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L_0764 | using electromagnetism | DQ_011459 | electromagnetism_9086.png | image | question_images/electromagnetism_9086.png |
L_0764 | using electromagnetism | DQ_011461 | electromagnetism_9088.png | image | question_images/electromagnetism_9088.png |
L_0764 | using electromagnetism | DQ_011463 | electromagnetism_9089.png | image | question_images/electromagnetism_9089.png |
L_0764 | using electromagnetism | DQ_011466 | electromagnetism_9091.png | image | question_images/electromagnetism_9091.png |
L_0764 | using electromagnetism | DQ_011472 | electromagnetism_9092.png | image | question_images/electromagnetism_9092.png |
L_0764 | using electromagnetism | DQ_011474 | electromagnetism_9093.png | image | question_images/electromagnetism_9093.png |
L_0769 | solids liquids gases and plasmas | DQ_011479 | states_of_matter_17613.png | image | abc_question_images/states_of_matter_17613.png |
L_0769 | solids liquids gases and plasmas | DQ_011483 | states_of_matter_17618.png | image | abc_question_images/states_of_matter_17618.png |
L_0769 | solids liquids gases and plasmas | DQ_011487 | states_of_matter_19251.png | image | abc_question_images/states_of_matter_19251.png |
L_0769 | solids liquids gases and plasmas | DQ_011488 | states_of_matter_19252.png | image | abc_question_images/states_of_matter_19252.png |
L_0769 | solids liquids gases and plasmas | DQ_011490 | states_of_matter_19255.png | image | abc_question_images/states_of_matter_19255.png |
L_0769 | solids liquids gases and plasmas | DQ_011492 | states_of_matter_19256.png | image | abc_question_images/states_of_matter_19256.png |
L_0769 | solids liquids gases and plasmas | DQ_011493 | states_of_matter_19258.png | image | abc_question_images/states_of_matter_19258.png |
L_0769 | solids liquids gases and plasmas | DQ_011497 | states_of_matter_7613.png | image | question_images/states_of_matter_7613.png |
L_0769 | solids liquids gases and plasmas | DQ_011501 | states_of_matter_7614.png | image | question_images/states_of_matter_7614.png |
L_0769 | solids liquids gases and plasmas | DQ_011504 | states_of_matter_7617.png | image | question_images/states_of_matter_7617.png |
L_0769 | solids liquids gases and plasmas | DQ_011512 | states_of_matter_7618.png | image | question_images/states_of_matter_7618.png |
L_0769 | solids liquids gases and plasmas | DQ_011516 | states_of_matter_9251.png | image | question_images/states_of_matter_9251.png |
L_0769 | solids liquids gases and plasmas | DQ_011523 | states_of_matter_9252.png | image | question_images/states_of_matter_9252.png |
L_0769 | solids liquids gases and plasmas | DQ_011527 | states_of_matter_9254.png | image | question_images/states_of_matter_9254.png |
L_0769 | solids liquids gases and plasmas | DQ_011534 | states_of_matter_9255.png | image | question_images/states_of_matter_9255.png |
L_0769 | solids liquids gases and plasmas | DQ_011540 | states_of_matter_9257.png | image | question_images/states_of_matter_9257.png |
L_0769 | solids liquids gases and plasmas | DQ_011545 | states_of_matter_9258.png | image | question_images/states_of_matter_9258.png |
L_0771 | changes of state | DQ_011553 | evaporation_and_sublimation_18077.png | image | abc_question_images/evaporation_and_sublimation_18077.png |
L_0771 | changes of state | DQ_011557 | evaporation_and_sublimation_18079.png | image | abc_question_images/evaporation_and_sublimation_18079.png |
L_0771 | changes of state | DQ_011559 | state_change_17600.png | image | abc_question_images/state_change_17600.png |
L_0771 | changes of state | DQ_011564 | state_change_17601.png | image | abc_question_images/state_change_17601.png |
L_0771 | changes of state | DQ_011567 | state_change_17602.png | image | abc_question_images/state_change_17602.png |
L_0771 | changes of state | DQ_011569 | state_change_17606.png | image | abc_question_images/state_change_17606.png |
L_0771 | changes of state | DQ_011570 | evaporation_and_sublimation_6876.png | image | question_images/evaporation_and_sublimation_6876.png |
L_0771 | changes of state | DQ_011577 | evaporation_and_sublimation_6877.png | image | question_images/evaporation_and_sublimation_6877.png |
L_0771 | changes of state | DQ_011581 | evaporation_and_sublimation_6880.png | image | question_images/evaporation_and_sublimation_6880.png |
L_0771 | changes of state | DQ_011588 | evaporation_and_sublimation_8075.png | image | question_images/evaporation_and_sublimation_8075.png |
L_0771 | changes of state | DQ_011595 | evaporation_and_sublimation_8076.png | image | question_images/evaporation_and_sublimation_8076.png |
L_0771 | changes of state | DQ_011602 | evaporation_and_sublimation_8077.png | image | question_images/evaporation_and_sublimation_8077.png |
L_0771 | changes of state | DQ_011608 | evaporation_and_sublimation_8078.png | image | question_images/evaporation_and_sublimation_8078.png |
L_0771 | changes of state | DQ_011613 | evaporation_and_sublimation_8080.png | image | question_images/evaporation_and_sublimation_8080.png |
L_0771 | changes of state | DQ_011620 | evaporation_and_sublimation_8081.png | image | question_images/evaporation_and_sublimation_8081.png |
L_0771 | changes of state | DQ_011626 | evaporation_and_sublimation_8082.png | image | question_images/evaporation_and_sublimation_8082.png |
L_0771 | changes of state | DQ_011633 | evaporation_and_sublimation_8083.png | image | question_images/evaporation_and_sublimation_8083.png |
L_0771 | changes of state | DQ_011639 | state_change_7600.png | image | question_images/state_change_7600.png |
L_0771 | changes of state | DQ_011645 | state_change_7601.png | image | question_images/state_change_7601.png |
L_0771 | changes of state | DQ_011650 | state_change_7602.png | image | question_images/state_change_7602.png |
L_0771 | changes of state | DQ_011657 | state_change_7603.png | image | question_images/state_change_7603.png |
L_0771 | changes of state | DQ_011664 | state_change_7604.png | image | question_images/state_change_7604.png |
L_0771 | changes of state | DQ_011671 | state_change_7608.png | image | question_images/state_change_7608.png |
L_0771 | changes of state | DQ_011677 | state_change_7609.png | image | question_images/state_change_7609.png |
L_0771 | changes of state | DQ_011684 | state_change_7610.png | image | question_images/state_change_7610.png |
L_0771 | changes of state | DQ_011690 | state_change_8165.png | image | question_images/state_change_8165.png |
L_0002 | earth science and its branches | 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 that most geologists become specialists in one area. For example, a mineralogist studies minerals, as seen in (Figure 1.11). Some volcanologists brave molten lava to study volcanoes. Seismologists monitor earthquakes worldwide to help protect people and property from harm (Figure 1.11). Paleontologists are interested in fossils and how ancient organisms lived. Scientists who compare the geology of other planets to Earth are planetary geologists. Some geologists study the Moon. Others look for petroleum. Still others specialize in studying soil. Some geologists can tell how old rocks are and determine how different rock layers formed. There is probably an expert in almost anything you can think of related to Earth! Geologists might study rivers and lakes, the underground water found between soil and rock particles, or even water that is frozen in glaciers. Earth scientists also need geographers who explore the features of Earths surface and work with cartographers, who make maps. Studying the layers of rock beneath the surface helps us to understand the history of planet Earth (Figure 1.12). | text | null |
L_0002 | earth science and its branches | 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 have visited the deepest parts of the ocean in submarines. Remote vehicles go where humans cant. Yet much of the ocean remains unexplored. Some people call the ocean the last frontier. Humans have had a big impact on the oceans. Populations of fish and other marine species have been overfished. Contaminants are polluting the waters. Global warming is melting the thick ice caps and warming the water. Warmer water expands and, along with water from the melting ice caps, causes sea levels to rise. There are many branches of oceanography. Physical oceanography is the study of water movement, like waves and ocean currents (Figure 1.13). Marine geology looks at rocks and structures in the ocean basins. Chemical oceanography studies the natural elements in ocean water. Marine biology looks at marine life. | text | null |
L_0002 | earth science and its branches | 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 have visited the deepest parts of the ocean in submarines. Remote vehicles go where humans cant. Yet much of the ocean remains unexplored. Some people call the ocean the last frontier. Humans have had a big impact on the oceans. Populations of fish and other marine species have been overfished. Contaminants are polluting the waters. Global warming is melting the thick ice caps and warming the water. Warmer water expands and, along with water from the melting ice caps, causes sea levels to rise. There are many branches of oceanography. Physical oceanography is the study of water movement, like waves and ocean currents (Figure 1.13). Marine geology looks at rocks and structures in the ocean basins. Chemical oceanography studies the natural elements in ocean water. Marine biology looks at marine life. | text | null |
L_0002 | earth science and its branches | 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 1.14). The atmosphere is a thin layer of gas that surrounds Earth. Climatologists study the atmosphere. These scientists work to understand the climate as it is now. They also study how climate will change in response to global warming. The atmosphere contains small amounts of carbon dioxide. Climatologists have found that humans are putting a lot of extra carbon dioxide into the atmosphere. This is mostly from burning fossil fuels. The extra carbon dioxide traps heat from the Sun. Trapped heat causes the atmosphere to heat up. We call this global warming (Figure 1.15). | text | null |
L_0002 | earth science and its branches | 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 1.14). The atmosphere is a thin layer of gas that surrounds Earth. Climatologists study the atmosphere. These scientists work to understand the climate as it is now. They also study how climate will change in response to global warming. The atmosphere contains small amounts of carbon dioxide. Climatologists have found that humans are putting a lot of extra carbon dioxide into the atmosphere. This is mostly from burning fossil fuels. The extra carbon dioxide traps heat from the Sun. Trapped heat causes the atmosphere to heat up. We call this global warming (Figure 1.15). | text | null |
L_0002 | earth science and its branches | 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 is disrupted. | text | null |
L_0002 | earth science and its branches | 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 Earth seems, the entire universe is vastly more enormous. Earth is just a tiny part of our universe. Astronomers use many tools to study things in space. Earth-orbiting telescopes view stars and galaxies from the darkness of space (Figure 1.17). They may have optical and radio telescopes to see things that the human eye cant see. Spacecraft travel great distances to send back information on faraway places. Astronomers ask a wide variety of questions. How do strong bursts of energy from the Sun, called solar flares, affect communications? How might an impact from an asteroid affect life on Earth? What are the properties of black holes? Astronomers ask bigger questions too. How was the universe created? Is there life on other planets? Are there resources on other planets that people could use? Astronomers use what Earth scientists know to make comparisons with other planets. | text | null |
L_0003 | erosion and deposition by flowing water | 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 and rock. The ability to erode is affected by the velocity, or speed, of the water. The size of the eroded particles depends on the velocity of the water. Eventually, the water deposits the materials. As water slows, larger particles are deposited. As the water slows even more, smaller particles are deposited. The graph in Figure 10.1 shows how water velocity and particle size influence erosion and deposition. | text | null |
L_0003 | erosion and deposition by flowing water | 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. Streams with a lot of water flow faster than streams that are nearly dry. | text | null |
L_0003 | erosion and deposition by flowing water | 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 throughout the water. These particles are not dissolved in the water. Somewhat bigger particles, such as sand, are moved by saltation. The particles move in little jumps near the stream bottom. They are nudged along by water and other particles. The biggest particles, including gravel and pebbles, are moved by traction. In this process, the particles roll or drag along the bottom of the water. | text | null |
L_0003 | erosion and deposition by flowing water | 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. | text | null |
L_0003 | erosion and deposition by flowing water | T_0025 | Water that flows over Earths surface includes runoff, streams, and rivers. All these types of flowing water can cause erosion and deposition. | text | null |
L_0003 | erosion and deposition by flowing water | 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 cause more erosion if the land is bare. Plants help hold the soil in place. The runoff water in Figure 10.3 is brown because it eroded soil from a bare, sloping field. Can you find evidence of erosion by runoff where you live? What should you look for? Much of the material eroded by runoff is carried into bodies of water, such as streams, rivers, ponds, lakes, or oceans. Runoff is an important cause of erosion. Thats because it occurs over so much of Earths surface. | text | null |
L_0003 | erosion and deposition by flowing water | 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, V-shaped channel. | text | null |
L_0003 | erosion and deposition by flowing water | 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, V-shaped channel. | text | null |
L_0003 | erosion and deposition by flowing water | 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 gradually moves upstream. | text | null |
L_0003 | erosion and deposition by flowing water | 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 from side to side, they create a floodplain. This is a broad, flat area on both sides of a river. Eventually, a meander may become cut off from the rest of the river. This forms an oxbow lake, like the one in Figure 10.6. | text | null |
L_0003 | erosion and deposition by flowing water | 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 from side to side, they create a floodplain. This is a broad, flat area on both sides of a river. Eventually, a meander may become cut off from the rest of the river. This forms an oxbow lake, like the one in Figure 10.6. | text | null |
L_0003 | erosion and deposition by flowing water | 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 stop rapidly. The deposits form an alluvial fan, like the one in Figure 10.7. Deltas Deposition also occurs when a stream or river empties into a large body of still water. In this case, a delta forms. A delta is shaped like a triangle. It spreads out into the body of water. An example is shown in Figure 10.7. | text | null |
L_0003 | erosion and deposition by flowing water | 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 good places for growing plants. For example, the Nile River in Egypt provides both water and thick sediments for raising crops in the middle of a sandy desert. Natural Levees A flooding river often forms natural levees along its banks. A levee is a raised strip of sediments deposited close to the waters edge. You can see how levees form in Figure 10.8. Levees occur because floodwaters deposit their biggest sediments first when they overflow the rivers banks. | text | null |
L_0003 | erosion and deposition by flowing water | 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. | text | null |
L_0003 | erosion and deposition by flowing water | 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 are deposited. They build up on the ceiling of the cave to create formations called stalactites. A stalactite is a pointed, icicle-like mineral deposit that forms on the ceiling of a cave. They drip to the floor of the cave and harden to form stalagmites. A stalagmite is a more rounded mineral deposit that forms on the floor of a cave (Figure 10.9). Both types of formations grow in size as water keeps dripping and more minerals are deposited. | text | null |
L_0003 | erosion and deposition by flowing water | 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. | text | null |
L_0004 | erosion and deposition by waves | 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 on a shore. They pound away at the rocks and anything else they strike. Three factors determine the size of ocean waves: 1. The speed of the wind. 2. The length of time the wind blows. 3. The distance the wind blows. The faster, longer, and farther the wind blows, the bigger the waves are. Bigger waves have more energy. | text | null |
L_0004 | erosion and deposition by waves | 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. | text | null |
L_0004 | erosion and deposition by waves | 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 leaves behind pillars of rock. | text | null |
L_0004 | erosion and deposition by waves | 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. | text | null |
L_0004 | erosion and deposition by waves | 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. | text | null |
L_0004 | erosion and deposition by waves | 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. | text | null |
L_0004 | erosion and deposition by waves | 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 again picked up by a wave that is coming in at an angle. This motion is show in Figure 10.15 and at the link below. | text | null |
L_0004 | erosion and deposition by waves | 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 these landforms in Figure 10.17. | text | null |
L_0004 | erosion and deposition by waves | 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. | text | null |
L_0004 | erosion and deposition by waves | 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 the coast like a barrier island. | text | null |
L_0004 | erosion and deposition by waves | 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 beach erosion. You can see how groins work in Figure 10.19. | text | null |
L_0006 | erosion and deposition by glaciers | 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 Figure 10.27. A continental glacier is spread out over a huge area. It may cover most of a continent. Today, continental glaciers cover most of Greenland and Antarctica. In the past, they were much more extensive. A valley glacier is long and narrow. Valley glaciers form in mountains and flow downhill through mountain river valleys. | text | null |
L_0006 | erosion and deposition by glaciers | 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. Abrasion is the process in which a glacier scrapes underlying rock. The sediments and rocks frozen in the ice at the bottom and sides of a glacier act like sandpaper. They wear away rock. They may also leave scratches and grooves that show the direction the glacier moved. | text | null |
L_0006 | erosion and deposition by glaciers | 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 glacier reached. A cirque is a rounded hollow carved in the side of a mountain by a glacier. The highest cliff of a cirque is called the headwall. An arte is a jagged ridge that remains when cirques form on opposite sides of a mountain. A low spot in an arte is called a col. A horn is a sharp peak that is left behind when glacial cirques are on at least three sides of a mountain. | text | null |
L_0006 | erosion and deposition by glaciers | 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 when they melt. Moraine is sediment deposited by a glacier. A ground moraine is a thick layer of sediments left behind by a retreating glacier. An end moraine is a low ridge of sediments deposited at the end of the glacier. It marks the greatest distance the glacier advanced. A drumlin is a long, low hill of sediments deposited by a glacier. Drumlins often occur in groups called drumlin fields. The narrow end of each drumlin points in the direction the glacier was moving when it dropped the sediments. An esker is a winding ridge of sand deposited by a stream of meltwater. Such streams flow underneath a retreating glacier. A kettle lake occurs where a chunk of ice was left behind in the sediments of a retreating glacier. When the ice melted, it left a depression. The meltwater filled it to form a lake. | text | null |
L_0008 | fossils | 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 in Figure 11.1. | text | null |
L_0008 | fossils | T_0065 | The process by which remains or traces of living things become fossils is called fossilization. Most fossils are preserved in sedimentary rocks. | text | null |
L_0008 | fossils | 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. | text | null |
L_0008 | fossils | 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. | text | null |
L_0008 | fossils | 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 casts are another way organisms can be fossilized. A mold is an imprint of an organism left in rock. The organisms remains break down completely. Rock that fills in the mold resembles the original remains. The fossil that forms in the mold is called a cast. Molds and casts usually form in sedimentary rock. With compression, an organisms remains are put under great pressure inside rock layers. This leaves behind a dark stain in the rock. You can read about them in Figure 11.3. | text | null |
L_0008 | fossils | 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 without hard parts are the least likely to be fossilized. Fossils of soft organisms, from bacteria to jellyfish, are very rare. | text | null |
L_0008 | fossils | 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. | text | null |
L_0008 | fossils | 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 Himalaya mountain range. An example is shown in the Figure 11.4. Fossils of plants are found in Antarctica. Currently, Antarctica is almost completely covered with ice. The fossil plants show that Antarctica once had a much warmer climate. | text | null |
L_0008 | fossils | 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 11.5, are common index fossils. Trilobites were widespread marine animals. They lived between 500 and 600 million years ago. Rock layers containing trilobite fossils must be that age. Different species of trilobite fossils can be used to narrow the age even more. | text | null |
L_0009 | relative ages of rocks | 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 laws below. | text | null |
L_0009 | relative ages of rocks | 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 layers must be older than layers closer to the surface. This is the law of superposition. You can see an example in Figure 11.7. | text | null |
L_0009 | relative ages of rocks | 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 layers must be older than layers closer to the surface. This is the law of superposition. You can see an example in Figure 11.7. | text | null |
L_0009 | relative ages of rocks | 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 continuity. You can clearly see the same rock layers on opposite sides of the canyon. The matching rock layers were deposited at the same time, so they are the same age. | text | null |
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