to Zheng He at the Stadthuys Museum in Malaysia, photograph by Hassan Saeed By Cynthia Stokes Brown In the early 1400s, Zheng He led the largest ships in the world on seven voyages of exploration to the lands around the Indian Ocean, demonstrating Chinese excellence at shipbuilding and navigation. Background Zheng He (pronounced jung ha) was born in 1371 in Yunnan, in the foothills of the Himalaya Mountains, 6,000 feet (not quite 2,000 meters) above sea level and two months’ journey to the nearest seaport. As a child Zheng He was named Ma He. Ma He’s father, a minor official in the Mongol Empire, was not Mongol; his ancestors were Persian Muslims. Both Ma He’s father and his grandfather even made the “hajj,” or pilgrimage to Mecca. The Mongols had controlled the Silk Road routes across Central Asia from roughly 1250 to 1350, and ruled China for much of that time too, but the empire then splintered into a number of smaller khanates, each ruled by a different khan. The resulting anarchy and warfare on land encouraged traders to use sea routes and later, by about 1400, most long distance trade was moving by sea. Three years before Ma He’s birth, the Chinese regained control of their empire under the new Ming dynasty. When Ma He was about 10, the Ming army invaded Yunnan to take it back from the Mongols and bring it under Ming control. The Ming soldiers killed Ma He’s father in the fighting and captured Ma He. As was customary with juvenile captives, they castrated him by cutting off his testes and penis with a sword. He survived this trauma and was handed over to be a servant in the household of the emperor’s fourth son, Zhu Di. Castrated men, called eunuchs, were a recognized group inside and outside of China. Emperors, princes, and generals employed them as staff members, figuring this as a way to have male servants serve women without risking the genetic integrity of the ruling family. An unsigned hanging scroll depicting the Yongle Emperor, public domain The prince whom Ma He served, Zhu Di, was only 11 years older than He. They were based in Beijing, in the north of China near Mongol territory, and they spent a lot of time together campaigning on horseback on the Mongolian steppe. Ma He grew unusually tall and strong and became a skilled fighter and brave leader. When the first Ming emperor died, his grandson (the son of his deceased oldest son) succeeded him. In 1402, Zhu Di took the throne from his nephew by force and proclaimed himself Emperor Yongle (“Perpetual Happiness”). He made his companion Ma He the director of palace servants (similar to a chief of staff), and changed Ma’s name to Zheng He in commemoration of his role in battles to win the throne. (Zheng was the name of Yongle’s favorite warhorse.) Yongle ruled from 1402 to 1424. The Seven Voyages Yongle proved extremely ambitious. He temporarily conquered Vietnam and tried to overpower Japan. He built a new imperial capital in Beijing, including the Forbidden City, and extended the Great Wall. Since he was determined to control trading in the Indian Ocean, one of his first acts was to commission the construction of 3,500 ships, with Zheng He supervising the construction and then commanding the fleet. Some of these ships were the largest marine craft the world had ever known. Zheng He’s nine-masted flagship measured about 400 feet long; for comparison, Christopher Columbus’s Santa Maria measured just 85 feet. On the first voyage, from 1405 to 1407, 62 nine-masted “treasure ships” led the way, followed by almost 200 other ships of various sizes, carrying personnel, horses, grain, and 28,000 armed troops. Historians were skeptical of accounts describing the size of these ships until, in 1962, workers on the Yangtze riverfront found a buried wooden timber 36 feet long (originally a steering post) beside a massive rudder. It was the right size to have been able to steer a ship of 540 to 600 feet in length, and the right age — dated at 600 years old — to be from one of Zheng He’s ships. A painting of Zheng He at a temple shrine in Penang, Malaysia © Chris Hellier/CORBIS Zheng He’s initial trip took him from the South China Sea through the Indian Ocean to Calicut, India, and back. The emperor’s purpose for this expedition seems to have been to obtain recognition and gifts from other rulers. The voyagers did not intend to conquer or colonize, but they were prepared to use military force against those who refused to respect them. Near the end of the voyage Zheng He’s ships encountered pirates in the Sumatran port of Palembang. The pirate leader pretended to submit, with the intention of escaping. However, Zheng He started a battle, easily defeating the pirates — his forces killing more than 5,000 people and taking the leader back to China to be beheaded. Five more voyages followed before Emperor Yongle’s death in 1424; they included excursions to Hormuz — the Arab port at the mouth of the Persian Gulf — and the coast of eastern Africa, from which He returned with giraffes, zebras, and other items unfamiliar to the Chinese. On his seventh and final voyage, from 1431 to 1433, Zheng He apparently died at sea and was likely buried off the coast of India, although some of his descendants believe that he made it back to China and died soon after his return. The travels of Zheng He map. Click here for a larger version. Download PDF. Inscribing His Adventures Leaving on his final voyage, at age 60 — the traditional Chinese age of reflection — Zheng He stopped at two places in China to have granite inscriptions placed so that his deeds would be understood and not forgotten. These tablets were erected in Liujiagang (now Liuhe), a port on the Yangtze River, and at Changle, in Fujian province. In the first inscription Zheng He describes his dependence on Tianfei (“Heavenly Princess”), the goddess of Chinese sailors: [We have] traversed over a hundred thousand li of vast ocean [and have] beheld great ocean waves, rising as high as the sky and swelling and swelling endlessly. Whether in dense fog and drizzling rain or in wind-driven waves rising like mountains, no matter what the sudden changes in sea conditions, we spread our cloudlike sails aloft and sailed by the stars day and night. [Had we] not trusted her [Heavenly Princess’s] divine merit, how could we have done this in peace and safety? When we met danger, once we invoked the divine name, her answer to our prayer was like an echo; suddenly there was a divine lamp which illuminated the masts and sails, and once this miraculous light appeared, then apprehension turned to calm. The personnel of the fleet were then at rest, and all trusted they had nothing to fear. This is the general outline of the goddess’s merit...When we arrived at the foreign countries, barbarian kings who resisted transformation and were not respectful we captured alive, and bandit soldiers who looted and plundered recklessly we exterminated. Because of this the sea routes became pure and peaceful and the foreign peoples could rely upon them and pursue their occupations in safety. All of this was due to the aid of the goddess. [We have] traversed over a hundred thousand li of vast ocean [and have] beheld great ocean waves, rising as high as the sky and swelling and swelling endlessly. Whether in dense fog and drizzling rain or in wind-driven waves rising like mountains, no matter what the sudden changes in sea conditions, we spread our cloudlike sails aloft and sailed by the stars day and night. [Had we] not trusted her [Heavenly Princess’s] divine merit, how could we have done this in peace and safety? When we met danger, once we invoked the divine name, her answer to our prayer was like an echo; suddenly there was a divine lamp which illuminated the masts and sails, and once this miraculous light appeared, then apprehension turned to calm. The personnel of the fleet were then at rest, and all trusted they had nothing to fear. This is the general outline of the goddess’s merit... When we arrived at the foreign countries, barbarian kings who resisted transformation and were not respectful we captured alive, and bandit soldiers who looted and plundered recklessly we exterminated. Because of this the sea routes became pure and peaceful and the foreign peoples could rely upon them and pursue their occupations in safety. All of this was due to the aid of the goddess. The “divine lamp” Zheng He mentions is thought be “St. Elmo’s Fire,” the electrical discharge from a ship’s mast that occurs after a storm at sea. On the second inscription, which follows below, Zheng He explains the purpose of the voyages and his gratitude to the sea goddess: If men serve their prince with utmost loyalty, there is nothing they cannot do, and if they worship the gods with utmost sincerity there is no prayer that will not be answered...We, [Zheng] He and the rest, have been favored with a gracious commission from our Sacred Prince to convey to the distant barbarians the favor [earned by their] respectfulness and good faith. While in command of the personnel of the fleet, and [responsible for the great] amount of money and valuables [our] one concern while facing the violence of the winds and the dangers of the nights was that we would not succeed. Would we then have served the nation with utmost loyalty and worshipped the divine intelligence with utmost sincerity? None of us could doubt that this was the source of aid and safety for the fleet in its comings and goings. Therefore we have made manifest the virtue of the goddess with this inscription on stone, which records the years and months of our going to and returning from the foreign [countries] so that they may be remembered forever. If men serve their prince with utmost loyalty, there is nothing they cannot do, and if they worship the gods with utmost sincerity there is no prayer that will not be answered... We, [Zheng] He and the rest, have been favored with a gracious commission from our Sacred Prince to convey to the distant barbarians the favor [earned by their] respectfulness and good faith. While in command of the personnel of the fleet, and [responsible for the great] amount of money and valuables [our] one concern while facing the violence of the winds and the dangers of the nights was that we would not succeed. Would we then have served the nation with utmost loyalty and worshipped the divine intelligence with utmost sincerity? None of us could doubt that this was the source of aid and safety for the fleet in its comings and goings. Therefore we have made manifest the virtue of the goddess with this inscription on stone, which records the years and months of our going to and returning from the foreign [countries] so that they may be remembered forever. Timeline of Zheng He’s life. Click here for a larger version. Download PDF. The Legacy of Zheng He’s Adventures The voyages of Zheng He are a favorite topic of world historians today. They show that Chinese ships could have ruled the Indian Ocean for many more years and possibly been able to sail to the Americas. Why didn’t they? What if they had? How different would the world be? After the final voyage, the Chinese emperor suddenly ordered that these expensive expeditions be halted. The ships were left to rot in the harbors, and craftsmen forgot how to build such large ships, letting the knowledge slip away. The Confucian ministers who advised the emperor distrusted the eunuchs, who supported the voyages. New military threats came from the Mongols in the north and the ministers argued that resources needed to focus on land defenses there instead. Three firsthand accounts survive, written by men who sailed with Zheng He — two from officers and one from a translator. Eventually, Chinese interest in these accounts revived in the 20th century. Prior to that, Zheng He’s exploits were passed on by storytellers who used them as a source of wonder, blending them with other fantastic tales. For Further Discussion Why do you think the Chinese did not actively pursue navigation in the centuries after He? How do you think this affected China’s development? Share your answers in the Questions Area below. [Sources and attributions]

The Graphic Biography below uses “Three Close Reads”. If you want to learn more about this strategy, click here. First read: skimming for gist This will be your quickest read. It should help you get the general idea of what the graphic biography will be about. Pay attention to the title, headings, images, and layout. Ask yourself: what is this graphic biography going to be about? Second read: understanding content For this reading, you should be looking for unfamiliar vocabulary words, the major claim and key supporting details, and analysis and evidence. You should also spend some time looking at the images and the way in which the page is designed. By the end of the second close read, you should be able to answer the following questions: What misconception did the Hawaiians who built the Hōkūleʻa want to change?Why was planning the voyage of the Hōkūleʻa so challenging?What methods did Polynesian navigators use and how was their knowledge passed down?What information does the attached comic, “Aka’s Voyage for Red Feathers” add to the story of Mau Piailug? Why would this story have been useful for Polynesian navigators to learn?How has the artist designed the page, text, and illustrations to tell you about Mau’s story and the story of Polynesian navigators in general? Third read: evaluating and corroborating In this read, you should use the graphic biography as evidence to support, extend, or challenge claims made in the course. At the end of the third read, you should be able to respond to these questions: Can you think of any knowledge that you use in your own life that was passed down to you verbally? Maybe through a family member or older person in your community?Mau’s biography is a story of collective learning. How does it change what you’ve heard about collective learning so far in the course? Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading. The Navigator: Mau Piailug (Graphic Biography) Writer: Bennett Sherry Artist: Argha Manna In the 1970s, Mau Piailug helped revive the navigation techniques ancient Polynesians used to cross thousands of miles of open ocean to settle Hawaii. Download the Graphic Biography PDF here or click on the image above.

Different cultures developed various forms of currency – both as a recordkeeping device and as a medium of exchange. Wheels of Fortune On the isolated Pacific islands of Yap (in Micronesia), a currency developed that was based on wheels of limestone. As the material was not available on the Yap Islands, Yapese had to bring it over from quarries in Palau, an island chain hundreds of miles of away. Portability remains a concern: these Rai stones are sometimes up to 12 feet in diameter and weigh more than 4 tons (more than 8,000 pounds). To save on heavy lifting, Rai sometimes remained in the physical possession of an early owner even if ownership was transferred. In that sense, the stones have significant associations with memory and history and their exchange is sometimes based on a shared understanding. In fact, the value of a specific Rai stone was often tied not just to its size and craftsmanship, but to its history. Although the Yapese now use more conventional forms of money as their everyday currency, Rai stones continue to have symbolic value. Wampum Numerous civilizations around the world have valued shells, and some have made them a form of money. Indigenous people in eastern North America prized the purple and white beads made from whelk and quahog shells, called wampum. The cylindrical beads were originally strung into necklaces and belts and used for recordkeeping. By the time European colonists arrived in the Americas, wampum had evolved into an important unit of exchange among tribes. Realizing their value, colonists began to mass produce the beads to use for trading with the Native Americans. The beads actually gained stature as a substitute for coins in mid-17th century New England but wampum’s lack of inherent value eventually doomed it as a currency. Another type of shells, cowrie, were used as currency in parts of Asia and western Africa until the middle of the 19th century. Bamboo Tally Sticks The history of tally sticks dates back to Paleolithic times. Back then, bones were used to record numerical data, so they were as much a mnemonic device as anything. They continued in use in medieval and pre-industrial times as objects for transactional records and eventually advanced into the equivalency of money. Chinese banks issued bamboo markers instead of regular currency when money ran short during the latter 19th century and during the world wars of the 20th century. The Lydian Lion Most historians agree that the first coins in circulation came from Lydia, in western Anatolia (modern-day Turkey). Production and circulation began around 650 BCE with the casting of electrum, a natural alloy of gold and silver, into small, irregularly shaped pieces that bore a design. The earliest example is thought to have depicted a lion and a sunburst, symbols of Lydia’s then-king. In time, standards for weight and purity were set, and the currency made its way into mainland cities in ancient Greece. Eventually electrum went out of style as coins of gold or silver became the predominant means of exchange. Tang "Flying Cash" Paper currency owes its origins to the dynasties of Middle Age China. In the Tang dynasty (618–907), the ruling class found it burdensome and potentially dangerous to transport heavy copper coinage to and from distant lands, so merchants began to be paid with paper certificates, called “flying cash” because it had a tendency to blow away. The notes were backed up by hard metal currency held in the capital. The Song dynasty that followed issued paper money with bank seals, officially embracing paper money as a means of exchange. The concept is thought to have traveled westward with the Mongols and, by 1661, European nations were also printing paper currency. The Dutch Guilder The Dutch guilder became the official currency of the Netherlands (or Holland) in 1680. It was replaced by the euro in 2002. The original guilder was a silver coin featuring the Greek god Athena, a good example of the lasting effect that Greco-Roman culture had on the newer nations of Europe. The first paper guilders were issued in 1814 and became an important global currency as Dutch traders and colonists sailed around the world. The notes shown here were designed in the 1980s and demonstrate the variety and graphic complexity that modern nations used to help express their identity and to protect their currency from counterfeiting. Contemporary Currencies When the euro replaced the currencies of numerous European nations in 2002, it instantly became an important global medium of exchange. The U.S. dollar, the British pound, and the Japanese yen are some of the other most prominent currencies regularly used today. Even in today’s global economy, there are still 182 different currencies recognized by the United Nations. Travelers often exchange some of their own money for that used by the country they are visiting. Credit Cards Credit cards are one of the most common forms of payment today. Individuals and companies using cards are able to make or receive payments without exchanging actual money. The cards link transaction amounts to certain identities. Individuals and businesses are responsible for covering their charges while the merchants receive payment from the cardholders' banks. The banks who issue credit cards calculate exchange rates when a transaction involves currencies from different nations. Often, credit card users pay fees and incur interest when they let purchases accumulate or when they borrow money “against” their card. The earliest forms of credit cards were introduced in the early 1900s as a way to secure customer loyalty. These cards were only accepted at the businesses that issued them. It wasn't until 1950 that the Diners Club Card became the first modern, multi-use "charge card." Virtual Money Nowadays, many transactions can be completed through the Internet by portable devices like phones and tablet computers. Merchants can run a customer's credit card through a reader like the "Square" shown here and instantly process a payment. That same customer might make a number of charges online and in-person, receive a paperless bill from the credit card company, and process payment online. Hundreds, thousands, or even millions of dollars might be spent without a single exchange of coin.

A Curious Case: African Agrarianism By David Baker, adapted by Newsela Due to the “late” start of agriculture in Central and South Africa below the Sahara and Sahel, we only see the first glimmer of agrarian civilizations beginning to emerge in the region from 1000 to 1500 CE, before their development was interrupted by the unification of the world zones. The Curious Case of Africa Compared to other world regions like the Fertile Crescent, Africa below the Sahara and Sahel adopted agriculture relatively “late” in human history. The Fertile Crescent began farming around 9000 BCE, West Africa independently developed agriculture around 3000 BCE, and East Africa enjoyed the transmission of knowledge from both hubs. Central and South Africa, on the other hand, only developed agriculture after the Bantu farmers migrated across the region between 1000 BCE and 500 CE. In many ways it is not surprising that Central and South Africa should have been relatively late in their transition from foraging to agriculture, since human ancestors evolved over millions of years to forage in African ecosystems, and were particularly well suited to their coexistence with nature. The late start of agriculture in Central and South Africa below the Sahara and Sahel, however, did affect the development of agrarian civilizations. Most early Central and South African states started up between 1000 and 1500 CE, and did not cover as much territory as the East and West African states. Additionally, huge swathes of Africa did not develop states at all from 1000 to 1500, but stayed in the phase of smaller agrarian communities that precedes agrarian civilizations everywhere. It is an open question whether or not Central and South Africa would have produced large states if they had been given a bit more time to develop before the world zones collided around 1500. As it was, the “early agrarian” phase usually takes several thou-sand years to produce states. The Fertile Crescent took at least 4,000 years to produce states after they first started farming. West Africa took about 3,000 years to produce the first major states and kingdoms. Since farming only really took hold in Central and South Africa around 1000 BCE to 500 CE, they did not have as much time. In order for an early agrarian community to produce states, the farmers there need to produce a lot more food than they need to survive. This supports densely populated settlements, towns, and cities. It supports a “division of labor” which allows some people to work in positions without farming for themselves – bureaucrats, scribes, rulers, priests, architects, blacksmiths, professional soldiers, and so on. The majority of Central and South Africa only had 2,000 years at the most (and in most cases considerably less) to move from the dawn of agriculture to the origin of states. That being said, some small states were already emerging in the region, further indicating that the “human experiment” has a lot of similarities even when it is conducted in different parts of the world. It is interesting to note how, after centuries of prejudiced talk about “superior” and “inferior” civilizations, it may all be a simple coincidence of timing – depending on when the healthy foraging peoples of a region are sucked into the much harsher and unhealthier life of early farming. From there the tumbling snowball effect of rising human complexity takes time. This was time that the agrarian civilizations of Central and South Africa simply did not have in abundance. Central and South African States From 1000 to 1500, long after the ancient Greek and Roman civilizations had faded from history and much of while the world dwelt in long-established medieval societies, the first states began appearing in Central and South Africa. In a few places, small agrarian communities formed into slightly larger tribal kingdoms of a few thousand people. Then, through warfare and intermarriage, these kingdoms transformed into the handful of larger states that existed in Central and South Africa before the arrival of the Europeans around 1500. In the eleventh century, Mapungubwe arose in southern Africa. Believed to be a Bantu settlement, it was a very small community of only a few thousand people, but was remarkable for its clustering of a dense population within its stone walls. Aside from farming and herding, Mapungubwe dealt in the gold and ivory trade. Surrounded by much smaller agricultural communities for miles in any direction, at the time Mapungubwe would have looked quite remarkable. These people migrated north and set up an even more impressive kingdom, the Kingdom of Zimbabwe. Its capital, Great Zimbabwe, had tall stone buildings and housed three to four times as many people, upward to 20,000. By the 1200s, Great Zimbabwe had become a center for long-distance trade, exporting and importing goods to lands as far away as Arabia and China. In turn, this kingdom was absorbed by the Mutapa Empire, which arose in the 1400s. How-ever, even at its widest extent, Mutapa was considerably smaller than the states of West Africa. And a few decades later, Portuguese traders made contact, started expanding their political influence there, and began the process that would sweep the region into the wider story of the unification of the world zones. To the northwest, in what today is the Democratic Republic of Congo, the Luba and Lunda kingdoms formed from much earlier agrarian communities. There had been fishing communities in the region since 400 CE, and they had firmly adopted farming around 900 at the latest. But states take time to form after the adoption of agriculture, in some cases many thousands of years later. In contrast to the Fertile Crescent, Luba and Lunda took only a few centuries. The Luba villages were united in the 1300s and 1400s and became a concrete state under a single king in the late 1500s. Similarly, the neighboring Lunda raised up a unified state made up of agrarian clans by 1600. Both kingdoms became trading hubs with a fairly sizable amount of territory. Due to the remoteness of their location in the middle of the southern continent, they did not fully succumb to colonialism and the unification of the world zones until the 1800s. To the west, on the African coast, several small kingdoms had arisen in the 1300s and were taking part in coastal trade. By 1380 or 1390 (there were no written records, so it is unclear) these were united into the Kingdom of Kongo. The capital of Kongo had started out as a large settlement and evolved into a densely populated city-state of many thousands of people. It ruled over a countryside with a comparatively thin population of farms and tiny agricultural villages. Kongo was a considerably wealthy king-dom with a powerful military. They traded mostly in natural resources. They quickly expanded east and began a slave trade of prisoners of war. However, Kongo formed only a century before the Portuguese arrived in the 1480s and began rapidly expanding their political influence, converting people to Christianity, buying slaves for the Americas, and initiating centuries of military interference. All of these agrarian civilizations had a division of labor, an established ruling elite, towns of thousands, military capabilities, and skills at architecture, sculpture, and iron manufacturing. Other agrarian communities in Central and South Africa had coalesced into loose alliances of villages, headed by chiefs and kings, or trade posts that expanded their influence into their hinterlands. However, it was Zimbabwe-Mutapa, Luba, Lunda, and Kongo that managed to form the largest and most complex states, with a concrete and strong authority over their subjects, prior to 1500. A number of independent states, kingdoms, and empires were to rise after 1500, but their stories become increasingly interwoven with that of European exploration and colonialism. Gold rhino found at Mapungubwe Cultural Landscape, South Africa Lessons in Collective Learning If agriculture had arisen in Central and South Africa a few millennia earlier like it did in West and East Africa, it seems likely that these small states would have grown even larger, perhaps even forming mas-sive empires. As it was, the “late” start of agriculture in the region meant that Central and South Africa’s independent story was interrupted by the larger story that was driving the world closer and closer together – sometimes with painful results. In many ways, these agrarian civilizations were “strangled in the cradle” by the expansionism of older human societies. Since the emergence of our species approximately 200,000 years ago, collective learning has steadily increased from generation to generation. We refined our foraging skills in Africa and 64,000 years ago began adapting to new and strange environments all over the world. Taken globally, human culture and society have increased in complexity by leaps and bounds. Yet if we look more closely at recent human history, there seems to be some inequality in the levels of complexity and collective learning that permitted one human group to exploit another. These inequalities between human groups find their source in different starting points of the origin of agriculture and the beginning of agrarian civilizations. Many regions of the world, like the Fertile Crescent, were “trapped” into lives of farm-ing many thousands of years ago, despite the fact that foraging was easier and healthier. Regions like Central and South Africa enjoyed the benefits of foraging for a lot longer, and escaped the less healthy life of early farming until between 1000 BCE and 500 CE. While this “late start” was a definite advantage in terms of healthy living and a less strenuous lifestyle for many thousands of years, it turned into a curse when African communities encountered explorers and armies from civilizations that were trapped into agriculture many thousands of years ago. On the long view of history over the past 10,000 years, Central and South Africa was in many ways a much nicer place to live than many other regions of the world. It escaped farming for longer, and after 1000 BCE most regions still escaped the oppressive hierarchies that characterize most agrarian civilizations and empires. On the other hand, when reading the past 500 years of Central and South African history, it is difficult not to be depressed or pessimistic. However, contrasted to 200,000 years of human existence, this painful era looks rather brief. What will determine whether this period of history is a beginning of a long downturn or a mere transitional phase into a global system of rapidly increasing collective learning is how Africa adapts, copes, and is treated by its neighbors during the twenty-first century and beyond. Map showing pre-colonial cultures of Africa (spanning roughly 500 BCE to 1500 CE). [Sources and attributions]

The Lion of the Sea: Ahmad Ibn Majid By Bridgette Byrd O’Connor Being a great sailor requires a lot of knowledge, and the greatest among them relied heavily on the collective learning that made crossing the vast Indian Ocean possible. Oceans of knowledge You’ve read the histories of famous thirteenth- and fourteenth-century explorers like Ibn Battuta and Zheng He. The tales of their journeys are incredible. But have you ever wondered how—hundreds of years ago—they managed to travel across thousands of miles and trade with the people they had just met? For example, why was Ibn Battuta welcomed in places like East Africa, the Arabian Peninsula, India, and China, even though he was a stranger from far away? How did Zheng He manage to safely get his massive ships across the perilous Indian Ocean multiple times? What skills, knowledge, and experience must they have had? The two answers I’m going to share are very different, yet equally accurate: First, the spread of a common belief system; and second, collective learning. A great way to understand both of these explanations is to take a close look at the life of one fifteenth-century Omani navigator. His name was Ahmad Ibn Mājid. Map of the Indian Ocean showing the route of the fifteenth-century Chinese explorer Zheng He. We don’t know specific routes taken by Ahmad Ibn Mājid but we do know that he carefully described tides, monsoon winds, and currents near various port cities such as Muscat, Riyadh, and Hormuz in the Indian Ocean and others on the coast of East Africa and Indonesia. By BHP, CC BY-NC 4.0. Background: A sailor’s education Ahmad Ibn Mājid was born in Julfar, a port city of the Omani Empire, c. 1432 CE. For context, this was about the time Zheng He’s ships were sailing around the Indian Ocean. Ibn Mājid’s father and grandfather were skilled sailors who owned several merchant ships. But before Ibn Mājid could journey out to sea, he had to complete his religious studies. This included memorizing the Qur’an, the holy book of Islam—a requirement for all educated Muslims. His studies also included geography, mathematics, astronomy, languages—and of course, sailing. It might be obvious why an aspiring sailor had to study sailing, but what do all those other subjects have to do with it? Fifteenth-century sailors had a limited number of navigational instruments. Sailors and traders in the Indian Ocean probably used a compass if they had access to one. That important Chinese invention goes back at least as far as the tenth century, when it was first mentioned in a text. By Ibn Mājid’s time, the compass had made its way along trade routes from China to India and the Arab world. But it could be difficult to use at sea. Therefore, geography was an essential subject for anyone wishing to sail across the Indian Ocean to cities thousands of miles away. Sidereal or compass rose shows the directions of north, south, east, and west including points in between, which was used to help sailors navigate to different locations. By BHP and Peter Quatch, CC BY-NC 4. Astronomy was also important for sailors, because the stars and planets were useful markers for finding your way. Arab sailors relied on a tool called an astrolabe, first used by Ancient Greeks, that could determine the altitudes of stars and planets. Arab sailors made improvements to the astrolabe so it could be used to figure out a ship’s latitude (latitude is a way of describing location in terms of north and south). They did this by calculating the angle of the Sun’s altitude at a given time of day. Latitude at sea could also be found using a kamal—a piece of wood fastened to a cord or string with a series of knots in it. Sailors used this instrument to measure latitude using the polestar, or the brightest star nearest to Earth at a given time. Understanding how to determine latitude required knowledge of both mathematics and astronomy. But to be a successful merchant and sailor in the Indian Ocean, you really needed knowledge of languages and cultures. If you wanted to trade with the many peoples around the region, knowing their beliefs and speaking their languages were key skills. Fortunately, lots of people in the region shared a language, Arabic, and a faith—Islam. This was how Ibn Battuta felt welcome in ports across the Indian Ocean. In fact, he even worked as a judge in a variety of places. Having a common language and religious beliefs united communities from Africa across the Arabian Peninsula to India and Indonesia. The development of a group of skilled sailors was important for faith as well as trade. Indian Ocean sailors transported more than goods across the seas; they also moved people. At least once in their lifetimes, Muslims were required to perform the hajj, or pilgrimage, to Mecca (in what is now Saudi Arabia). As Islam spread throughout the region, pilgrims from Africa to Indonesia traveled across the Indian Ocean making their hajj to Mecca. The sailors’ knowledge of mathematics and geography helped the pilgrims on the journey as well. Muslims were required to pray in the direction of Mecca five times a day. A good navigator was necessary to point the pilgrims in the correct direction of the holy city at prayer time. An astrolabe that was used to determine one’s position at sea. By BHP and Peter Quatch, CC BY-NC 4.0 An Arab sailor using a kamal, another instrument used to determine latitude at sea. By BHP and Peter Quatch, CC BY- This image depicts a dhow, the dominant type of ship used in the Indian Ocean during Ibn Mājid’s time. By BHP and Peter Quatch, CC BY-NC 4.0 Collective learning on the seas Ibn Mājid earned a reputation as a master navigator, or mu’allim in Arabic. His seafaring skills were known throughout the Indian Ocean, earning him the nickname “Lion of the Sea.” He gained much of his knowledge from the lessons his father and grandfather taught him at sea. But he also learned from centuries of oral and written tradition. Navigational information was collected and passed down across generations in the form of long poems that were memorized, just as the Qur’an was committed to memory. However, Ibn Mājid’s contribution to collective learning1^11start superscript, 1, end superscript extended beyond teaching his children these lessons. He wrote several books on navigation. Some were in the form of poems that helped document the oral tradition. Others were more like an encyclopedia of navigation skills. His most famous was the encyclopedia Kitāb al-fawā’id fī ușūl wa-l-qawā’id (Arabic for Book of Benefits in the Principles of Navigation). This work provided information about all aspects of sailing in the Indian Ocean and Red Sea. Topics included tides, monsoon winds, currents, and distances between ports. It also covered how to determine latitude using the polestar; reefs and other obstacles the sailor might encounter; the movement of the Sun and Moon; and much more. In compiling knowledge from those who came before him along with his own expert advice, Ibn Mājid made a significant contribution to collective learning. Yet we shouldn’t forget that Ibn Mājid’s writings were the product of centuries of collective learning that took place in this region. Think about what you’ve learned so far about the spread of goods and ideas. A lot of what we’ve talked about—the compass, astrolabe, shipbuilding techniques, as well as Islam and the Arabic language—traveled along the same trade routes as spices and other goods. These ideas made the Indian Ocean a large community of knowledge. Toward the end of Ibn Mājid’s life, that community changed dramatically. In 1498, the Portuguese sailor Vasco da Gama entered the Indian Ocean after sailing around the southern tip of Africa. But the Portuguese sailors at the time were not as skilled as the people who lived around the Indian Ocean. While Ibn Mājid doesn’t write about meeting the Portuguese, he does document their lack of knowledge on the seas. “We have ... the measurement of stellar altitudes, but they have not. They cannot understand the way we navigate, but we can understand the way they do; we can use their system and sail in their ships. For the Indian Ocean is connected to the All-Encompassing Ocean, and we possess scientific books ... they have ... only the compass and dead reckoning ... We can easily sail in their ships and upon their sea, so they have great respect for us and look up to us. They admit we have a better knowledge of the sea and navigation and the wisdom of the stars.” In fact, Vasco da Gama had to enlist the help of an Indian Ocean sailor to make the journey from Malindi (Kenya) to India. Some historians argue that it was Ibn Mājid who helped da Gama reach India, while other historians disagree. Ibn Mājid was probably not the one piloting da Gama’s ship. But da Gama certainly wouldn’t have reached his destination without the collective learning that took place in the Indian Ocean and the contributions of Ibn Mājid and countless others. Page from Ahmad Ibn Mājid’s encyclopedic work, Kitāb al-fawā’id fī ușūl wa-l-qawā’id (Arabic for Book of Benefits in the Principles of Navigation). By Library of Congress, public domain. [Notes] Author bio Bridgette Byrd O’Connor holds a DPhil in history from the University of Oxford and has taught the Big History Project and World History Project courses and AP US government and politics for the past 10 years at the high school level. She currently writes articles and activities for WHP and BHP. In addition, she has been a freelance writer and editor for the Crash Course World History and US History curricula. [Sources and attributions]

China: The First Great Divergence By David Baker, Adapted By Newsela The story of Medieval China is an example of the power of collective learning to produce rapid advances in human complexity. The two “great divergences” Historians sometimes refer to the Industrial Revolution as the “Great Divergence” where suddenly the energy bonanza of industry catapulted Europe and North America ahead of most of the rest of the world for much of the nineteenth century and the early twentieth century. The increase of population numbers and the rapid increase of connectivity between world zones certainly gave the West an advantage in collective learning and the harnessing of energy flows for quite some time. It was a cultural “Cambrian explosion” where human complexity suddenly burst into many diverse and intricate new forms. What is often forgotten is this was only the “second Great Divergence” of the Common Era (CE). Thanks to collective learning, the “first Great Divergence” of the Common Era happened in China in the tenth and eleventh centuries, giving China a technological edge that lasted several centuries. Collective learning has two main drivers: population numbers and connectivity. High population numbers are important because they give you a bigger group of potential innovators. The more people you have, the more likely it is that someone is going to innovate on existing knowledge and pass their new knowledge on to the next generation. Connectivity is also important because you need to increase the exchange of in- formation between those potential innovators. If people exchange ideas, it increases the odds that someone is going to “connect the dots” and come up with a breakthrough idea, as well as transmit that idea across a kingdom, a region, or even the world. The rapid growth of the Chinese population In the centuries before the Common Era (BCE), China had a lot of advantages in terms of collective learning already. They were already using efficient agricultural methods that would not be used in Europe for many centuries. They used heavy iron plows, seed drills, horse harnesses around the torso rather than the neck allowing them to carry more, careful planting methods, and advanced weeding techniques. This resulted in a larger population of potential innovators. This translated into the Chinese being the first inventors of a lot of technologies. But at this time, the majority of the Chinese population lived in the north, around the Yellow River valley, where the dominant crops were millet and wheat – not rice. Rice has an advantage over grain products because it can support more people in a given land area. After the harvest, transforming grain into bread products is labor in- tensive. Preparing rice for human diets is less so. You can also get a lot of rice out of a small plot of land. Per hectare, traditional varieties of rice support 5.63 people compared to wheat supporting 3.67 people. Rice was already present in Southeast Asia for several thousand years, and had moved into south China. Meanwhile, the bulk of the Chinese population in the north continued to farm grains. China is frequently associated with dense populations and rice, but the largest and densest area of China thrived on a grain agriculture until relatively “later” in Chinese history. In southern China before 200 CE, the yield from wet rice farming was not as high as it could have been. Rice is most efficiently grown in water, but because the Chinese be- fore 200 did not use terracing and rice paddy systems, but grew rice beside streams and in small irrigated plots, the harvest of rice was smaller. “Dry rice farming,” mean- while, was not much more efficient than wheat. This is the reason why northern China held the bulk of the population despite the long history of wet rice farming to the south. After 200, south China began to increasingly use terracing and rice paddies. This allowed higher crop yields, supporting a larger population. At the fall of the Han dynasty in 220, foreign attacks forced more Chinese south to the Yangtze River basin. Intensification of rice farming and the growth of migration to the south continued for several centuries. Gradually, this raised the population. Collective learning got another boost under the Song dynasty (960-1276). They enacted a set of policies that vastly increased the population during their reign. They introduced better strains of rice into China from Vietnam. They appointed farming experts to spread knowledge of new farming techniques, tools, fertilizers, and irrigation methods. They gave tax breaks to people who were beginning to farm unoccupied land, and gave low-interest loans to them to buy new tools and crops. The result was a rapid increase in the size of the Chinese population. This was good news for collective learning. By 800, the population of China was around 50 million to 60 million and did not far exceed that number prior to the tenth century. By 1100, the population had grown to an estimated 110 million to 120 million, approximately doubling the number of potential innovators. Meanwhile, China had woodblock printing, allowing for information to be transmitted more reliably to a greater number of innovators. As a result, collective learning leaped forward. Four centuries of rapid innovation This counts as the “first Great Divergence” between East and West in the Common Era. China had a greater number of potential innovators and it is no coincidence the Song dynasty was one of the most technologically advanced and industrially productive societies in pre-modern history. Some scholars say that the Song dynasty came close to having a Modern Revolution of their own. Farming techniques improved: use of manure became more frequent, new strains of seed were spliced and developed, hydraulic and irrigation techniques improved, and farms shifted to crop specialization; all of which are hallmarks of farming in modernity. Coal was used to manufacture iron and iron production increased from 19,000 metric tons per year under the Tang dynasty (618-907) to 113,000 metric tons under the Song dynasty (960-1276); changes that are very similar to those seen in the Indus- trial Revolution. The minting of coin currency increased by 4,500 percent under the Song dynasty and Song China was the first society to use banknotes. The Song dy- nasty was also the first to invent and harness the power of gunpowder. The Song Chinese mechanized textile production almost to a degree that would be seen in Britain centuries later. They invented the magnetic compass to open up greater exploration of the seas and the wider world. They made advances in mathematics, geometry, and cartography. They invented movable type printing four centuries before Gutenberg did in Europe, further increasing the connectivity between potential innovators. All told, China from 900 to 1300 made tremendous advances that rendered it one of the most technologically advanced and wealthiest countries in the world. A Yuan dynasty (1271–1368) printing plate and banknote. Wo divergences compared The “second Great Divergence” of the Industrial Revolution gave Europe and North America a lead that has lasted a couple of centuries. Some scholars date the point where the West surpassed the East in 1850, others 1800, and a few scholars even as early as 1750, when the Industrial Revolution was first stirring in Britain. However, it would appear that the “first Great Divergence” of the Common Era gave China a mas- sive lead in collective learning and technology that lasted from about 1000 to 1700, or even later. That divergence lasted several centuries before the West overtook it. Now, after 200 to 250 years of the West being in the lead, China is rapidly catching up to it in terms of various hallmarks of modernity, technology, and production. The rapid advance of Medieval China ahead of the West highlights some of the main drivers of collective learning, one of the most important being the number of potential innovators increasing the odds of a breakthrough. It underlines the fact that now, in a united global system of more than 7 billion people, we stand a high probability of an even more rapid pace of collective learning – and astounding breakthroughs in science and technology seem to happen every year. Chinese iron workers smelting iron ore to make pig iron and wrought iron in 16th century. On the other hand, the tremendous advance of collective learning in Medieval China highlights a puzzling question: why did the Industrial Revolution not occur there several centuries before it did in Britain? Were the societal conditions not quite right after the fall of the Song Dynasty? Was China not well connected enough with the other world zones? Or, were a few crucial inventions required to kick-start the Industrial Revolution just not thought of, by pure chance, by the vast numbers of potential innovators in China? Having more brains humming away at a problem can increase the odds of a breakthrough, but it doesn’t guarantee one. As it was, China continued to have a lead in human complexity for quite some time, and its population continued to grow. Crops from the Americas became widespread in China in the 1600s, and land ill-suited for farming rice was given over to yams, maize, potatoes, and American beans. Yet in the eighteenth and nineteenth centuries, when the European population was generally growing thanks to a rapid chain of break- throughs, China entered a period of famines and population strain. The “second Great Divergence” had begun. As of now, there are many potential answers as to why the Industrial Revolution occurred when and where it did, sending humanity on new path toward the Anthropocene and unprecedented heights of complexity in the Universe. A better understanding of that mystery might help us better understand where collective learning may take us next. [Sources and attributions]

Muslim Traveling Judge A 1605 painting of a young holy man © Stapleton Collection/CORBIS By Cynthia Stokes Brown The account of the travels of the Muslim legal scholar Ibn Battuta in the first half of the 14th century reveals the wide scope of the Muslim world at that time. The Abode of Islam During the life of Ibn Battuta (sometimes spelled Battutah), Islamic civilization stretched from the Atlantic coast of West Africa across northern Africa, the Middle East, and India to Southeast Asia. This constituted the Dar al-Islam, or “Abode of Islam.” In addition, there were important communities of Muslims in cities and towns beyond the frontiers of Dar al-Islam. People in the whole “umma,” or community of people believing in one god and his sacred law (“shari’a”), shared doctrinal beliefs, religious rituals, moral values, and everyday manners. In the early 1300s this community was expanding dramatically. Background Ibn Battuta was born in Tangier, part of modern-day Morocco, on February 25, 1304. This port city on the coast of the Atlantic Ocean lies 45 miles west of the Mediterranean Sea, close to the western side of the Strait of Gibraltar — where Africa and Europe nearly collide. The men in Ibn Battuta’s family were legal scholars and he was raised with a focus on education; however, there was no “madrasa,” or college of higher learning, in Tangier. Thus, Ibn Battuta’s urge to travel was spurred by interest in finding the best teachers and the best libraries, which were then in Alexandria, Cairo, and Damascus. He also wanted to make the pilgrimage to Mecca, called the “hajj,” as soon as possible, out of eagerness and devotion to his faith. An interactive display at the Ibn Battuta Mall in Dubai, Dubai Construction Update, Imre Solt On June 14, 1325, at the age of 21, Ibn Battuta rode out of Tangier on a donkey, the start of his journey to Mecca. Unlike the young Marco Polo, he was quite alone, as illustrated by this passage from The Travels of Ibn Battuta, his detailed account of his wanderings: I set out alone, having neither fellow-traveler in whose companionship I might find cheer, nor caravan whose party I might join, but swayed by an overmastering impulse within me and a desire long-cherished in my bosom to visit these illustrious sanctuaries. So I braced my resolution to quit all my dear ones, female and male, and forsook my home as birds forsake their nests. My parents being yet in the bonds of life, it weighed sorely upon me to part from them, and both they and I were afflicted with sorrow at this separation.— from The Travels of Ibn Battutah I set out alone, having neither fellow-traveler in whose companionship I might find cheer, nor caravan whose party I might join, but swayed by an overmastering impulse within me and a desire long-cherished in my bosom to visit these illustrious sanctuaries. So I braced my resolution to quit all my dear ones, female and male, and forsook my home as birds forsake their nests. My parents being yet in the bonds of life, it weighed sorely upon me to part from them, and both they and I were afflicted with sorrow at this separation. — from The Travels of Ibn Battutah Travels Ibn Battuta’s solitude did not last long, according to his chronicles. The governor of one city gave him alms of gold and woolen cloth, as almsgiving was considered a pillar of Islam. Ibn Battuta stayed at madrasas and at Sufi hospices as he made his way to Tunis. By the time he left Tunis he was serving as a paid judge, a qadi, of a caravan of pilgrims who needed their disputes settled by a well-educated man. Alexandria and Damascus were two highlights on the part of the trip that followed. Ibn Battuta entered Mecca in mid-October 1326, a year and four months after leaving home. He stayed a month, taking part in all the ritual experiences and talking with diverse people from every Islamic land. While his writings don’t provide much detail about what this experience meant to him, after it was over he set out for Baghdad instead of returning home. He traveled in a camel caravan of returning pilgrims, and this is when his real globetrotting began. Ibn Battuta led a complete life while traveling. He studied and prayed; he practiced his legal profession; he had astonishing outdoor adventures; he married at least 10 times and left children growing up all over Afro-Eurasia. A few examples of these activities provide a good picture of his life’s journey. In Alexandria, Ibn Battuta spent three days as a guest of a locally venerated Sufi ascetic by the name of Burhan al-Din the Lame. This holy man saw that Ibn Battuta had a passion for travel. He suggested that Ibn Battuta visit three other fellow Sufis, two in India and one in China. Of the encounter with Buurhan al-Din, Ibn Battuta wrote in his Travels, “I was amazed at his [Burhan al-Din’s] prediction, and the idea of going to these countries having been cast into my mind, my wanderings never ceased until I had met these three that he named and conveyed his greeting to them.” Ibn Battuta visited another saint who lived a quiet life of devotion in a town near Alexandria. It was summer and Ibn Battuta slept on the roof of the man’s cell. There he had a dream of a large bird that carried him far eastward and left him there. The saint interpreted this to mean that Ibn Battuta would travel to India and stay there for a long time, echoing what Burhan al-Din had said. Caravan going to Mecca, from The Maqamat by Al-Hariri © The Gallery Collection/CORBIS In Damascus, Ibn Battuta boarded in one of the three madrasas. During his 24-day stay he settled down into some formal studies. Damascus had the largest concentration of famous theologians and jurists in the Arab-speaking world. They taught by reading and commenting on a classical book, then testing their students’ knowledge of it and issuing certificates to those who passed their tests. Ibn Battuta then fulfilled the prophesies of the various seers he’d met by traveling to India via Afghanistan, where he had to cross the Hindu Kush Mountains at one of several high passes. His group crossed at the 13,000-foot (4,000-meter) Khawak Pass. “We crossed the mountains,” Ibn Battuta re-called in Travels, “setting out about the end of the night and traveling all day long until sunset. We kept spreading felt clothes in front of the camels for them to tread on, so that they would not sink in the snow.” Upon arriving in Delhi, Ibn Battuta sought an official career from the Muslim king of India, Muhammad Tughluq. The king of India made a practice of appointing foreigners as ministers and judges. As Ibn Battuta traveled to the court in Delhi, 82 Hindu bandits attacked his group of 22; Ibn Battuta and his men drove them off, killing 13 of the thieves. King Tughluq appointed him judge of Delhi, but since Ibn Battuta did not speak Persian, the language of the court, two scholars were appointed to do the work of hearing cases. After eight years, Ibn Battuta was eager to escape the political intrigue. The king agreed to send him as an ambassador to China, and made him responsible for taking shiploads of goods to the Yuan emperor, in return for the emperor’s previous gifts of 100 slaves and cartloads of cloth and swords. Ibn Battuta was set to sail from Calcutta with one large ship holding the goods for the Chinese emperor and a smaller ship filled with his personal entourage. Everything and everybody was loaded for departure, but Ibn Battuta spent the last day in the city attending Friday prayers. That evening a storm blew in, and the large ship with the presents ran aground and sank. The smaller one, with Ibn Battuta’s servants, concubines, friends, and personal belongings, took to sea to escape the storm. Reduced to his prayer rug and the clothes on his back, Ibn Battuta could only hope to catch up with the ship carrying his group. Thus Ibn Battuta’s travels continued, with narrow escapes and dramatically varying fortunes. Eventually he learned that his ship had been seized by a non-Muslim ruler in Sumatra. He decided to go to China anyway, but stopped on the way at the Maldives, an island group 400 miles southwest off the coast of India. In the Maldives, Ibn Battuta enjoyed the company of women even more than usual. Usually, he married one at a time and divorced her when he left on further travels. He often had concubines, too, purchased or given as gifts. In the Maldives he married four women on one island, the legal limit under Muslim law. As he wrote in his Travels: It is easy to marry in these islands because of the smallness of the dowries and the pleasures of society which the women offer... When the ships put in, the crew marry; when they intend to leave they divorce their wives. This is a kind of temporary marriage. The women of these islands never leave their country. From there, Ibn Battuta continued on to China. Battuta’s narrative about China occupies less than 6 percent of his whole story. It is so sketchy and confusing that some scholars doubt that he even went to China and believe he merely fabricated this part of his account. He claims to have gone as far north as Beijing, but his description of that is even vaguer than the rest, so perhaps he only got as far north as Zaitun, now Quanzhou. In any case, he admits in the Travels that in China he was unable to understand or accept much of what he saw; it was not part of his familiar Dar al-Islam: China was beautiful, but it did not please me. On the contrary, I was greatly troubled thinking about the way paganism dominated this country. Whenever I went out of my lodging, I saw many blameworthy things. That disturbed me so much that I stayed indoors most of the time and only went out when necessary. During my stay in China, whenever I saw any Muslims I always felt as though I were meeting my own family and close kinsmen. The travels of Ibn  Battuta. Click here for a larger version. Download PDF. His writing and his last years Ibn Battuta returned home in 1349 to Tangier, where he visited the grave of his mother, who had been carried off by the Black Death (plague) only a few months before his return. (During his return, he learned in Damascus that his father had died 15 years earlier.) Ibn Battuta stayed in Tangier only a few days before leaving to visit North Africa, Spain, and West Africa (Mali). He returned from that trip in 1354 to Fez, Morocco, where the local sultan commissioned a young literary scholar to record Ibn Battuta’s experiences. The scholar had to compose the whole story into literary form, using a type of Arabic literature called a rihla, indicating a journey in search of divine knowledge. The two men collaborated for two years, with Ibn Battuta telling his story and drafting notes about it. Ibn Battuta possessed an extraordinary memory, but he also misremembered some facts and dates. All we know about Ibn Battuta’s life after the writing of his book is that he held the office of judge in some town or other. Since he was not yet 50 when he stopped traveling, he is thought to have married again and to have had more children. He died in 1368 or 1369; the place of his death is not known, nor the location of his grave. The legacy of Ibn Battuta’s Travels Unlike the impact of the Travels of Marco Polo on the European world, the account of Battuta’s travels had only modest impact on the Muslim world before the 19th century. While copies circulated earlier, it was French and English scholars who eventually brought The Travels of Ibn Battuta the international attention it deserved. How does Ibn Battuta’s account compare with that of Marco Polo’s? Each traveler lived by his wits — they had that in common. Each took joy in discovering new experiences, and each exercised amazing perseverance and fortitude to complete extensive travels and return to their home country. Yet there were many differences. Ibn Battuta was an educated, cosmopolitan, gregarious, upper-class man who traveled within a familiar Muslim culture, meeting like-minded people wherever he went. Polo was a merchant, not formally educated, who traveled to strange, unfamiliar cultures, where he learned new ways of dressing, speaking, and behaving. Ibn Battuta told more about himself, the people he met, and the importance of the positions he held. Marco Polo, on the other had, focused on reporting accurate information about what he had observed. How fortunate we are to have accounts from two contrasting intercontinental travelers from more than 600 years ago. Timeline of Battuta’s life. Click here for a larger version. Download PDF. For Further Discussion How did Islam provide a comfortable environment for Ibn Battuta to travel in? Share your answers in the Questions Area below. [Sources and attributions]

Thank You for Algebra: Muhammad Ibn Musa al-Khwarizmi By Bennett Sherry The Muslim mathematician al-Khwarizmi built on ancient ideas and offered new approaches to mathematics that we still rely on today. Translating the heavens Is math the language of science? If it is, then we should thank Muhammad Ibn Musa al-Khwarizmi for translating it for us. Al-Khwarizmi was a scholar at the House of Wisdom in ninth-century Baghdad (see Figure 1). There, he was part of a community of scholars from across the world who translated and studied ancient manuscripts on science, math, medicine, history, philosophy, and more. But like most scholars, al-Khwarizmi did more than simply translate ancient books. He blended and improved mathematical concepts from ancient Babylonian, Greek, and Hindu scholars, revolutionizing how we do math. Al-Khwarizmi was invited to the House of Wisdom by the Abbasid caliph (ruler), al-Ma’mun. Al-Khwarizmi was a Persian man, probably born somewhere in Central Asia near today’s Uzbekistan. We don’t know a lot about his life. The sands of time have erased many of the details. Yet his teachings live on through his books. He made important contributions in geography, astronomy, geometry, and calendar systems. But his most important contributions were in mathematics. Algebra. Wow. Thanks. You shouldn’t have... Al-Khwarizmi is best known for revolutionizing algebra and arithmetic. He didn’t invent algebra, but he did improve the techniques we use to solve algebraic problems. His book, al-Kitāb al-mukhtasar fīhisāb al-jabr wal-muqābala(Arabic for The Compendious Book on Calculation by Completion and Balancing) is where we get the word “algebra” (from “al-jabr” or “balancing”). This book offered detailed instructions for solving linear and quadratic equations1^11start superscript, 1, end superscript, earning him the title “father of algebra.” Now, you might not be too excited about algebra, so you’re forgiven for not rushing to thank al-Khwarizmi. But consider this: algebra sounds complicated, but it can also help you solve some of life’s more complicated problems in a simple way. At its most basic, algebra allows us to use symbols (like x and y) in equations to find unknown numbers. It could be as simple as the linear equation x + 1 = 2 , where we can quickly figure out that x equals 1. Or it can be as complicated as Einstein’s blockbuster: “E = mc2.” Quadratic equations are essential if you want to do things like fly a plane, plot a course to Mars, or pass Algebra II. Unlike Einstein, you probably don’t need to solve problems involving the speed of light. Thankfully, al-Khwarizmi’s book also offered solutions for people who needed to figure out common, everyday problems. For example, his book explained how to use equations to split an inheritance, divide a plot of land, and find measurements for canals and buildings. While al-Khwarizmi was not the first person to understand these equations, he was the first to provide algorithms for solving them. Algorithms are sets of rules to solve a problem. They’re the basis of computing machines, so that means we wouldn’t have computers or phones without algorithms—or al-Khwarizmi. In fact, the English word “algorithm” comes from the Latinized spelling of his name, “Algorismi.” Now doesn’t al-Khwarizmi deserve some thanks? Rather than using numbers and symbols in his book on algebra (algebraic equations tend to look something like this: ax2 + bx + c = 0), al-Khwarizmi explained how to solve equations in words. This is surprising, because his second-most famous book encouraged mathematicians to adopt the Hindu numbering system. Developed in ancient India, these numerals are today called Hindu-Arabic numerals. Al-Khwarizmi popularized the Hindu-Arabic numeral system in the Islamic world, and his book is responsible for their adoption in Europe five centuries later. This numbering system made math a lot easier because it introduced the number zero and the concept of positional notation, which is basically the idea that the position of numbers determines their value. For example, consider the number 503. The five is in the third place to the left, which means it symbolizes units of a hundred. In this number, we know there are five hundreds and three ones. Why did this make math easier? Well, let’s try an experiment. Add up the cost of a video game, a pizza, and a pair of jeans. But here’s the catch: you can’t use the numbers you’re used to, only Roman numerals (I, V, X, L, C)...and you have to show your work. The cost of the game is LIX dollars, the pizza costs XV dollars, and the jeans are XXXIX dollars. Which adds up to “What the !@XV#%?” Now, imagine how much time you would have saved if you were adding 59+15+39. A lot faster, right? That’s thanks to al-Khwarizmi and the ancient Hindu numbering system he introduced to the Islamic world. Adding to human knowledge Al-Khwarizmi’s work in mathematics revolutionized or made possible other fields, including finance, optics, engineering, chemistry, astronomy, geography, and computing. Al-Khwarizmi made some of these innovations himself. He improved on Ptolemy’s famous world map, recording the latitudes and longitudes of thousands of cities. He produced new calendar and calculation systems for tracking the movement of the planets, Sun, and Moon. In 1202 CE—four hundred years after al-Khwarizmi wrote his books—the Italian mathematician Fibonacci introduced the Hindu numbering system to Italy. Within two centuries, these numerals were the standard across Europe. Isaac Newton claimed that he saw far because he stood on the shoulders of giants. But we often forget that he was only able to stand on those shoulders because he could read their words. The great Islamic scholars who lived during the Golden Age of Islam are the people that Newton had to thank for translating and improving the ancient works of Greek, Hindu, Babylonian, and Roman scholars. Their works circulated throughout the Islamic world, emerging from centers of learning like Baghdad, Cairo, Cordoba, Fez, and Basra. Carried by scholars from across Afro-Eurasia, these works were passed from student to teacher and translated into new languages. The early Islamic caliphs brought scholars from as far away as China and West Africa to Baghdad, where new ideas swirled together and added to our collective learning. [Notes] Author bio Bennett Sherry holds a PhD in history from the University of Pittsburgh and has undergraduate teaching experience in world history, human rights, and the Middle East. Bennett writes about refugees and international organizations in the twentieth century. He is one of the historians working on the OER Project courses. [Sources and attributions]

Climate and geography divide human populations Asia from space © CORBIS By Cynthia Stokes Brown For a brief period, from about 10,000 years ago to about 500 years ago, the rising seas at the end of the last ice age divided the world into four non-connected geographic zones. Isolated from one another, four groups of people developed distinct lifeways and conducted their own experiments in human culture. What are world zones? In his book Maps of Time, David Christian describes the division of the world into four world zones, which helps him analyze and explain human history. Many other historians have recognized the two largest world zones — Afro-Eurasia, which they often call the “Old World,” and the Americas, which they call the “New World.” But Christian was living in Australia, and preferred looking at the whole world. These are the four world zones that he uses: 01 - Afro-Eurasia: Africa and the Eurasian landmass, including offshore islands like Britain and Japan02 - The Americas: North, Central, and South America, plus offshore islands like the Caribbean Islands03 - Australasia: Australia and the island of Papua New Guinea, plus neighboring islands in the Pacific Ocean04 - The Pacific: Island societies such as New Zealand, Micronesia, Melanesia, Hawaii (Antarctica is not considered a world zone because until very recently no people lived there.) Bering Land Bridge National Preserve, Alaska, USA © Tim Thompson/CORBIS A world zone is simply a large region of human interaction, linked geographically, culturally, economically, and sometimes politically. It may have a hundred thousand to millions of people living in different types of communities. Each of the four world zones functioned as a separate world, not in regular contact with other zones until Europeans sailed to the Americas late in the 15th century. The world today no longer has four separate world zones — our world is increasingly global. For most of human history, humans existed only in Afro-Eurasia. Homo sapiens migrated to Australasia about 60,000–50,000 BCE and to the Americas about 20,000–15,000 BCE. Human interaction continued among these three areas until the melting at the end of the Ice Age caused sea levels to rise sufficiently to drown the land bridge between Asia and the Americas. There never was a land bridge between Australasia and Afro-Eurasia; a significant sea passage always existed, which is why the arrival of humans in Australasia seems such an achievement. But the passage between Afro-Eurasia and Australasia became wider, and harder to cross, after the seas rose. The rising of the seas occurred sometime after humans got to the Americas, creating three separate world zones. The fourth world zone, the Pacific Islands, did not emerge until humans became skilled enough at sailing to reach these islands — sometime in the past 4,000 years. Hence three of the four world zones operated from about 10,000 BCE to about 1500 CE, while the fourth functioned only from about 2000 BCE to 1500 CE. After 1500 CE, extensive travel by sea connected all of the zones and established the first global exchange network. What the four world zones reveal The rising seas cut off the four groups of humans from each other long enough for them to develop different experiments in culture and civilization, but not so long that they would develop into separate species. How amazing is that? Comparing human societies is a bit like deciding whether a glass is half full or half empty. You can notice how different human societies are from each other, or you can exclaim how similar they are to one another. World history and anthropology courses usually focus on the differences in human societies in the four world zones. Big history courses focus instead on the similarities of different human societies, even though they were completely separated from each other for quite a long period. Agrarian civilizations emerged only in the two largest world zones for very specific reasons. A closer look at the four zones demonstrates that some zones had more advantages than others. Afro-Eurasia was so much larger, with better plants for food and animals better suited for transportation, that civilization emerged there several thousand years earlier than in the Americas. This gave peoples from Afro-Eurasia a decisive edge when they arrived in the Americas and found civilizations similar to theirs in structure, but earlier in their development. The smaller two world zones were so much smaller in their habitable land mass, available resources, and population that they did not reach the density of people required for civilization in the time allowed. On the larger Pacific islands, like Hawaii and New Zealand’s North Island, agriculture emerged, and something very close to states. Would these societies have become states/civilizations if they had not been interrupted by conquest from the larger zones? We can never know. In most areas of the Australasian world zone people remained foragers until the arrival of the Europeans. Agriculture did emerge in the highlands of Papua New Guinea, but their root crops could not be stored in large quantities and villages were not easily connected. Hence, political structures beyond village life did not emerge. On the Australian mainland, widespread agriculture never developed. Soil was poor and, by chance, the available species of plants were not easy to domesticate. Still, archaeological sites show that the population was increasing in the two millennia before Europeans arrived. When you compare the four zones, it’s easy to see the advantages that people living in Afro-Eurasia had over the other regions. Its people had a head start with the earliest human habitation, the greatest geographic area, and the largest population. Afro-Eurasia also had the most varied resources and the largest networks of collective learning, which contained more — and more diverse — information than those networks existing in the smaller zones. For Further Discussion How do you think the domination of one world zone over the others has influenced the world today in terms of access to innovation and economic success? Share your ideas in the Questions Area below. [Sources and attributions]

Trade Routes Connect the Vast Continent of Afro-Eurasia A Scythian/Pazyryk horseman, c. 300 BCE,State Hermitage Museum in St. Petersburg By Craig Benjamin Beginning with early agrarian civilizations, societies started to connect into large networks of exchange, leading to levels of collective learning never seen before in human history. Making Connections Agrarian civilizations did not exist in isolation. As they grew and stretched their boundaries they joined up to form larger structures. This linking up of different civilizations was an important process because it ensured that collective learning reached further and embraced more people and greater diversity than ever before. Significant exchanges occurred in the Americas, in Australasia, and in the Pacific, but the most important exchange networks emerged in Afro-Eurasia. At this time these four zones were still so isolated from each other that humans living in one remained utterly ignorant of events in the others. In Afro-Eurasia, all agrarian civilizations were linked together into a vast interconnected network by the beginning of the Common Era. This network involved not only the trading of material goods, but also the trading of social, religious, and philosophical ideas, languages, new technologies, and disease. The most important exchange system that existed anywhere during the Common Era is known today as the Silk Roads, but significant smaller connections developed much earlier between many of the agrarian civilizations. Heicheng in China’s Inner Mongolia Autonomous Region© Asigang/Xinhua Press/Corbis Not all these connections were based on trade. Warfare is common to all agrarian civilizations, so conflict was also a powerful way of connecting civilizations. It was through warfare that the Romans eventually connected many of the peoples of Afro-Eurasia. Centuries later, Muslim armies quickly constructed a vast Islamic realm that stretched from Europe to the borders of the Tang dynasty’s empire, deep in central Asia. Although these military relationships were important in establishing connections, the most influential connections of the era were built through trade. Trade was important from the beginning. As early as 2300 BCE, civilizations in Mesopotamia, Egypt, and the Indus Valley were involved in commercial relationships. The Silk Roads enabled these early small-scale exchanges to expand dramatically, leading to even more significant changes in human history, and to intensive collective learning. The First Silk Roads Era (50 BCE–250 CE) The first major period of Silk Roads trade occurred between c. 50 BCE and 250 CE, when exchanges took place between the Chinese, Indian, Kushan, Iranian, steppe-nomadic, and Mediterranean cultures. A second significant Silk Roads era operated from about 700 to 1200 CE, connecting China, India, Southeast Asia, the Islamic realm, and the Mediterranean into a vast web based on busy overland and maritime trade. The primary function of the Silk Roads during both periods was to facilitate commercial trade, but intellectual, social, and artistic ideas were also exchanged. Historians believe that it is these nonmaterial exchanges that have been of greatest significance to world history. Large-scale exchanges became possible only after the small early agrarian civilizations were consolidated into huge and powerful empires. By the time of the first Silk Roads era just four ruling dynasties — those of the Roman, Parthian, Kushan, and Han empires — controlled much of the Eurasian landmass, from the China Sea to the Atlantic Ocean. Order and stability was established over a vast geopolitical environment, great road networks were constructed, advances were made in metallurgy and transport technology, agricultural production was intensified, and coinage appeared for the first time. By 50 BCE, conditions in Afro-Eurasia were much different than they had been before the consolidation of empires. A camel and rider from a Mughal Empire ceremonial procession,public domain Pastoral nomads (humans who form communities that live primarily from their domesticated animals like cattle, sheep, camels, or horses) were also important in these exchanges. Toward the end of the first millennium BCE, large and powerful pastoral nomadic communities appeared — the Scythians, the Xiongnu, and the Yuezhi. The ability of pastoral nomads to thrive in the harsh interior of Inner Asia helped facilitate the linking up of all the different civilizations and lifeways, as travelers depended on these people when the Silk Roads formed. It was the decision by the Han Chinese in the first century BCE to interact with their western neighbors and engage in long-distance commerce that turned small-scale regional trade into a great trans-Afro-Eurasian exchange network. This occurred around the same time that Augustus came to power in Rome following a century of civil war. In the relatively peaceful era that ensued, the demand for foreign luxury goods in Rome exploded, leading to a huge expansion of both land-based trade routes connecting the Mediterranean with East Asia, and maritime routes connecting Roman Egypt to India. The major Chinese export commodity in demand in Rome was silk, an elegant, sensual material formed by silkworms that was highly coveted by wealthy women. The Chinese carefully guarded the secret of silk, and border guards searched merchants to make sure they weren’t carrying any actual silkworms out of the country. The Romans also prized Han iron for its exceptional hardness, as well as spices from Arabia and India, such as nutmeg, cloves, cardamom, and pepper. From central Asia, India, and the Mediterranean region, the Chinese imported agricultural products (such as grapes), glassware, art objects, and horses. The Silk Roads land routes stretched from China’s capital, Chang’an (in Shaanxi Province near Xi’an), through Central Asia and on to the Mediterranean. The animal that made Silk Roads trade possible was the Bactrian camel, which was incredibly well adapted to its environment. The humps on its back contain high quantities of fat (not water) to sustain it for long distances, and its long eyelashes and sealable nostrils guard against dust in the frequent sandstorms. The two broad toes on its feet have undivided soles, a natural adaptation to walking on sand. The bulk of overland Silk Roads trade was literally carried on the backs of these extraordinary animals. Much Silk Roads trade also took place by sea, between Roman Egypt and the west coast of India. Sailors had discovered the “trade winds,” which blow reliably from the southwest in the summer, allowing heavily laden ships to sail across the Indian Ocean from the coast of Africa to India. The winds reverse in the winter so that the same ships carrying new cargo could make the return journey to Egypt. Whether by land or by sea, however, few traders ever made their way along the entire length of the Silk Roads. Typically, merchants from the major eastern and western agrarian civilizations took their goods as far as central Asia before passing them on to a series of middlemen, like the Kushans, the Sogdians, and the Parthians. During the third century CE, the Silk Roads fell into disuse as both the Chinese and Roman empires withdrew from the network. Silk Roads trade was at least partly responsible for this, because it led to the spread of disastrous epidemic diseases. Smallpox, measles, and bubonic plagues devastated the populations at either end of the routes, where people had less resistance to each other’s diseases. As a result, the population of the Roman Empire fell from perhaps 60 million to 40 million by 400 CE, while that of China may have dropped from 60 million to 45 million by 600 CE. These huge demographic losses, which happened at the same time as the decline of previously stable civilizations (the Parthian, Han, and Kushan empires all disintegrated between 220 and 250 CE, and the Roman Empire experienced a series of crises beginning in the early third century), meant that the political situation in many parts of Afro-Eurasia was no longer conducive to large-scale commercial exchange. However, with the establishment of the Islamic realm in the eighth and ninth centuries CE, and the emergence of the Tang dynasty in China at the same time, significant Silk Roads exchanges along both land and maritime routes were revived. A painting of the Qingming Festival by Zhang Zeduan© Pierre Colombel/CORBIS The Second Silk Roads Era (700–1200 CE) Both the Tang dynasty (618–907 CE) and its successor, the Song (960–1279), presided over a vibrant market economy in China, in which agricultural and manufacturing specialization, population growth, urbanization, and technological innovation encouraged high levels of trade. New financial instruments (including printed paper money) were devised to facilitate large-scale commerce. At the same time, Arab merchants — benefiting from the stable and prosperous Abbasid administration in Baghdad (750–1228 CE) — began to engage with their Chinese counterparts in lucrative commercial enterprises, leading to a revival of the Silk Roads. The trade goods exchanged across Afro-Eurasia during this second Silk Roads era, including ceramics, textiles, foods, spices, and high-value art, were impressive. But as was the case with the first era, religious exchanges were perhaps of even greater significance to world history. Even before the Tang came to power, many foreign religions had made their way into East Asia, including Christianity, Manichaeism, and Zoroastrianism. With the advent of Islam in the seventh century and the establishment of substantial Muslim merchant communities in the centuries that followed, mosques also began to appear in many Chinese cities. But of all the foreign belief systems that were accepted in China, it was Buddhism that made the most substantial inroads. Exchange Shapes Culture The Silk Roads are the supreme example of the interconnectedness of civilizations during the Era of Agrarian Civilizations. Along these often difficult routes, through some of the harshest geography on Earth, traveled merchants and adventurers, diplomats and missionaries, carrying their commodities and ideas enormous distances across the Afro-Eurasian world zone. Each category of exchange was important, and, as a result of this interaction, Afro-Eurasia has preserved a certain underlying unity, expressed in common technologies, artistic styles, cultures and religions, and even in disease and immunity patterns. Other world zones also had their early exchange networks, but none on the scale of the Silk Roads. American trade networks happened over long distances, crossing diverse geographic regions — from the Andes through Mesoamerica and up into North America. But American networks were much smaller and less varied than those of the Silk Roads, probably because the jungles of the equatorial region acted as a barrier. Because of the Silk Roads, Afro-Eurasia was much larger in population, much more technologically dynamic, and also much more interlinked through trade and exchange than the other three world zones were. This is a particularly important distinction because, when the different zones finally collided after 1492, the societies of Afro-Eurasia were quickly able to dominate the rest of the world. And that in turn explains why the modern revolution that followed was destined to be led by Afro-Eurasian peoples, not those from the Americas. For Further Discussion The Silk Roads allowed for the exchange of goods, ideas, and diseases across Afro-Eurasia. How would this be detrimental to the culture and civilizations in other world zones? Share your answer in the Questions Area below. [Sources and attributions]

Rapid Acceleration By David Christian In the final essay of a four-part series, David Christian explains how advances in communication and transportation accelerated collective learning. Postindustrial Connections We have explored some of the ways in which networks of collective learning evolve. And we’ve focused on those processes that make collective learning operate more powerfully. Now let’s explore why collective learning has taken off like a rocket since the beginning of the Industrial Revolution. This time period is sometimes called the Anthropocene, suggesting a geologic epoch in which humans have played the dominant role in shaping our biosphere. To understand how quickly the networks of collective learning have grown, consider that the current global population of 7 billion is now connected into a single network covering the entire planet. Try calculating the number of possible connections between 7 billion different people! This network is also much more diverse than any that has ever existed because it includes all the different cultures of the entire world and all the knowledge that people in each of those cultures possess. It includes all the different ideologies and religions that have spread as people have moved from continent to continent. With these moves, different materials are relocated, crops are transplanted, and goods are exchanged. By the 19th century, refrigerated steamships made it possible to sell New Zealand butter and Argentinian beef in London, Paris, and Beijing. Today, exotic plants and hardwoods make their way from the Amazon jungle to global markets; Australian aboriginal elders teach about the Dreamtime in the United States; and 10,000 nuclear scientists from 113 different countries visit the Large Hadron Collider in Switzerland to do research on particle physics — perhaps helping us to, collectively, explain unanswered questions about the Big Bang. Collective learning is now a global process fueled by the size and diversity of an entire planet. Anyone want to start compiling a list of the different things and ideas traded around the world today? The Power of a Global Network Within these vast and diverse networks, there are huge differences in connectedness, wealth, and power. Search engines have links to just about every computer in the world. If unevenness in connectedness is linked to unevenness in wealth and power, we shouldn’t be surprised to find that levels of inequality are greater than ever before. At present, the most powerful individual in the world is probably the president of the United States. The president has the power, theoretically, to launch a nuclear war that could destroy much of the biosphere in a few hours. The rulers of agrarian civilizations had nowhere near as much power. Inequalities in power are matched by inequalities in wealth. By many measures, the gap between the very poorest in the world and the very richest has widened spectacularly in the last two centuries. In 2008 almost 1 billion people lived on less than $1 a day. That is more people than the total population of the world just 500 years ago! Meanwhile, the number of fabulously wealthy has also increased, so the gap between the very rich and the very poor is much wider than ever before. We can see powerful feedback cycles everywhere, but perhaps most clearly in technologies of communication and transportation. It took Darwin three years to sail around the world. Today, you can be in Sydney one day and in New York the next. Changes in communications are even more incredible. Just over 500 years ago, the breakthrough technology in communications was printing. Instead of copying the Bible laboriously by hand, printing presses could churn out many copies a day. Printing also aided the spread of ideas such as Copernicus’s and Newton’s views on the Universe. Then, in the 19th century, there came a flood of new technologies — steamships, telegraphs, railways, and telephones — followed in the next century by planes, radios, televisions, rockets, computers, and the Internet. Today almost anyone can communicate instantly with anyone else. A complex global network: this map shows city-to-city Internet connections in 2007. Think about the impact and scale of this change. More people, more diversity, and more complex networks with greater imbalances in knowledge, wealth, and power. Collective learning has become so widespread that it has turned us humans into a species capable of transforming an entire biosphere. It is these interconnected feedback cycles — a spiral of acceleration — that explain why collective learning now seems to be operating at warp speed. Where’s it all headed? How Collective Learning Works Rule 1 - Collective learning increases when more people are connected Rule 2 - Collective learning increases when there is greater diversity within a network Rule 3 - Uneven distributions of information produce uneven distributions of power and wealthPositive feedback cycles compound the effects of these three rules, accelerating collective learning Rule 1 - Collective learning increases when more people are connected Rule 2 - Collective learning increases when there is greater diversity within a network Rule 3 - Uneven distributions of information produce uneven distributions of power and wealth Positive feedback cycles compound the effects of these three rules, accelerating collective learning For Further Discussion What are some specific examples of differences in the number of connections or diversity of connections that you see between different parts of the world? How do you explain these differences? Share your thinking in the Questions Area below.

Anthropocene Africa - Out of Every Crisis, an Opportunity By David Baker, Adapted By Newsela While Africa’s recent history has been troubled and it still faces many dire challenges in the twenty-first century, from a Big History perspective, Africa has a tremendous opportunity in the next few centuries to play a huge role in global collective learning and the next rise of complexity. For the majority of human history, sub-Saharan Africa has been at the forefront of rising complexity. Africa was the cradle of Homo sapiens, who evolved there an estimated 200,000 years ago, and began their most crucial mass migration to the rest of the world approximately 64,000 years ago. From there, Africa remained well suited for small, closely knit foraging communities for many thousands of years. Then, around 3000 BCE, West Africa gave rise to agriculture. In the past 2,000 years, sub-Saharan Africa has been host to some of the mightiest states and empires of the ancient world. In comparison, the past 500 years have been a painful time in Africa’s history, with the slave trade and colonization, as the world zones came crashing together. In the nineteenth and twentieth centuries, sub-Saharan Africa fell behind other parts of the world in industrial complexity and economic prosperity. However, the Anthropocene offers an opportunity for Africa to play a central role in the many breakthroughs in complexity to come. Population & collective learning Sub-Saharan Africa has always possessed a lot of potential for collective learning. The two main drivers of collective learning are population numbers and connectivity. You need a pool of potential innovators to dream up ideas and increase the chances of a breakthrough, and you need connectivity to share (and combine) good ideas across a society or a region. With the Bantu spread of agriculture across sub-Saharan Africa, population numbers grew immensely, nearly tripling from 7 million in 500 BCE to 20 million people in 500 CE. A larger population of potential innovators was certainly good news for collective learning, as agrarian villages transitioned to cities and states, and needed engineers, scribes, rulers, and other specialists. While the independent states of East and West Africa were at their height in the first millennium, larger settlements, confederations of villages and regions, and alliances of tribal kings began forming on the central and southern part of the continent as well. During the next thousand years, states had begun forming in every region of Africa, while agriculture became further and further entrenched. The African population continued to grow more dramatically than ever before. Lands previously devoted to sup- porting small numbers of wide-ranging forager groups were given over to farms. Populations continued to grow, reaching an estimated 100 million in 1600. This was the high point of the sub-Saharan African populations until the twentieth century. Although Africa’s population and web of collective learning was greater than ever before, the various environments of the region could not support much more than the 100 million with traditional agriculture. Mass famines became more common, as did warfare between emerging states. And the predations of the slave trade by European traders to the Americas, and by Islamic traders to Southwest Asia, continued to sap the population. As a result, the population of sub-Saharan Africa hovered between 90 million and 95 million between 1700 and 1900. It was only after the Green Revolution of the mid-twentieth century, where genetically modified crops were introduced into Africa to combat hunger, that the population grew far beyond 100 million. Famines in Africa were still common, most notably in Ethiopia in the final decades of the twentieth century, and the standard of living for most Africans remained low. However, by the year 2000, the population of sub-Saharan Africa had grown to 659 million, a jaw-dropping increase of population in the space of a century, which completely outstripped any population growth ever seen on the African continent. Only 15 years later and that population is closer to 800 million. By 2050, it has been estimated that sub-Saharan Africa will have a population of 1.5 billion. Past 2100, the most recent U.N. estimates predict that the population of Africa alone could approach 3 billion people. Combine harvester working field, Western Cape, South Africa. Population slowdown The reason for this explosive growth is that Africa’s birth rates remain quite high, whereas population growth is gradually slowing down elsewhere in the world. In the 1970s and 1980s, there were many fears that the population would continue to grow until some sort of catastrophe hit the globe. Then, in the 1990s and 2000s, it became apparent in developed regions like North America and Europe that populations were slowing down or even shrinking. Even in developing nations like India or China, population growth is slowing down and appears to be headed toward stable levels in the later twenty-first century. While there are still many dangers concerning overpopulation, this slowdown is welcome news about humanity’s future. This is not just because of the availability of birth control. The added reasons for this demographic slowdown are that when countries begin to develop industrial economies, there are many more opportunities for careers and diverse lifestyles, children are more expensive to raise and take longer to educate to high school or even university age, and so more people opt to have one or two children, or no children at all. At a stroke, industrial prosperity has become the most successful and reliable form of population control in human history. Compare this to an agricultural society, where children are less expensive to educate, can begin helping out on the farm when they are in their early teens, and who are instrumental in looking after their families when their parents and grandparents grow old. In an agricultural society, it is in your economic and social interests to have many children. The problem is that in Africa, many regions continue to be dependent on agricultural lifestyles, which sustain huge population growth rates – in impoverished regions that are already the least equipped to cope with overpopulation. It is therefore extremely important that African countries encourage the development of their economies, particularly in the industrial sector, to prompt this slowdown of population growth that appears to have taken hold elsewhere in the world. What lies ahead for Anthropocene Africa Talking about Africa’s prospects in the twenty-first century and beyond can tend to focus pessimistically on the dire challenges and many problems that Africa currently faces. However, a Big History perspective allows some observations that would be rare in the future projections of many economists and demographers. On the timescale of several centuries, an Africa with a large population of potential innovators is the furthest from a negative thing. A large continent with a diverse population of a few billion people is a great thing for collective learning and rising human complexity as we continue to unlock more technological and scientific advancements at an accelerating pace. The immediate challenge is to raise the standard of living of most Africans, create more widespread access to education and career opportunities, and to stave off population disasters by leveling off growth rates. The best way to do all those things is to help African states develop their economies. As the recent history of Europe, America, and East Asia shows: if you develop your economy, the standard of living increases, the birth rate decreases. If we do that, then a century or two from now, it is distinctly possible that a large and populous Africa will not only offer a decent quality of life to its people, but play a central role in the human web of collective learning and the glob- al economy. In that sense, sub-Saharan Africa has the chance to revive the roles played in the first millennium by the wealthy and powerful civilizations of Ghana and Aksum. The question is how to get there. The primary goals for sub-Saharan Africa in the Anthropocene are to 1) industrialize in an environmentally sustainable way and 2) lower birth rates while continuing to raise standards of living. In the development of European economies in the nineteenth century, and in Asian economies in the twentieth century, a pivotal role is played by industrialization. Indeed, those African economies that have embraced industry in recent decades have done the best. Countries like South Africa have made major strides in recent decades. Conversely, those African economies that still have a dependence on agriculture have the lowest growth rates and some of the lowest standards of living. Countries like Sierra Leone, Zimbabwe, and the Democratic Republic of Congo have learned this to their cost in recent years. It certainly does not hurt to have mineral resources or fossil fuels to sell, but not all African countries have that option either. This has benefited the peoples of Nigeria and also smaller countries like Equatorial Guinea, Gabon, and Angola. However, on the scale of decades and centuries, when these resources dry up (or when the world turns to more renewable resources) there needs to be a more permanent economy on which a country can fall back. The best hope for African economies is to continue developing their industrial and technology sectors. Graduation of teachers from rural communities in the Northern Province of Sierra Leone. When it comes to population, having a large sprawling population is no longer the major benefit that it used to be in the agrarian era. While the most populous countries in sub-Saharan Africa are Nigeria (by a long lead), Ethiopia, the Democratic Republic of Congo, and South Africa, two of those countries – Ethiopia and the Democratic Republic of Congo – are not punching their economic weight and score quite low in human development. It is no coincidence that both countries have a huge dependence on non- industrial forms of commerce, like agriculture. Meanwhile, Nigeria holds nearly 25 percent of sub-Saharan Africa’s population but gains a lot of its GDP from its many natural resources, rather than manufacturing. Also, considering the immense amount of wealth that flows through the country, it rarely trickles down to make the average income of a Nigerian equal that of the average income in the top 10 African countries. And the human development of Nigeria leaves a lot to be desired. Meanwhile, smaller countries like Gabon and Botswana have high average incomes and human development scores, and must continue to invest in manufacturing to ensure prosperity in the future. To become a prosperous economic powerhouse in the Anthropocene, you need to have both a sizable population and have them engaged in manufacturing and technology. In previous decades, East Asian countries like Japan, China, and Korea have learned this lesson to their profit. Africa holds the potential to follow in their footsteps in the next century. Automated automobile assembly line in Durban, South Africa. If sub-Saharan African economies develop and remain stable and prosperous, the greater number of opportunities in education and careers, a rising standard of living, and an incentive to have fewer children would slow down population growth and stave off catastrophe. The key to delivering Africa to a foremost role in the global network of collective learning in the twenty-first century is to develop their economies. From a Big History perspective, this will be a major issue in the next few centuries of the Anthropocene. Today, sub-Saharan Africa makes up 12 to 15 percent of the total global population. Current estimates are that by 2100, they may constitute 30 percent or higher. This is a lot of people – a lot of potential innovators – who can contribute to human collective learning in the next few centuries, bringing on whatever amazing transformations still await us. Conversely, if sub-Saharan Africa should sink into population crisis or economic disaster, the shock waves of such a catastrophe in such a large share of the world’s population would be felt around the globe. Observing the story of 13.8 billion years of rising complexity, we must not take that trend for granted. It is easy to overlook all those human societies that collapsed into ruins, those millions of species that went extinct, and those areas of the vast cosmos that remain cold and lifeless. The rise of complexity is never guaranteed. The fate of human complexity in the next few centuries may very well turn on the fate of Africa. [Sources and attributions]