The Paleozoic Era Online exhibits : Geologic time scale The Paleozoic Era The Paleozoic is bracketed by two of the most important events in the history of animal life. At its beginning, multicelled animals underwent a dramatic "explosion" in diversity, and almost all living animal phyla appeared within a few millions of years. At the other end of the Paleozoic, the largest mass extinction in history wiped out approximately 90% of all marine animal species. The causes of both these events are still not fully understood and the subject of much research and controversy. Roughly halfway in between, animals, fungi, and plants colonized the land, the insects took to the air, and the limestone shown in the photo at right was deposited near Burlington, Missouri. The Paleozoic took up over half  approximately 300 million years (542 mya to 251 mya)*  of the Phanerozoic. During the Paleozoic there were six major continental land masses; each of these consisted of different parts of the modern continents.

For instance, at the beginning of the Paleozoic, today's western coast of North America ran east-west along the equator, while Africa was at the South Pole. These Paleozoic continents experienced tremendous mountain building along their margins, and numerous incursions and retreats of shallow seas across their interiors. Large limestone outcrops, like the one pictured here, are evidence of these periodic incursions of continental seas. The Paleozoic Era is bracketed by the times of global super-continents. The era opened with the breakup of the world-continent Pannotia and closed with the formation of Pangea, as the Earth's continents came together once again. Many Paleozoic rocks are economically important. For example, much of the limestone quarried for building and industrial purposes, as well as the coal deposits of western Europe and the eastern United States, were formed during the Paleozoic. The Paleozoic is divided into six periods: the Cambrian , Ordovician , Silurian , Devonian , Carboniferous (in the U.S., this is divided into the Mississippian and Pennsylvanian Periods), and Permian . Most of these names derive from locations where rocks of these ages were first studied.

Cambria was the Latin name for Wales, and the Ordovices and Silures were two Welsh Celtic tribes. The Devonian is named for Devonshire, England. The Mississippian is named for the upper Mississippi River valley, not the state of Mississippi, which has very few rocks of this age; however, the Pennsylvanian is named for the state of Pennsylvania. The Permian was described from rocks in the region of Perm, a town in the Ural Mountains of Russia. The exception to this naming convention is the Carboniferous; its name means "coal-bearing," and this is a time when extensive coal beds were formed around the world. Life Two great animal faunas dominated the seas during the Paleozoic. The "Cambrian fauna" typified the Cambrian oceans; although members of most phyla were present during the Cambrian, the seas were dominated by trilobites, inarticulate brachiopods, monoplacophoran molluscs, hyolithids, "small shelly fossils" of uncertain systematic position, and archaeocyathids. Although all of these except the archaeocyathids survived past the Cambrian, their diversity declined after the Ordovician.

Later Paleozoic seas were dominated by crinoid and blastoid echinoderms, articulate brachiopods, graptolites, and tabulate and rugose corals. By the end of the Ordovician , life was no longer confined to the seas. Plants had begun to colonize the land, closely followed in the Silurian by invertebrates, and in the Upper Devonian by vertebrates. The early tetrapods of this time were amphibian-like animals that eventually gave rise to the reptiles and synapsids by the end of the Paleozoic. One of the earliest terrestrial tetrapod faunas known in the world is from Joggins , Nova Scotia. Land plants evolved rapidly into the vacant niches afforded them on land. By the end of the Devonian, forests of progymnosperms, such as Archaeopteris dominated the landscape. By the end of the Paleozoic, cycads, glossopterids, primitive conifers, and ferns were spreading across the landscape.

The Permian extinction, 251.4 million years ago, devastated the marine biota: tabulate and rugose corals, blastoid echinoderms, graptolites, the trilobites, and most crinoids died out. One lineage of crinoids survived, but never again would they dominate the marine environment. Paleozoic fossil localities Aldan River, Siberia : Lower Cambrian fauna from this site in Yakutia, Siberia, trace the early evolution of animals with skeletons. Burgess Shale : One of the greatest fossil finds ever made is the Burgess fauna of British Columbia. Thousands of soft-bodied animal fossils paint us a picture of Cambrian marine life. Canning Basin, Australia : A great diversity of fossil gastropods has been uncovered in the Canning Basin. Glass Mountains, Texas : Permian fossils from the Glass Mountains are of shallow, warm-water marine life. House Range, Utah : A varied array of Cambrian critters has been found in the Wheeler Shale and the Marjum Formation, both of which are exposed in the House Range.

Joggins, Nova Scotia : Carboniferous coal swamps were home to early tetrapods such as Dendrerpeton. Lake Winnipeg, Manitoba, Canada : The limestones of this region have preserved many spectactular fossils of Ordovician macroalgae. Marble Mountains, California : Olenellid trilobites are plentiful in the Latham Shale, here in the Mojave Desert. Mazon Creek, Illinois : This site has become famous for its iron concretions preserving both plants and marine invertebrates. Rhynie Chert, Scotland : This has been one of the most important sources of fossils of early land plants and terrestrial arthropods. The anatomy of specimens is preserved in three-dimensional detail. White-Inyo Mountains, California : You can visit Cambrian reefs in the mountains of eastern California. Resources Find out more about the Mesozoic paleontology and geology of North America at the Paleontology Portal's pages on the Cambrian , Ordovician , Silurian , Devonian , Carboniferous , and Permian Periods. See the Wikipedia page on the Paleozoic. Read more about the Permian-Triassic extinction on Wikipedia.

Find out more about the complex history of the formation and break-up of Pangea on Wikipedia. * Dates from the International Commission on Stratigraphy's International Stratigraphic Chart, 2008. Tony R. Fiorillo created the original page, 5/24/1994; Allen G. Collins made modifications, 11/11/1994, and broke the original page into multiple pages 11/28/1994; Ben M. Waggoner added new text, 11/11/1994 and 11/28/1994; Brian R.

Speer updated the content, 5/20/1998; Sarah Rieboldt updated the pages to reflect the Geological Society of America (GSA) 1999 Geologic Timescale, 11/2002; Dave Smith recombined the content into a single page and adapted it to the new site format, 6/29/2011; photographer of Burlington limestone unknown The Cambrian Period Online exhibits : Geologic time scale : Paleozoic Era The Cambrian Period The Cambrian Period marks an important point in the history of life on Earth; it is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the "Cambrian Explosion," because of the relatively short time over which this diversity of forms appears. It was once thought that Cambrian rocks contained the first and oldest fossil animals, but these are now found in the earlier Ediacaran (Vendian) strata. Life Almost every metazoan phylum with hard parts, and many that lack hard parts, made its first appearance in the Cambrian.

The only modern phylum with an adequate fossil record to appear after the Cambrian was the phylum Bryozoa, which is not known before the early Ordovician . A few mineralized animal fossils, including sponge spicules and probable worm tubes, are known from the Ediacaran Period immediately preceding the Cambrian. Some of the odd fossils of the biota from the Ediacaran may also have been animals representative of living phyla, although this remains a somewhat controversial topic. However, the Cambrian was nonetheless a time of great evolutionary innovation, with many major groups of organisms appearing within a span of only forty million years. Trace fossils made by animals also show increased diversity in Cambrian rocks, showing that the animals of the Cambrian were developing new ecological niches and strategies  such as active hunting, burrowing deeply into sediment, and making complex branching burrows. Finally, the Cambrian saw the appearance and/or diversification of mineralized algae of various types, such as the coralline red algae and the dasyclad green algae. This does not mean that life in the Cambrian seas would have been perfectly familiar to a modern-day SCUBA diver!

Although almost all of the living marine phyla were present, most were represented by classes that have since gone extinct or faded in importance. For example, the Brachiopoda was present, but greatest diversity was shown by inarticulate brachiopods (like the one pictured below, left). The articulate brachiopods, which would dominate the marine environment in the later Paleozoic, were still relatively rare and not especially diverse. Cambrian echinoderms were predominantly unfamiliar and strange-looking types such as early edrioasteroids, eocrinoids, and helicoplacoids. The more familiar starfish, brittle stars, and sea urchins had not yet evolved, and there is some controversy over whether crinoids (sea lilies) were present or not. Even if present, crinoids were rare in the Cambrian, although they became numerous and diverse through the later Paleozoic. And while jawless vertebrates were present in the Cambrian, it was not until the Ordovician that armored fish became common enough to leave a rich fossil record. Left: Acrothele, a fairly common inarticulate brachiopod from the the Wheeler Shale of western Utah.

Middle: Olenellus fremontii from the Latham Shale of southern California. Right: A hyolith, also from the Latham Shale. Other dominant Cambrian invertebrates with hard parts were trilobites (like the one pictured above), archaeocyathids (relatives of sponges that were restricted to the Lower Cambrian), and problematic conical fossils known as hyolithids (like the one pictured above, right). Many Early Cambrian invertebrates are known only from "small shelly fossils"  tiny plates, scales, spines, tubes, and so on. Many of these were probably pieces of the skeletons of larger animals. A few localities around the world that preserve soft-bodied fossils of the Cambrian show that the "Cambrian radiation" generated many unusual forms not easily comparable with anything today. The best-known of these sites is the legendary Burgess Shale (middle Cambrian) in the British Columbian Rocky Mountains. Sites in Utah , southern China, Siberia , and north Greenland are also noted for their unusually good preservation of non-mineralized fossils from the Cambrian.

One of these "weird wonders", first documented from the Burgess Shale, is Wiwaxia, depicted at lower left. Wiwaxia was an inch-long, creeping, scaly and spiny bottom dweller that may have been a relative of the molluscs , the annelids, or possibly an extinct animal group that combined features of both phyla. Stratigraphy A lot can happen in 40 million years, the approximate length of the Cambrian Period. Animals showed dramatic diversification during this period of Earth's history. This has been called the "Cambrian Explosion". When the fossil record is scrutinized closely, it turns out that the fastest growth in the number of major new animal groups took place during the as-yet-unnamed second and third stages (generally known as the Tommotian and Atdabanian stages) of the early Cambrian, a period of about 13 million years. In that time, the first undoubted fossil annelids, arthropods, brachiopods, echinoderms, molluscs, onychophorans, poriferans, and priapulids show up in rocks all over the world.

Stratigraphic boundaries are generally determined by the occurences of fossils. For instance, the trace fossil Treptichnus pedum marks the base of the Cambrian. This boundary is an unusual case, since stratigraphic boundaries are normally defined by the presence or absence of groups of fossils, called assemblages. In fact, much paleontological work is concerned with questions surrounding when and where stratigraphic boundaries should be defined. At first glance, this may not seem like important work, but consider this: if you wanted to know about the evolution of life on Earth, you would need a fairly accurate timeline. Questions such as: "how long did something stay the same?" or,"how fast did it change?" can only be assessed in the context of time. Tectonics and paleoclimate The Cambrian follows the Ediacaran Period, during which time the continents had been joined in a single supercontinent called Rodinia (from the Russian word for "homeland", rodina). As the Cambrian began, Rodinia began to fragment into smaller continents, which did not always correspond to the ones we see today.

The reconstruction below shows the rifting of Rodinia during the second stage (Tommotian) of the Cambrian . Green represents land above water at this time, red indicates mountains, light blue indicates shallow seas of the continental shelves, and dark blue denotes the deep ocean basins. (For clarity, the outlines of present-day continents have been superimposed on the map.) World climates were mild; there was no glaciation. Landmasses were scattered as a result of the fragmentation of the supercontinent Rodinia that had existed in the late Proterozoic. Most of North America lay in warm southern tropical and temperate latitudes, which supported the growth of extensive shallow-water archaeocyathid reefs all through the early Cambrian. Siberia, which also supported abundant reefs, was a separate continent due east of North America. Baltica  what is now Scandinavia, eastern Europe, and European Russia  lay to the south. Most of the rest of the continents were joined together in the supercontinent Gondwana, depicted on the right side of the map; South America, Africa, Antarctica, India, and Australia are all visible.

What is now China and east Asia was fragmented at the time, with the fragments visible north and west of Australia. Western Europe was also in pieces, with most of them lying northwest of what is now the north African coastline. The present-day southeastern United States are visible wedged between South America and Africa; they did not become part of North America for another 300 million years. Tectonism affected regions of Gondwana, primarily in what are now Australia, Antarctica, and Argentina. The continental plate movement and collisions during this period generated pressure and heat, resulting in the folding, faulting, and crumpling of rock and the formation of large mountain ranges. The Cambrian world was bracketed between two ice ages, one during the late Proterozoic and the other during the Ordovician . During these ice ages, the decrease in global temperature led to mass extinctions. Cooler conditions eliminated many warm water species, and glaciation lowered global sea level. However, during the Cambrian there was no significant ice formation. None of the continents were located at the poles so land temperatures remained mild. In fact, global climate was probably warmer and more uniform than it is today.

With the retreat of Proterozoic ice, the sea level rose significantly. Lowland areas such as Baltica were flooded and much of the world was covered by epeiric seas. This event opened up new habitats where marine invertebrates, such as trilobites, radiated and flourished. Plants had not yet evolved, and the terrestrial world was devoid of vegetation and inhospitable to life as we know it. Photosynthesis and primary production were the monopoly of bacteria and algal protists that populated the world's shallow seas. Also during the Cambrian, the oceans became oxygenated. Although there was plentiful atmospheric oxygen by the beginning of the period, it wasn't until the Cambrian that there was a sufficient reduction in the number of oxygen-depleting bacteria to permit higher oxygen levels in the waters. This dissolved oxygen may have triggered the "Cambrian Explosion"  when most of the major groups of animals, especially those with hard shells, first appeared in the fossil record. Localities Aldan River, Siberia, : This early Cambrian fauna tells us about the early evolution of animals with skeletons. Burgess Shale, British Columbia : Thousands of soft-bodied animal fossils paint us a picture of early marine life.

House Range, Utah : An array of Cambrian critters has been found in the Wheeler Shale and the Marjum Formation. Marble Mountains, California : Olenellid trilobites and more are found in this Mojave Desert locality. White-Inyo Mountains, California : Visit ancient Cambrian reefs in these mountains of eastern California. Resources * Dates from the International Commission on Stratigraphy's International Stratigraphic Chart, 2009. Page content written and completed by Ben M. Waggoner and Allen G. Collins, 11/22/1994; tectonics and paleoclimate material added by Karen Hsu, Myun Kang, Amy Lavarias, Kavitha Prabaker, and Cody Skaggs as part of a Biology 1B project for Section 112 under Brian R. Speer, 5/1/2000; Ben M.

Waggoner revised the Life content, 9/2001; Sarah Rieboldt updated the pages to reflect the Geological Society of America (GSA) 1999 Geologic Timescale, 11/2002; Dave Smith recombined the content into a single page, adapted it to the new site format and made some content updates, 7/6/2011; Acrothele and hyolith photos by Ben M. Waggoner; Olenellus photo by Dave Smith; source of Tommotian map unknown Paleozoic Era: Facts & Information Paleozoic Era: Facts & Information By Stephanie Pappas, Live Science Contributor | June 19, 2013 09:34pm ET MORE Credit: Alena Hovorkova The Paleozoic Era, which ran from about 542 million years ago to 251 million years ago, was a time of great change on Earth. The era began with the breakup of one supercontinent and the formation of another. Plants became widespread. And the first vertebrate animals colonized land.

Life in the Paleozoic The Paleozoic began with the Cambrian Period , 53 million years best known for ushering in an explosion of life on Earth. This "Cambrian explosion" included the evolution of arthropods (ancestors of today's insects and crustaceans) and chordates (animals with rudimentary spinal cords). In the Paleozoic Era, life flourished in the seas. After the Cambrian Period came the 45-million-year Ordovician Period, which is marked in the fossil record by an abundance of marine invertebrates. Perhaps the most famous of these invertebrates was the trilobite , an armored arthropod that scuttled around the seafloor for about 270 million years before going extinct. After the Ordovician Period came the Silurian Period (443 million years ago to 416 million years ago), which saw the spread of jawless fish throughout the seas. Mollusks and corals also thrived in the oceans, but the big news was what was happening on land: the first undisputed evidence of terrestrial life.

This was the time when plants evolved, though they most likely did not yet have leaves or the vascular tissue that allows modern plants to siphon up water and nutrients. Those developments would appear in the Devonian Period, the next geological period of the Paleozoic. Ferns appeared, as did the first trees. At the same time, the first vertebrates were colonizing the land. These vertebrates were called tetrapods , and they were widely diverse: Their appearance ranged from lizardlike to snakelike, and their size ranged from 4 inches (10 cm) long to 16 feet (5 meters) long, according to a study released in 2009 in the Journal of Anatomy. As the tetrapods took over, they had company: The Devonian Period saw the rise of the first land-living arthropods, including the earliest ancestors of spiders . The skeleton of Eryops, one of the earliest land-walking tetrapods. Credit: © Christine M. Janis Paleozoic evolution Life continued its march in the late Paleozoic.

The Carboniferous Period, which lasted from about 359 million years ago to 299 million years ago, answered the question, "Which came first — the chicken or the egg?" definitively. Long before birds evolved, tetrapods began laying eggs on land for the first time during this period, allowing them to break away from an amphibious lifestyle. Trilobites were fading as fish became more diverse. The ancestors of conifers appeared, and dragonflies ruled the skies. Tetrapods were becoming more specialized, and two new groups of animals evolved. The first were marine reptiles, including lizards and snakes. The second were the archosaurs, which would give rise to crocodiles, dinosaurs and birds. Most creepily, this era is sometimes referred to as the "Age of the Cockroaches," because roaches' ancient ancestor ( Archimylacris eggintoni ) was found all across the globe during the Carboniferous. The last period of the Paleozoic was the Permian Period, which began 299 million years ago and wrapped up 251 million years ago. This period would end with the largest mass extinction ever: the Permian extinction.

Before the Permian mass extinction, though, the warm seas teemed with life. Coral reefs flourished, providing shelter for fish and shelled creatures, such as nautiloids and ammonoids. Modern conifers and ginkgo trees evolved on land. Terrestrial vertebrates evolved to become herbivores, taking advantage of the new plant life that had colonized the land. Paleozoic geology and climate All this evolution took place against the backdrop of shifting continents and a changing climate. During the Cambrian Period of the Paleozoic, the continents underwent a change. They had been joined as one supercontinent, Rodinia, but during the Cambrian Period, Rodinia fragmented into Gondwana (consisting of what would eventually become the modern continents of the Southern Hemisphere) and smaller continents made up of bits and pieces of the land that would eventually make up today's northern continents. The Cambrian was warm worldwide, but would be followed by an ice age in the Ordovician, which caused glaciers to form, sending sea levels downward. Gondwana moved further south during the Ordovician, while the smaller continents started to move closer together.

In the Silurian Period, the land masses that would become North America, central and northern Europe, and western Europe moved even closer together. Sea levels rose again, creating shallow inland seas. In the Devonian, the northern land masses continued merging, and they finally joined together into the supercontinent Euramerica. Gondwana still existed, but the rest of the planet was ocean. By the last period of the Paleozoic, the Permian, Euramerica and Gondwana became one, forming perhaps the most famous supercontinent of them all: Pangaea . The giant ocean surrounding Pangaea was called Panthalassa. Pangaea's interior was likely very dry, because its massive size prevented water-bearing rain clouds from penetrating far beyond the coasts. Author Bio Stephanie Pappas, Live Science Contributor Stephanie Pappas is a contributing writer for Live Science. She covers the world of human and animal behavior, as well as paleontology and other science topics. Stephanie has a Bachelor of Arts in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz. She has ducked under a glacier in Switzerland and poked hot lava with a stick in Hawaii.

Stephanie hails from East Tennessee, the global center for salamander diversity. Follow Stephanie on Google+ . Stephanie Pappas, Live Science Contributor on Latest on Paleozoic Era: Facts & Information Cambrian Period & Cambrian Explosion: Facts & Information Credit: Bill Frische | Shutterstock The Cambrian Period is the first geological time period of the Paleozoic Era (the “time of ancient life”). This period lasted about 53 million years and marked a dramatic burst of evolutionary changes in life on Earth, known as the "Cambrian Explosion." Among the animals that evolved during this period were the chordates — animals with a dorsal nerve cord; hard-bodied brachiopods, which resembled clams; and arthropods — ancestors of spiders, insects and crustaceans. Though there is some scientific debate about what fossil strata should mark the beginning of the period, the International Geological Congress places the lower boundary of the period at 543 million years ago with the first appearance in the fossil record of worms that made horizontal burrows. The end of the Cambrian Period is marked by evidence in the fossil record of a mass extinction event about 490 million years ago.

The Cambrian Period was followed by the Ordovician Period. The period gets its name from Cambria, the Roman name for Wales, where Adam Sedgwick, one of the pioneers of geology, studied rock strata. Charles Darwin was one of his students. (Sedgwick, however, never accepted Darwin's theory of evolution and natural selection.) Climate of the Cambrian Period In the early Cambrian, Earth was generally cold but was gradually warming as the glaciers of the late Proterozoic Eon receded. Tectonic evidence suggests that the single supercontinent Rodinia broke apart and by the early to mid-Cambrian there were two continents. Gondwana, near the South Pole, was a supercontinent that later formed much of the land area of modern Africa, Australia, South America, Antarctica and parts of Asia. Laurentia, nearer the equator, was composed of landmasses that currently make up much of North America and part of Europe. Increased coastal area and flooding due to glacial retreat created more shallow sea environments. A fossilized Spartobranchus tenuis from the Burgess shale in Canada. The animal contains features of modern acorn worms and modern tube worms called pterobranches.

Credit: JB Caron At this point, no life yet existed on land; all life was aquatic. Very early in the Cambrian the sea floor was covered by a “mat” of microbial life above a thick layer of oxygen-free mud. The first multicellular life forms had evolved in the late Proterozoic to “graze” on the microbes. These multicellular organisms were the first to show evidence of a bilateral body plan. These near-microscopic “worms” began to burrow, mixing and oxygenating the mud of the ocean floor. During this time, dissolved oxygen was increasing in the water because of the presence of cyanobacteria. The first animals to develop calcium carbonate exoskeletons built coral reefs. [ Image Gallery: Cambrian Creatures: Primitive Sea Life ] The middle of the Cambrian Period began with an extinction event. Many of the reef-building organisms died out, as well as the most primitive trilobites. One hypothesis suggests that this was due to a temporary depletion of oxygen caused by an upwelling of cooler water from deep ocean areas. This upwelling eventually resulted in a variety of marine environments ranging from the deep ocean to the shallow coastal zones.

Scientists hypothesize that this increase in available ecological niches set the stage for the abrupt radiation in life forms commonly called the “ Cambrian Explosion .” Fossils of the Cambrian Period Scientists find some of the best specimens for the “evolutionary experiments” of the Cambrian Period in the fossil beds of the Sirius Passet formation in Greenland; Chenjiang, China; and the Burgess Shale of British Columbia. These formations are remarkable because the conditions of fossilization led to impressions of both hard and soft body parts and the most complete records of the varieties of organisms alive in the Cambrian Period. The Sirius Passet formation has fossils estimated to be from the early Cambrian Period. Arthropods are the most abundant, although the groups are not as diverse as those found in the later Burgess Shale formation. The Sirius Passet has the first fossil indications of complex predator/prey relationships. For example, Halkieria were slug-shaped animals with shell caps at either end. The rest of the body was covered in smaller armor plates over a soft snail-like “foot.” It is unclear whether they are more closely related to the annelids, such as modern-day earthworms and leeches, or are a primitive mollusk.

Some specimens have been found in curled up defensive postures like modern pill bugs. Predator/prey relationships provide intensive selection pressures that lead to rapid speciation and evolutionary change. The fearsome meter-long super-predator Anomalocaris. Credit: Katrina Kenny & University of Adelaide Burgess Shale fossils are from the late Cambrian. Diversity had increased dramatically. There are at least 12 species of trilobite in the Burgess Shale; whereas in the Sirius Passet, there are only two. It is clear that representatives of every animal phylum, excepting only the Bryozoa, existed by this time. The largest predator was Anomalocaris , a free-swimming animal that undulated through the water by flexing its lobed body. It had true compound eyes and two claw-tipped appendages in front of its mouth. It was the largest most fearsome predator of the Cambrian Period, but did not survive into the Ordovician. The earliest known chordate animal, the Pikaia, was about 1.5 inches (4 centimeters) long. Pikaia had a nerve cord that was visible as a ridge starting behind its head and extending almost to the tip of the body.

The fine detail preserved in the Burgess Shale clearly shows that Pikaia had the segmented muscle structure of later chordates and vertebrates. Haikouichythes, thought by some to be the earliest jawless fish, were also found in the Burgess Shale. A mass extinction event closed the Cambrian Period. Early Ordovician sediments found in South America are of glacial origin. James F. Miller of Southwest Missouri State University suggests that glaciers and a colder climate may have been the cause of the mass extinction of the fauna that evolved in the warm Cambrian oceans. Glacial ice would have also locked up much of the free ocean water, reducing both the oxygen in the water and the area available for shallow water species. Related pages GEOLOGIC HISTORY GEOLOGIC HISTORY Geologic Time When viewing this site and reading through the geologic history, it is important to remember that the Earth's geologic history covers a time span of about 4.6 billion years! The oldest rocks presently exposed in Valley Forge National Park are approximately 525 million years old, which means that only a small portion of the Earth's entire history is recorded within the park.

However, through techniques of geologic interpretation, scientists have constructed a timeline of geologic events that affected the Valley Forge area during the Paleozoic, Mesozoic, and Cenozoic eras. Figure borrowed from The geologic time scale above separates the geologic history of the Earth into major Eras and Periods. The ages of the major divisions are shown in millions of years before the present. Where does the geologic history of Valley Forge National Park fall within the bigger picture? Major events in the park's geologic history took place during the Paleozoic, Mesozoic and Cenozoic Eras. Read below to discover the specifics of these event. The oldest geologic events are discussed at the top of the page and more recent history is discussed at the bottom. Paleozoic Era About 525 million years ago during the Cambrian period, the coastline of the ancient North American continent was flooded by rising seas. At this time, sand accumulated along beaches, while muds and limy sediments were deposited offshore. Over time, the continued rise in sea level produced a layered stack of sedimentary rocks having sandstone at the base and carbonate rocks at the top.

In Valley Forge, the sediments deposited during this time were primarily sandstones, limestones, and dolostones. Marine life included trilobites, brachiopods, bryozoans, snails, clams, and sponges. The Cambrian Period marks the first time that multicellular organisms are known to have existed, but none of these organisms are noted in the rocks presently exposed at the surface within Valley Forge. Cambrian Chickies Quartzite. The Chickies formation underlies Mount Misery and Mount Joy, two topographic high points within the park. The unit consists largely of sand-sized quartz grains which probably were deposited in a beach environment. The original sandstone has been metamorphosed to quartzite under the influence of heat and pressure. Cambrian Ledger Dolostone. The Ledger dolostone underlies the area east and south of Mount Joy. Dolostone consists predominantly of the mineral dolomite (calcium and magnesium carbonate). Some carbonates form as chemical precipitates directly from sea water. Others are formed by marine organisms, such as coral, which extract calcium and carbonate from seawater to construct their shells.

The geologic setting began to change about 480 million years ago during the Ordovician period from a period of sediment accumulation to one of sediment erosion and rock deformation. For the next 200 million years, the Valley Forge area experienced intervals of mountain building activitiy that subjected rocks to deforming forces accompanied by increases in temperature and pressure. The most intense event to affect the region occurred near the beginning of this period when a volcanic island chain, much like the Japanese archipelago, collided with the North American continent. The collision caused originally horizontal layers of sedimentary rocks to be compressed into folds and to be thrust inland along large faults. Figure borrowed from At the end of the Paleozoic Era, all of the earths continents were assembled into a single landmass called Pangaea. Africa had collided with North America, producing the Appalachian Mountains in central Pennsylvania. Once the mountain-building activity ceased, natural weathering processes began wearing down the mountains. The Paleozoic Era Geologic Time | Paleozoic Era | Mesozoic Era | Cenozoic Era | The Paleozoic Era Global paleogeographic reconstruction of the Earth in the Early Cambrian period 540 million years ago. ( Courtesy Dr.

Ron Blakey ) Global paleogeographic reconstruction of the Earth in the Late Ordovician period 450 million years ago. ( Courtesy Dr. Ron Blakey ) Global paleogeographic reconstruction of the Earth in the Early Devonian period 400 million years ago. ( Courtesy Dr. Ron Blakey ) Global paleogeographic reconstruction of the Earth in the Pennsylvanian period 300 million years ago. ( Courtesy Dr. Ron Blakey ) The Paleozoic Era, meaning "ancient life" is the first of three eras that form a part of the Phanerozoic Eon, the other two periods being the Mesozoic and the Cenozoic . The Mesozoic is the age of the Dinosaurs and the Cenozoic is the era in which we now live. The Paleozoic Era spanned a longer period of time, from approximately 542 Ma to 251 Ma. Just as the Mesozoic is divided into periods ( Triassic , Jurassic , and Cretaceous ), the Paleozoic Era is also divided.

It contains six different periods which are: Cambrian (542-488 Ma) Carboniferous (359-299 Ma) Permian (299-251 Ma) The Paleozoic Era is bracketed by two major events in earth's history. It began with an unexplained explosion in animal life and ended with the world's largest mass-extinction known to man. The causes of these great events are currently unknown and under debate. Tectonics The tectonic activity during the Paleozoic era is similar to the way it has always behaved but were we to see what the earth looked like at the time, the continents would look almost completely alien to the way they are now. Contrary to popular belief, the continents on earth did not begin as the supercontinent Pangaea . Before Pangaea there were older continents. At the beginning of the Paleozoic the continents were massed in another supercontinent called Pannotia. This was at the end of a global ice age. As the era progressed the supercontinent split into several smaller continents, still unrecognizable from the continents we know today.

Near the end of the Paleozoic era the continents began to regroup as the supercontinent Pangaea. The collisions as the supercontinent was formed were strong enough to form mountain chains higher than the Himalayas. Among these mountain chains were the Appalachian mountains located on the east coast of North America, formed from a collision with what would become Africa. Environment Plant life took a little while to take off, but in the Carboniferous period the foliage thrived. The remains of the Carboniferous plant life are what form most of today's modern coal. However, this abundance in foliage declined by the Permian period and continued past the Paleozoic era into the Triassic period. At the start of the Paleozoic era the climate was moderate and shifting between stable and unstable. However, near the mid Paleozoic the climate stabilized to support all manner of land-roaming life. Near the end of the Paleozoic era the oxygen increased and carbon dioxide levels reached an all-time low causing severe ice ages in the Carboniferous period. Later, the continent Pangaea formed, creating a large surface area which caused extreme temperatures.

This climate deterioration near the end of the Paleozoic may have been the cause of the mass-extinction event that marked the end of the Paleozoic era. Animal Life The beginning of the Paleozoic era is marked by a sudden explosion of invertebrate animals, over 900 recorded species in the Cambrian period. It was only a few million years later that vertebrates appeared during the Ordovician period. The Devonian period showed an uprising in fish and other marine life. By the end of the Paleozoic era evolution had caused complex land and marine animals to exist. Much of the land was dominated by large reptiles, the early ancestors of the dinosaurs. However, the event that marked the end of the Paleozoic period was the massive extinction that wiped out nearly 96% of all marine life and 70% of land animals. Only a few species survived including some reptiles. Moving into the Mesozoic era and with the competition nearly eliminated those reptiles would eventually evolve to become the lords of the earth, also known as the Dinosaurs. Proterozoic Trilobite Geological Time Scale last revised 12 OCT 2014 by S. M.

Gon III The chart below depicts the geological periods during which trilobites existed. The presence of trilobites is one of the diagnostic features of the Paleozoic Era, the earliest era of the Phanerozoic Eon. The Paleozoic portion of the geological scale of eras at the left is expanded on the right as geological periods, and the time scale indicates how many millions of years ago (mya) each period persisted. The first appearance of trilobites defines the start of Series 2 of the Cambrian (521 mya), and they can be found in strata up to the upper Permian (252* mya), after which trilobites (among a large number of marine organisms) went extinct in the great catastrophe that removed over 90% of all species on earth. The Great Permian Extinction marks the end of the Paleozoic and the start of the Mesozoic. Trilobites are one of the few major groups of organisms that span the majority of the Paleozoic Era. The greatest numbers of trilobite species occurred during the Cambrian and Ordovician periods, after which trilobite extinction trends exceeded radiation events.

Toward the end of the Devonian most of the families and orders of trilobites were gone. There were much fewer species in the lone surviving order Proetida in the Carboniferous and Permian periods. Nevertheless, to have persisted for nearly 300 million years is a testimony to the successful design and adaptability of trilobites. Some scientists even hold out the faint hope that in poorly explored deep sea environments, trilobites may still exist, a holdover from truly ancient times. *The chart above (and below) are based on the International Commission of Stratigraphy 2008 revision of the Geological Time Scale. See for the full set of current charts in UNESCO and US standard colors.

The 2014 iteration makes some adjustments to the Era boundary dates: 541.0 for Precambrian-Cambrian, 485.4 for Cambrian-Ordovician, 443.4 for Ordovician-Silurian, 419.2 for Silurian- Devonian, 358.9 for Devonian-Carboniferous, 298.9 for Carboniferous-Permian, and 252.17 for End-Permian. First trilobites remain at 521. Trilobite Family Diversity over the Paleozoic Era Although trilobites are the signature organism of the Paleozoic, first appearing in the Early Cambrian , their peak diversity was in the early Paleozoic, and they began a general decline in the upper Paleozoic (despite bursts of adaptive radiations in the Ordovician, Silurian, and Devonian periods), and that ended with their extinction in the Late Permian .

By that time, they had dwindled to two families (Proetidae and Brachymetopidae, both in the order Proetida) and had long ceased to be a prominent feature of the marine biota. The chart below indicates changes in the diversity of the Trilobita over the periods of the Paleozoic Era, based on a figure (p 269) in the Treatise of Invertebrate Paleontology (1997) modified, especially in the Cambrian portion, via recent publications on biostratigraphy and trilobite persistence. * Cambrian ages and stage names in international standards have not yet all been established. All figures this page ï¿½2009 by S. M. Gon III created using Macromedia Freehand Extent of the Trilobite Orders over Geological Time Table of Geological Periods Health and Science > Science and Inventions > Physical Science Table of Geological Periods It is generally assumed that planets are formed by the accretion of gas and dust in a cosmic cloud, but there is no way of estimating the length of this process.

Our Earth acquired its present size, more or less, between 4 billion and 5 billion years ago. Life on Earth originated about 2 billion years ago, but there are no good fossil remains from periods earlier than the Cambrian, which began about 490 million years ago. The known geological history of Earth since the Precambrian Time is subdivided into three eras, each of which includes a number of periods. They, in turn, are subdivided into epochs and stage ages. In an epoch, a certain section may be especially well known because of rich fossil finds. New Geological Period In March 2004, geologists added a new time period to Earth's chronology—the Ediacaran Period. The Ediacaran Period lasted about 50 million years, from 600 million years ago to about 542 million years ago. It was the last period of the Precambrian's Neoproterozoic Era. Multicelled organisms first appeared during this time. This period is the first new one added in 120 years. Precambrian Time The Precambrian's lower limit is not defined, but ended about 542 million years ago.

The Precambrian encompasses about 90% of Earth's history. Eonothem eon

Question: What is the first geological period of the Paleozoic era?
Answer: Cambrian