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L_0002_T_0016 | Geology is the study of the solid Earth. Geologists study how rocks and minerals form. The way mountains rise up is part of geology. The way mountains erode away is another part. Geologists also study fossils and Earths history. There are many other branches of geology. There is so much to know about our home planet th... | {
"lesson_id": "L_0002",
"lesson_name": "earth science and its branches",
"source_split": "train",
"topic_name": "Geology"
} |
L_0002_T_0017 | Oceanography is the study of the oceans. The word oceanology might be more accurate, since ology is the study of. Graph is to write and refers to map making. But mapping the oceans is how oceanography started. More than 70% of Earths surface is covered with water. Almost all of that water is in the oceans. Scientists h... | {
"lesson_id": "L_0002",
"lesson_name": "earth science and its branches",
"source_split": "train",
"topic_name": "Oceanography"
} |
L_0002_T_0018 | Meteorologists dont study meteors they study the atmosphere! The word meteor refers to things in the air. Meteorology includes the study of weather patterns, clouds, hurricanes, and tornadoes. Meteorology is very important. Using radars and satellites, meteorologists work to predict, or forecast, the weather (Figure 1.... | {
"lesson_id": "L_0002",
"lesson_name": "earth science and its branches",
"source_split": "train",
"topic_name": "Climatology and Meteorology"
} |
L_0002_T_0019 | Environmental scientists study the ways that humans affect the planet we live on. We hope to find better ways of living that can also help the environment. Ecologists study lifeforms and the environments they live in (Figure 1.16). They try to predict the chain reactions that could occur when one part of the ecosystem ... | {
"lesson_id": "L_0002",
"lesson_name": "earth science and its branches",
"source_split": "train",
"topic_name": "Environmental Science"
} |
L_0002_T_0020 | Astronomy and astronomers have shown that the planets in our solar system are not the only planets in the universe. Over 530 planets were known outside our solar system in 2011. And there are billions of other planets! The universe also contains black holes, other galaxies, asteroids, comets, and nebula. As big as Eart... | {
"lesson_id": "L_0002",
"lesson_name": "earth science and its branches",
"source_split": "train",
"topic_name": "Astronomy"
} |
L_0003_T_0021 | Flowing water is a very important agent of erosion. Flowing water can erode rocks and soil. Water dissolves minerals from rocks and carries the ions. This process happens really slowly. But over millions of years, flowing water dissolves massive amounts of rock. Moving water also picks up and carries particles of soil ... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "How Flowing Water Causes Erosion and Deposition"
} |
L_0003_T_0022 | Faster-moving water has more energy. Therefore, it can carry larger particles. It can carry more particles. What causes water to move faster? The slope of the land over which the water flows is one factor. The steeper the slope, the faster the water flows. Another factor is the amount of water thats in the stream. Stre... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Water Speed and Erosion"
} |
L_0003_T_0023 | The size of particles determines how they are carried by flowing water. This is illustrated in Figure 10.2. Minerals that dissolve in water form salts. The salts are carried in solution. They are mixed thoroughly with the water. Small particles, such as clay and silt, are carried in suspension. They are mixed throughou... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Particle Size and Erosion"
} |
L_0003_T_0024 | Flowing water slows down when it reaches flatter land or flows into a body of still water. What do you think happens then? The water starts dropping the particles it was carrying. As the water slows, it drops the largest particles first. The smallest particles settle out last. | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Deposition by Water"
} |
L_0003_T_0025 | Water that flows over Earths surface includes runoff, streams, and rivers. All these types of flowing water can cause erosion and deposition. | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Erosion and Deposition by Surface Water"
} |
L_0003_T_0026 | When a lot of rain falls in a short period of time, much of the water is unable to soak into the ground. Instead, it runs over the land. Gravity causes the water to flow from higher to lower ground. As the runoff flows, it may pick up loose material on the surface, such as bits of soil and sand. Runoff is likely to cau... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Erosion by Runoff"
} |
L_0003_T_0027 | Streams often start in mountains, where the land is very steep. You can see an example in Figure 10.4. A mountain stream flows very quickly because of the steep slope. This causes a lot of erosion and very little deposition. The rapidly falling water digs down into the stream bed and makes it deeper. It carves a narrow... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Erosion by Mountain Streams"
} |
L_0003_T_0028 | Mountain streams may erode waterfalls. As shown in Figure 10.5, a waterfall forms where a stream flows from an area of harder to softer rock. The water erodes the softer rock faster than the harder rock. This causes the stream bed to drop down, like a step, creating a waterfall. As erosion continues, the waterfall grad... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "How a Waterfall Forms"
} |
L_0003_T_0029 | Rivers flowing over gentle slopes erode the sides of their channels more than the bottom. Large curves, called meanders, form because of erosion and deposition by the moving water. The curves are called meanders because they slowly wander over the land. You can see how this happens in Figure 10.6. As meanders erode fro... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Erosion by SlowFlowing Rivers"
} |
L_0003_T_0030 | When a stream or river slows down, it starts dropping its sediments. Larger sediments are dropped in steep areas, but smaller sediments can still be carried. Smaller sediments are dropped as the slope becomes less steep. Alluvial Fans In arid regions, a mountain stream may flow onto flatter land. The stream comes to a ... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Deposition by Streams and Rivers"
} |
L_0003_T_0031 | A flood occurs when a river overflows it banks. This might happen because of heavy rains. Floodplains As the water spreads out over the land, it slows down and drops its sediment. If a river floods often, the floodplain develops a thick layer of rich soil because of all the deposits. Thats why floodplains are usually g... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Deposition by Flood Waters"
} |
L_0003_T_0032 | Some water soaks into the ground. It travels down through tiny holes in soil. It seeps through cracks in rock. The water moves slowly, pulled deeper and deeper by gravity. Underground water can also erode and deposit material. | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Erosion and Deposition by Groundwater"
} |
L_0003_T_0033 | As groundwater moves through rock, it dissolves minerals. Some rocks dissolve more easily than others. Over time, the water may dissolve large underground holes, or caves. Groundwater drips from the ceiling to the floor of a cave. This water is rich in dissolved minerals. When the minerals come out of solution, they ar... | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Caves"
} |
L_0003_T_0034 | As erosion by groundwater continues, the ceiling of a cave may collapse. The rock and soil above it sink into the ground. This forms a sinkhole on the surface. You can see an example of a sinkhole in Figure 10.10. Some sinkholes are big enough to swallow vehicles and buildings. | {
"lesson_id": "L_0003",
"lesson_name": "erosion and deposition by flowing water",
"source_split": "train",
"topic_name": "Sinkholes"
} |
L_0004_T_0035 | All waves are the way energy travels through matter. Ocean waves are energy traveling through water. They form when wind blows over the surface of the ocean. Wind energy is transferred to the sea surface. Then, the energy is carried through the water by the waves. Figure 10.11 shows ocean waves crashing against rocks o... | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "What Are Waves"
} |
L_0004_T_0036 | Runoff, streams, and rivers carry sediment to the oceans. The sediment in ocean water acts like sandpaper. Over time, they erode the shore. The bigger the waves are and the more sediment they carry, the more erosion they cause. | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Wave Erosion"
} |
L_0004_T_0037 | Erosion by waves can create unique landforms (Figure 10.12). Wave-cut cliffs form when waves erode a rocky shoreline. They create a vertical wall of exposed rock layers. Sea arches form when waves erode both sides of a cliff. They create a hole in the cliff. Sea stacks form when waves erode the top of a sea arch. This ... | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Landforms From Wave Erosion"
} |
L_0004_T_0038 | Eventually, the sediment in ocean water is deposited. Deposition occurs where waves and other ocean motions slow. The smallest particles, such as silt and clay, are deposited away from shore. This is where water is calmer. Larger particles are deposited on the beach. This is where waves and other motions are strongest. | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Wave Deposition"
} |
L_0004_T_0039 | In relatively quiet areas along a shore, waves may deposit sand. Sand forms a beach, like the one in Figure 10.13. Many beaches include bits of rock and shell. You can see a close-up photo of beach deposits in Figure 10.14. | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Beaches"
} |
L_0004_T_0040 | Most waves strike the shore at an angle. This causes longshore drift. Longshore drift moves sediment along the shore. Sediment is moved up the beach by an incoming wave. The wave approaches at an angle to the shore. Water then moves straight offshore. The sediment moves straight down the beach with it. The sediment is ... | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Longshore Drift"
} |
L_0004_T_0041 | Deposits from longshore drift may form a spit. A spit is a ridge of sand that extends away from the shore. The end of the spit may hook around toward the quieter waters close to shore. You can see a spit in Figure 10.16. Waves may also deposit sediments to form sandbars and barrier islands. You can see examples of thes... | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Landforms Deposited by Waves"
} |
L_0004_T_0042 | Shores are attractive places to live and vacation. But development at the shore is at risk of damage from waves. Wave erosion threatens many homes and beaches on the ocean. This is especially true during storms, when waves may be much larger than normal. | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Protecting Shorelines"
} |
L_0004_T_0043 | Barrier islands provide natural protection to shorelines. Storm waves strike the barrier island before they reach the shore. People also build artificial barriers, called breakwaters. Breakwaters also protect the shoreline from incoming waves. You can see an example of a breakwater in Figure 10.18. It runs parallel to ... | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Breakwaters"
} |
L_0004_T_0044 | Longshore drift can erode the sediment from a beach. To keep this from happening, people may build a series of groins. A groin is wall of rocks or concrete that juts out into the ocean perpendicular to the shore. It stops waves from moving right along the beach. This stops the sand on the upcurrent side and reduces bea... | {
"lesson_id": "L_0004",
"lesson_name": "erosion and deposition by waves",
"source_split": "train",
"topic_name": "Groins"
} |
L_0006_T_0054 | Glaciers form when more snow falls than melts each year. Over many years, layer upon layer of snow compacts and turns to ice. There are two different types of glaciers: continental glaciers and valley glaciers. Each type forms some unique features through erosion and deposition. An example of each type is pictured in F... | {
"lesson_id": "L_0006",
"lesson_name": "erosion and deposition by glaciers",
"source_split": "train",
"topic_name": "How Glaciers Form"
} |
L_0006_T_0055 | Like flowing water, flowing ice erodes the land and deposits the material elsewhere. Glaciers cause erosion in two main ways: plucking and abrasion. Plucking is the process by which rocks and other sediments are picked up by a glacier. They freeze to the bottom of the glacier and are carried away by the flowing ice. Ab... | {
"lesson_id": "L_0006",
"lesson_name": "erosion and deposition by glaciers",
"source_split": "train",
"topic_name": "Erosion by Glaciers"
} |
L_0006_T_0056 | Valley glaciers form several unique features through erosion. You can see some of them in Figure 10.28. As a valley glacier flows through a V-shaped river valley, it scrapes away the sides of the valley. It carves a U-shaped valley with nearly vertical walls. A line called the trimline shows the highest level the glaci... | {
"lesson_id": "L_0006",
"lesson_name": "erosion and deposition by glaciers",
"source_split": "train",
"topic_name": "Erosion by Valley Glaciers"
} |
L_0006_T_0057 | Glaciers deposit their sediment when they melt. They drop and leave behind whatever was once frozen in their ice. Its usually a mixture of particles and rocks of all sizes, called glacial till. Water from the melting ice may form lakes or other water features. Figure 10.29 shows some of the landforms glaciers deposit w... | {
"lesson_id": "L_0006",
"lesson_name": "erosion and deposition by glaciers",
"source_split": "train",
"topic_name": "Deposition by Glaciers"
} |
L_0008_T_0064 | Fossils are preserved remains or traces of organisms that lived in the past. Most preserved remains are hard parts, such as teeth, bones, or shells. Examples of these kinds of fossils are pictured in Figure 11.1. Preserved traces can include footprints, burrows, or even wastes. Examples of trace fossils are also shown ... | {
"lesson_id": "L_0008",
"lesson_name": "fossils",
"source_split": "train",
"topic_name": "What Are Fossils"
} |
L_0008_T_0065 | The process by which remains or traces of living things become fossils is called fossilization. Most fossils are preserved in sedimentary rocks. | {
"lesson_id": "L_0008",
"lesson_name": "fossils",
"source_split": "train",
"topic_name": "How Fossils Form"
} |
L_0008_T_0066 | Most fossils form when a dead organism is buried in sediment. Layers of sediment slowly build up. The sediment is buried and turns into sedimentary rock. The remains inside the rock also turn to rock. The remains are replaced by minerals. The remains literally turn to stone. Fossilization is illustrated in Figure 11.2. | {
"lesson_id": "L_0008",
"lesson_name": "fossils",
"source_split": "train",
"topic_name": "Fossils in Sedimentary Rock"
} |
L_0008_T_0067 | Fossils may form in other ways. With complete preservation, the organism doesnt change much. As seen below, tree sap may cover an organism and then turn into amber. The original organism is preserved so that scientists might be able to study its DNA. Organisms can also be completely preserved in tar or ice. Molds and c... | {
"lesson_id": "L_0008",
"lesson_name": "fossils",
"source_split": "train",
"topic_name": "Other Ways Fossils Form"
} |
L_0008_T_0068 | Its very unlikely that any given organism will become a fossil. The remains of many organisms are consumed. Remains also may be broken down by other living things or by the elements. Hard parts, such as bones, are much more likely to become fossils. But even they rarely last long enough to become fossils. Organisms wit... | {
"lesson_id": "L_0008",
"lesson_name": "fossils",
"source_split": "train",
"topic_name": "Why Fossilization is Rare"
} |
L_0008_T_0069 | Of all the organisms that ever lived, only a tiny number became fossils. Still, scientists learn a lot from fossils. Fossils are our best clues about the history of life on Earth. | {
"lesson_id": "L_0008",
"lesson_name": "fossils",
"source_split": "train",
"topic_name": "Learning from Fossils"
} |
L_0008_T_0070 | Fossils give clues about major geological events. Fossils can also give clues about past climates. Fossils of ocean animals are found at the top of Mt. Everest. Mt. Everest is the highest mountain on Earth. These fossils show that the area was once at the bottom of a sea. The seabed was later uplifted to form the Himal... | {
"lesson_id": "L_0008",
"lesson_name": "fossils",
"source_split": "train",
"topic_name": "Fossil Clues"
} |
L_0008_T_0071 | Fossils are used to determine the ages of rock layers. Index fossils are the most useful for this. Index fossils are of organisms that lived over a wide area. They lived for a fairly short period of time. An index fossil allows a scientist to determine the age of the rock it is in. Trilobite fossils, as shown in Figure... | {
"lesson_id": "L_0008",
"lesson_name": "fossils",
"source_split": "train",
"topic_name": "Index Fossils"
} |
L_0009_T_0072 | The study of rock strata is called stratigraphy. The laws of stratigraphy can help scientists understand Earths past. The laws of stratigraphy are usually credited to a geologist from Denmark named Nicolas Steno. He lived in the 1600s. The laws are illustrated in Figure 11.6. Refer to the figure as you read about the l... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Laws of Stratigraphy"
} |
L_0009_T_0073 | Superposition refers to the position of rock layers and their relative ages. Relative age means age in comparison with other rocks, either younger or older. The relative ages of rocks are important for understanding Earths history. New rock layers are always deposited on top of existing rock layers. Therefore, deeper l... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Law of Superposition"
} |
L_0009_T_0074 | Rock layers extend laterally, or out to the sides. They may cover very broad areas, especially if they formed at the bottom of ancient seas. Erosion may have worn away some of the rock, but layers on either side of eroded areas will still match up. Look at the Grand Canyon in Figure 11.8. Its a good example of lateral ... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Law of Lateral Continuity"
} |
L_0009_T_0075 | Sediments were deposited in ancient seas in horizontal, or flat, layers. If sedimentary rock layers are tilted, they must have moved after they were deposited. | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Law of Original Horizontality"
} |
L_0009_T_0076 | Rock layers may have another rock cutting across them, like the igneous rock in Figure 11.9. Which rock is older? To determine this, we use the law of cross-cutting relationships. The cut rock layers are older than the rock that cuts across them. | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Law of CrossCutting Relationships"
} |
L_0009_T_0077 | Geologists can learn a lot about Earths history by studying sedimentary rock layers. But in some places, theres a gap in time when no rock layers are present. A gap in the sequence of rock layers is called an unconformity. Look at the rock layers in Figure 11.10. They show a feature called Huttons unconformity. The unc... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Unconformities"
} |
L_0009_T_0078 | When rock layers are in the same place, its easy to give them relative ages. But what if rock layers are far apart? What if they are on different continents? What evidence is used to match rock layers in different places? | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Matching Rock Layers"
} |
L_0009_T_0079 | Some rock layers extend over a very wide area. They may be found on more than one continent or in more than one country. For example, the famous White Cliffs of Dover are on the coast of southeastern England. These distinctive rocks are matched by similar white cliffs in France, Belgium, Holland, Germany, and Denmark (... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Widespread Rock Layers"
} |
L_0009_T_0080 | Like index fossils, key beds are used to match rock layers. A key bed is a thin layer of rock. The rock must be unique and widespread. For example, a key bed from around the time that the dinosaurs went extinct is very important. A thin layer of clay was deposited over much of Earths surface. The clay has large amount ... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Key Beds"
} |
L_0009_T_0081 | Index fossils are commonly used to match rock layers in different places. You can see how this works in Figure | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Using Index Fossils"
} |
L_0009_T_0082 | Earth formed 4.5 billion years ago. Geologists divide this time span into smaller periods. Many of the divisions mark major events in life history. | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "The Geologic Time Scale"
} |
L_0009_T_0083 | Divisions in Earth history are recorded on the geologic time scale. For example, the Cretaceous ended when the dinosaurs went extinct. European geologists were the first to put together the geologic time scale. So, many of the names of the time periods are from places in Europe. The Jurassic Period is named for the Jur... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Dividing Geologic Time"
} |
L_0009_T_0084 | To create the geologic time scale, geologists correlated rock layers. Stenos laws were used to determine the relative ages of rocks. Older rocks are at the bottom and younger rocks are at the top. The early geologic time scale could only show the order of events. The discovery of radioactivity in the late 1800s changed... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Putting Events in Order"
} |
L_0009_T_0085 | The largest blocks of time on the geologic time scale are called eons. Eons are split into eras. Each era is divided into periods. Periods may be further divided into epochs. Geologists may just use early or late. An example is late Jurassic, or early Cretaceous. Figure 11.13 shows you what the geologic time scale look... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Divisions of the Geologic Time Scale"
} |
L_0009_T_0086 | The geologic time scale may include illustrations of how life on Earth has changed. Major events on Earth may also be shown. These include the formation of the major mountains or the extinction of the dinosaurs. Figure 11.14 is a different kind of the geologic time scale. It shows how Earths environment and life forms ... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Life and the Geologic Time Scale"
} |
L_0009_T_0087 | We now live in the Phanerozoic Eon, the Cenozoic Era, the Quaternary Period, and the Holocene Epoch. Phanero- zoic means visible life. During this eon, rocks contain visible fossils. Before the Phanerozoic, life was microscopic. The Cenozoic Era means new life. It encompasses the most recent forms of life on Earth. The... | {
"lesson_id": "L_0009",
"lesson_name": "relative ages of rocks",
"source_split": "train",
"topic_name": "Your Place in Geologic Time"
} |
L_0010_T_0088 | Radioactive decay is the breakdown of unstable elements into stable elements. To understand this process, recall that the atoms of all elements contain the particles protons, neutrons, and electrons. | {
"lesson_id": "L_0010",
"lesson_name": "absolute ages of rocks",
"source_split": "train",
"topic_name": "Radioactive Decay"
} |
L_0010_T_0089 | An element is defined by the number of protons it contains. All atoms of a given element contain the same number of protons. The number of neutrons in an element may vary. Atoms of an element with different numbers of neutrons are called isotopes. Consider carbon as an example. Two isotopes of carbon are shown in Figur... | {
"lesson_id": "L_0010",
"lesson_name": "absolute ages of rocks",
"source_split": "train",
"topic_name": "Isotopes"
} |
L_0010_T_0090 | Like other unstable isotopes, carbon-14 breaks down, or decays. For carbon-14 decay, each carbon-14 atom loses an alpha particle. It changes to a stable atom of nitrogen-14. This is illustrated in Figure 11.17. The decay of an unstable isotope to a stable element occurs at a constant rate. This rate is different for ea... | {
"lesson_id": "L_0010",
"lesson_name": "absolute ages of rocks",
"source_split": "train",
"topic_name": "Decay of Unstable Isotopes"
} |
L_0010_T_0091 | The rate of decay of unstable isotopes can be used to estimate the absolute ages of fossils and rocks. This type of dating is called radiometric dating. | {
"lesson_id": "L_0010",
"lesson_name": "absolute ages of rocks",
"source_split": "train",
"topic_name": "Radiometric Dating"
} |
L_0010_T_0092 | The best-known method of radiometric dating is carbon-14 dating. A living thing takes in carbon-14 (along with stable carbon-12). As the carbon-14 decays, it is replaced with more carbon-14. After the organism dies, it stops taking in carbon. That includes carbon-14. The carbon-14 that is in its body continues to decay... | {
"lesson_id": "L_0010",
"lesson_name": "absolute ages of rocks",
"source_split": "train",
"topic_name": "Carbon14 Dating"
} |
L_0010_T_0093 | The isotopes in Table 11.1 are used to date igneous rocks. These isotopes have much longer half-lives than carbon- 14. Because they decay more slowly, they can be used to date much older specimens. Which of these isotopes could be used to date a rock that formed half a million years ago? Unstable Isotope Decays to At a... | {
"lesson_id": "L_0010",
"lesson_name": "absolute ages of rocks",
"source_split": "train",
"topic_name": "Other Radioactive Isotopes"
} |
L_0011_T_0094 | Our solar system began about 5 billion years ago. The Sun, planets and other solar system objects all formed at about the same time. | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "Formation the Solar System"
} |
L_0011_T_0095 | The Sun and planets formed from a giant cloud of gas and dust. This was the solar nebula. The cloud contracted and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster, and formed into a disk. Scientists think the solar system at that time looked like these disk-shaped objects ... | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "The Solar Nebula"
} |
L_0011_T_0096 | Temperatures and pressures at the center of the cloud were extreme. It was so hot that nuclear fusion reactions began. In these reactions hydrogen fuses to make helium. Extreme amounts of energy are released. Our Sun became a star! Material in the disk surrounding the Sun collided. Small particles collided and became r... | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "Solar System Bodies Form"
} |
L_0011_T_0097 | Material at a similar distances from the Sun collided together to form each of the planets. Earth grew from material in its part of space. Moons origin was completely different from Earths. | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "Formation Earth and Moon"
} |
L_0011_T_0098 | Earth formed like the other planets. Different materials in its region of space collided. Eventually the material made a planet. All of the collisions caused Earth to heat up. Rock and metal melted. The molten material separated into layers. Gravity pulled the denser material into the center. The lighter elements rose ... | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "Earth Forms"
} |
L_0011_T_0099 | This model for how the Moon formed is the best fit of all of the data scientists have about the Moon. In the early solar system there was a lot of space debris. Asteroids flew around, sometimes striking the planets. An asteroid the size of Mars smashed into Earth. The huge amount of energy from the impact melted most o... | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "Moon Forms"
} |
L_0011_T_0100 | An atmosphere is the gases that surround a planet. The early Earth had no atmosphere. Conditions were so hot that gases were not stable. | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "Formation of the Atmosphere and Oceans"
} |
L_0011_T_0101 | Earths first atmosphere was different from the current one. The gases came from two sources. Volcanoes spewed gases into the air. Comets carried in ices from outer space. These ices warmed and became gases. Nitrogen, carbon dioxide, hydrogen, and water vapor, or water in gas form, were in the first atmosphere (Figure 1... | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "Earths First Atmosphere"
} |
L_0011_T_0102 | Earths atmosphere slowly cooled. Once it was cooler, water vapor could condense. It changed back to its liquid form. Liquid water could fall to Earths surface as rain. Over millions of years water collected to form the oceans. Water began to cycle on Earth as water evaporated from the oceans and returned again as rainf... | {
"lesson_id": "L_0011",
"lesson_name": "the origin of earth",
"source_split": "train",
"topic_name": "The Early Oceans"
} |
L_0012_T_0103 | The earliest crust was probably basalt. It may have resembled the current seafloor. This crust formed before there were any oceans. More than 4 billion years ago, continental crust appeared. The first continents were very small compared with those today. | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Early Continents"
} |
L_0012_T_0104 | Continents grow when microcontinents, or small continents, collide with each other or with a larger continent. Oceanic island arcs also collide with continents to make them grow. | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Continents Grow"
} |
L_0012_T_0105 | There are times in Earth history when all of the continents came together to form a supercontinent. Supercontinents come together and then break apart. Pangaea was the last supercontinent on Earth, but it was not the first. The supercontinent before Pangaea is called Rodinia. Rodinia contained about 75% of the continen... | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Supercontinents"
} |
L_0012_T_0106 | Since the early Earth was very hot, mantle convection was very rapid. Plate tectonics likely moved very quickly. The early Earth was a very active place with abundant volcanic eruptions and earthquakes. The remnants of these early rocks are now seen in the ancient cores of the continents. | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Early Plate Tectonics"
} |
L_0012_T_0107 | For the first 4 billion years of Earth history there is only a little evidence of life. Organisms were tiny and soft and did not fossilize well. But scientists use a variety of ways to figure out what this early life was like. | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Ancient Life"
} |
L_0012_T_0108 | Life probably began in the oceans. No one knows exactly how or when. Life may have originated more than once. If life began before the Moon formed, that impact would have wiped it out and it would have had to originate again. Eventually conditions on Earth became less violent. The planet could support life. The first o... | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Life Begins"
} |
L_0012_T_0109 | Early cells took nutrients from the water. Eventually the nutrients would have become less abundant. Around 3 billion years ago, photosynthesis began. Organisms could make their own food from sunlight and inorganic molecules. From these ingredients they made chemical energy that they used. Oxygen is a waste product of ... | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Oxygen Enters the Atmosphere"
} |
L_0012_T_0110 | The first organisms to photosynthesize were cyanobacteria. These organisms may have been around as far back as 3.5 billion years and are still alive today (Figure 12.7). Now they are called blue-green algae. They are common in lakes and seas and account for 20% to 30% of photosynthesis today. | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Early Organisms"
} |
L_0012_T_0111 | Eukaryotes evolved about 2 billion years ago. Unlike prokaryotes, eukaryotes have a cell nucleus. They have more structures and are better organized. Organelles within a eukaryote can perform certain functions. Some supply energy; some break down wastes. Eukaryotes were better able to live and so became the dominant li... | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "Life Gets More Complex"
} |
L_0012_T_0112 | For life to become even more complex, multicellular organisms needed to evolve. Prokaryotes and eukaryotes can be multicellular. Toward the end of the Precambrian, the Ediacara Fauna evolved (Figure 12.8). These are the fossils discovered by Walcott in the introduction to the next section. The Ediacara was extremely di... | {
"lesson_id": "L_0012",
"lesson_name": "early earth",
"source_split": "train",
"topic_name": "MultiCellular Life Originates"
} |
L_0014_T_0131 | Water is a simple chemical compound. Each molecule of water contains two hydrogen atoms (H2 ) and one oxygen atom (O). Thats why the chemical formula for water is H2 O. If water is so simple, why is it special? Water is one of the few substances that exists on Earth in all three states of matter. Water occurs as a gas,... | {
"lesson_id": "L_0014",
"lesson_name": "water on earth",
"source_split": "train",
"topic_name": "What Is Water"
} |
L_0014_T_0132 | Earth is often called the water planet. Figure 13.1 shows why. If astronauts see Earth from space, this is how it looks. Notice how blue the planet appears. Thats because oceans cover much of Earths surface. Water is also found in the clouds that rise above the planet. Most of Earths water is salt water in the oceans. ... | {
"lesson_id": "L_0014",
"lesson_name": "water on earth",
"source_split": "train",
"topic_name": "Where Is Earths Freshwater"
} |
L_0014_T_0133 | Did you ever wonder where the water in your glass came from or where its been? The next time you take a drink of water, think about this. Each water molecule has probably been around for billions of years. Thats because Earths water is constantly recycled. | {
"lesson_id": "L_0014",
"lesson_name": "water on earth",
"source_split": "train",
"topic_name": "The Water Cycle"
} |
L_0014_T_0134 | Water is recycled through the water cycle. The water cycle is the movement of water through the oceans, atmo- sphere, land, and living things. The water cycle is powered by energy from the Sun. Figure 13.3 diagrams the water cycle. | {
"lesson_id": "L_0014",
"lesson_name": "water on earth",
"source_split": "train",
"topic_name": "How Water Is Recycled"
} |
L_0014_T_0135 | Water keeps changing state as it goes through the water cycle. This means that it can be a solid, liquid, or gas. How does water change state? How does it keep moving through the cycle? As Figure 13.3 shows, several processes are involved. Evaporation changes liquid water to water vapor. Energy from the Sun causes wate... | {
"lesson_id": "L_0014",
"lesson_name": "water on earth",
"source_split": "train",
"topic_name": "Processes in the Water Cycle"
} |
L_0015_T_0136 | Look at the pictures of flowing water in Figure 13.4. A waterfall tumbles down a mountainside. A brook babbles through a forest. A river slowly meanders through a broad valley. What do all these forms of flowing water have in common? They are all streams. | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "Streams and Rivers"
} |
L_0015_T_0137 | A stream is a body of freshwater that flows downhill in a channel. The channel of a stream has a bottom, or bed, and sides called banks. Any size body of flowing water can be called a stream. Usually, though, a large stream is called a river. | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "What Are Streams and Rivers"
} |
L_0015_T_0138 | All streams and rivers have several features in common. These features are shown in (Figure 13.5). The place where a stream or river starts is its source. The source might be a spring, where water flows out of the ground. Or the source might be water from melting snow on a mountain top. A single stream may have multipl... | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "Features of Streams and Rivers"
} |
L_0015_T_0139 | All of the land drained by a river system is called its basin, or watershed. One river systems basin is separated from another river systems basin by a divide. The divide is created by the highest points between the two river basins. Precipitation that falls within a river basin always flows toward that river. Precipit... | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "River Basins and Divides"
} |
L_0015_T_0140 | After a heavy rain, you may find puddles of water standing in low spots. The same principle explains why water collects in ponds and lakes. Water travels downhill, so a depression in the ground fills with standing water. A pond is a small body of standing water. A lake is a large body of standing water. Most lakes have... | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "Ponds and Lakes"
} |
L_0015_T_0141 | Ponds and lakes may get their water from several sources. Some falls directly into them as precipitation. Some enters as runoff and some from streams and rivers. Water leaves ponds and lakes through evaporation and also as outflow. | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "Water in Ponds and Lakes"
} |
L_0015_T_0142 | The depression that allows water to collect to form a lake may come about in a variety of ways. The Great Lakes, for example, are glacial lakes. A glacial lake forms when a glacier scrapes a large hole in the ground. When the glacier melts, the water fills the hole and forms a lake. Over time, water enters the lake fro... | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "How Lakes Form"
} |
L_0015_T_0143 | Some of Earths freshwater is found in wetlands. A wetland is an area that is covered with water, or at least has very soggy soil, during all or part of the year. Certain species of plants thrive in wetlands, and they are rich ecosystems. Freshwater wetlands are usually found at the edges of steams, rivers, ponds, or la... | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "Wetlands"
} |
L_0015_T_0144 | Not all wetlands are alike, as you can see from Figure 13.9. Wetlands vary in how wet they are and how much of the year they are soaked. Wetlands also vary in the kinds of plants that live in them. This depends mostly on the climate where the wetland is found. Types of wetlands include marshes, swamps, and bogs. A mars... | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "Types of Freshwater Wetlands"
} |
L_0015_T_0145 | People used to think that wetlands were useless. Many wetlands were filled in with rocks and soil to create lands that were then developed with roads, golf courses, and buildings. Now we know that wetlands are very important. Laws have been passed to help protect them. Why are wetlands so important? Wetlands have great... | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "Importance of Wetlands"
} |
L_0015_T_0146 | A flood occurs when so much water enters a stream or river that it overflows its banks. Flood waters from a river are shown in Figure 13.10. Like this flood, many floods are caused by very heavy rains. Floods may also occur when deep snow melts quickly in the spring. Floods are a natural part of the water cycle, but th... | {
"lesson_id": "L_0015",
"lesson_name": "surface water",
"source_split": "train",
"topic_name": "Floods"
} |
L_0016_T_0147 | Freshwater below Earths surface is called groundwater. The water infiltrates, or seeps down into, the ground from the surface. How does this happen? And where does the water go? | {
"lesson_id": "L_0016",
"lesson_name": "groundwater",
"source_split": "train",
"topic_name": "Groundwater"
} |
L_0016_T_0148 | Water infiltrates the ground because soil and rock are porous. Between the grains are pores, or tiny holes. Since water can move through this rock it is permeable. Eventually, the water reaches a layer of rock that is not porous and so is impermeable. Water stops moving downward when it reaches this layer of rock. Look... | {
"lesson_id": "L_0016",
"lesson_name": "groundwater",
"source_split": "train",
"topic_name": "Porous and Impermeable Rock"
} |
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