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L_0207 | inner vs. outer planets | T_1325 | The four planets farthest from the Sun are the outer planets. Figure 1.2 shows the relative sizes of the outer planets and the Sun. These planets are much larger than the inner planets and are made primarily of gases and liquids, so they are also called gas giants. The gas giants are made up primarily of hydrogen and helium, the same elements that make up most of the Sun. Astronomers think that hydrogen and helium gases comprised much of the solar system when it first formed. Since the inner planets didnt have enough mass to hold on to these light gases, their hydrogen and helium floated away into space. The Sun and the massive outer planets had enough gravity to keep hydrogen and helium from drifting away. All of the outer planets have numerous moons. They all also have planetary rings, composed of dust and other small particles that encircle the planet in a thin plane. Click image to the left or use the URL below. URL: This image shows the four outer planets and the Sun, with sizes to scale. From left to right, the outer planets are Jupiter, Saturn, Uranus, and Neptune. | text | null |
L_0208 | interior of the sun | T_1326 | Fossils are our best form of evidence about Earth history, including the history of life. Along with other geological evidence from rocks and structures, fossils even give us clues about past climates, the motions of plates, and other major geological events. Since the present is the key to the past, what we know about a type of organism that lives today can be applied to past environments. | text | null |
L_0208 | interior of the sun | T_1327 | That life on Earth has changed over time is well illustrated by the fossil record. Fossils in relatively young rocks resemble animals and plants that are living today. In general, fossils in older rocks are less similar to modern organisms. We would know very little about the organisms that came before us if there were no fossils. Modern technology has allowed scientists to reconstruct images and learn about the biology of extinct animals like dinosaurs! Click image to the left for more content. | text | null |
L_0208 | interior of the sun | T_1328 | By knowing something about the type of organism the fossil was, geologists can determine whether the region was terrestrial (on land) or marine (underwater) or even if the water was shallow or deep. The rock may give clues to whether the rate of sedimentation was slow or rapid. The amount of wear and fragmentation of a fossil allows scientists to learn about what happened to the region after the organism died; for example, whether it was exposed to wave action. | text | null |
L_0208 | interior of the sun | T_1329 | The presence of marine organisms in a rock indicates that the region where the rock was deposited was once marine. Sometimes fossils of marine organisms are found on tall mountains indicating that rocks that formed on the seabed were uplifted. | text | null |
L_0208 | interior of the sun | T_1330 | By knowing something about the climate a type of organism lives in now, geologists can use fossils to decipher the climate at the time the fossil was deposited. For example, coal beds form in tropical environments but ancient coal beds are found in Antarctica. Geologists know that at that time the climate on the Antarctic continent was much warmer. Recall from Concept Plate Tectonics that Wegener used the presence of coal beds in Antarctica as one of the lines of evidence for continental drift. | text | null |
L_0208 | interior of the sun | T_1331 | An index fossil can be used to identify a specific period of time. Organisms that make good index fossils are distinctive, widespread, and lived briefly. Their presence in a rock layer can be used to identify rocks that were deposited at that period of time over a large area. | text | null |
L_0208 | interior of the sun | T_1332 | Use this resource to answer the questions that follow. Clues to the End - Permian Extinction Click image to the left for more content. 1. Why is the paleocologists collecting samples? 2. What does he want to create from the fossil evidence? 3. How is this similar to forensic science? 4. Why is it important to understand insect feeding? 5. What has been discovered from these fossils? | text | null |
L_0211 | introduction to groundwater | T_1339 | Groundwater resides in aquifers, porous rock and sediment with water in between. Water is attracted to the soil particles, and capillary action, which describes how water moves through porous media, moves water from wet soil to dry areas. Aquifers are found at different depths. Some are just below the surface and some are found much deeper below the land surface. A region may have more than one aquifer beneath it and even most deserts are above aquifers. The source region for an aquifer beneath a desert is likely to be far away, perhaps in a mountainous area. | text | null |
L_0211 | introduction to groundwater | T_1340 | The amount of water that is available to enter groundwater in a region, called recharge, is influenced by the local climate, the slope of the land, the type of rock found at the surface, the vegetation cover, land use in the area, and water retention, which is the amount of water that remains in the ground. More water goes into the ground where there is a lot of rain, flat land, porous rock, exposed soil, and where water is not already filling the soil and rock. | text | null |
L_0211 | introduction to groundwater | T_1341 | The residence time of water in a groundwater aquifer can be from minutes to thousands of years. Groundwater is often called fossil water because it has remained in the ground for so long, often since the end of the ice ages. A diagram of groundwater flow through aquifers showing residence times. Deeper aquifers typically contain older "fossil water." Click image to the left or use the URL below. URL: | text | null |
L_0212 | intrusive and extrusive igneous rocks | T_1342 | The rate at which magma cools determines whether an igneous rock is intrusive or extrusive. The cooling rate is reflected in the rocks texture. | text | null |
L_0212 | intrusive and extrusive igneous rocks | T_1343 | Igneous rocks are called intrusive when they cool and solidify beneath the surface. Intrusive rocks form plutons and so are also called plutonic. A pluton is an igneous intrusive rock body that has cooled in the crust. When magma cools within the Earth, the cooling proceeds slowly. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Granite is the most common intrusive igneous rock (see Figure 1.1 for an example). Igneous rocks make up most of the rocks on Earth. Most igneous rocks are buried below the surface and covered with sedimentary rock, or are buried beneath the ocean water. In some places, geological processes have brought Granite is made of four minerals, all visible to the naked eye: feldspar (white), quartz (translucent), hornblende (black), and bi- otite (black, platy). igneous rocks to the surface. Figure 1.2 shows a landscape in Californias Sierra Nevada Mountains made of granite that has been raised to create mountains. Californias Sierra Nevada Mountains are intrusive igneous rock exposed at Earths surface. | text | null |
L_0212 | intrusive and extrusive igneous rocks | T_1343 | Igneous rocks are called intrusive when they cool and solidify beneath the surface. Intrusive rocks form plutons and so are also called plutonic. A pluton is an igneous intrusive rock body that has cooled in the crust. When magma cools within the Earth, the cooling proceeds slowly. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have visible crystals. Granite is the most common intrusive igneous rock (see Figure 1.1 for an example). Igneous rocks make up most of the rocks on Earth. Most igneous rocks are buried below the surface and covered with sedimentary rock, or are buried beneath the ocean water. In some places, geological processes have brought Granite is made of four minerals, all visible to the naked eye: feldspar (white), quartz (translucent), hornblende (black), and bi- otite (black, platy). igneous rocks to the surface. Figure 1.2 shows a landscape in Californias Sierra Nevada Mountains made of granite that has been raised to create mountains. Californias Sierra Nevada Mountains are intrusive igneous rock exposed at Earths surface. | text | null |
L_0212 | intrusive and extrusive igneous rocks | T_1344 | Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks (Figure 1.3). Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals (Figure 1.4). Some volcanic rocks have a different texture. The rock has large crystals set within a matrix of tiny crystals. In this Extrusive igneous rocks form after lava cools above the surface. Cooled lava forms basalt with no visible crystals. Why are there no visible crys- tals? Cooling rate and gas content create other textures (see Figure 1.5 for examples of different textures). Lavas that cool extremely rapidly may have a glassy texture. Those with many holes from gas bubbles have a vesicular texture. Different cooling rate and gas content resulted in these different textures. Click image to the left or use the URL below. URL: | text | null |
L_0212 | intrusive and extrusive igneous rocks | T_1344 | Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks (Figure 1.3). Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals (Figure 1.4). Some volcanic rocks have a different texture. The rock has large crystals set within a matrix of tiny crystals. In this Extrusive igneous rocks form after lava cools above the surface. Cooled lava forms basalt with no visible crystals. Why are there no visible crys- tals? Cooling rate and gas content create other textures (see Figure 1.5 for examples of different textures). Lavas that cool extremely rapidly may have a glassy texture. Those with many holes from gas bubbles have a vesicular texture. Different cooling rate and gas content resulted in these different textures. Click image to the left or use the URL below. URL: | text | null |
L_0212 | intrusive and extrusive igneous rocks | T_1344 | Igneous rocks are called extrusive when they cool and solidify above the surface. These rocks usually form from a volcano, so they are also called volcanic rocks (Figure 1.3). Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals (Figure 1.4). Some volcanic rocks have a different texture. The rock has large crystals set within a matrix of tiny crystals. In this Extrusive igneous rocks form after lava cools above the surface. Cooled lava forms basalt with no visible crystals. Why are there no visible crys- tals? Cooling rate and gas content create other textures (see Figure 1.5 for examples of different textures). Lavas that cool extremely rapidly may have a glassy texture. Those with many holes from gas bubbles have a vesicular texture. Different cooling rate and gas content resulted in these different textures. Click image to the left or use the URL below. URL: | text | null |
L_0213 | jupiter | T_1345 | Jupiter is enormous, the largest object in the solar system besides the Sun. Although Jupiter is over 1,300 times Earths volume, it has only 318 times the mass of Earth. Like the other gas giants, it is much less dense than Earth. Because Jupiter is so large, it reflects a lot of sunlight. Jupiter is extremely bright in the night sky; only the Moon and Venus are brighter (Figure 1.1). This brightness is all the more impressive because Jupiter is quite far from the Earth 5.20 AUs away. It takes Jupiter about 12 Earth years to orbit once around the Sun. | text | null |
L_0213 | jupiter | T_1346 | Astronauts trying to land a spaceship on the surface of Jupiter would find that there is no solid surface at all! Jupiter is made mostly of hydrogen, with some helium, and small amounts of other elements (Figure 1.2). Jupiters atmosphere is composed of hydrogen and helium. Deeper within the planet, pressure compresses the gases into a liquid. Some evidence suggests that Jupiter may have a small rocky core of heavier elements at its center. This image of Jupiter was taken by Voy- ager 2 in 1979. The colors were later enhanced to bring out more details. | text | null |
L_0213 | jupiter | T_1346 | Astronauts trying to land a spaceship on the surface of Jupiter would find that there is no solid surface at all! Jupiter is made mostly of hydrogen, with some helium, and small amounts of other elements (Figure 1.2). Jupiters atmosphere is composed of hydrogen and helium. Deeper within the planet, pressure compresses the gases into a liquid. Some evidence suggests that Jupiter may have a small rocky core of heavier elements at its center. This image of Jupiter was taken by Voy- ager 2 in 1979. The colors were later enhanced to bring out more details. | text | null |
L_0213 | jupiter | T_1347 | The upper layer of Jupiters atmosphere contains clouds of ammonia (NH3 ) in bands of different colors. These bands rotate around the planet, but also swirl around in turbulent storms. The Great Red Spot (Figure 1.3) is an enormous, oval-shaped storm found south of Jupiters equator. This storm is more than three times as wide as the entire Earth. Clouds in the storm rotate in a counterclockwise direction, making one complete turn every six days or so. The Great Red Spot has been on Jupiter for at least 300 years, since astronomers could first see the storm through telescopes. Do you think the Great Red Spot is a permanent feature on Jupiter? How could you know? This image of Jupiters Great Red Spot (upper right of image) was taken by the Voyager 1 spacecraft. The white storm just below the Great Red Spot is about the same diameter as Earth. | text | null |
L_0213 | jupiter | T_1348 | Jupiter has a very large number of moons 63 have been discovered so far. Four are big enough and bright enough to be seen from Earth, using no more than a pair of binoculars. These moons Io, Europa, Ganymede, and Callisto were first discovered by Galileo in 1610, so they are sometimes referred to as the Galilean moons (Figure 1.4). The Galilean moons are larger than the dwarf planets Pluto, Ceres, and Eris. Ganymede is not only the biggest moon in the solar system; it is even larger than the planet Mercury! Scientists are particularly interested in Europa because it may be a place to find extraterrestrial life. What features might make a satellite so far from the Sun a candidate for life? Although the surface of Europa is a smooth layer of ice, there is evidence that there is an ocean of liquid water underneath (Figure 1.5). Europa also has a continual source of energy it is heated as it is stretched and squashed by tidal forces from Jupiter. Numerous missions have been planned to explore Europa, including plans to drill through the ice and send a probe into the ocean. However, no such mission has yet been attempted. In 1979, two spacecraft Voyager 1 and Voyager 2 visited Jupiter and its moons. Photos from the Voyager missions showed that Jupiter has a ring system. This ring system is very faint, so it is difficult to observe from Earth. This composite image shows the four Galilean moons and their sizes relative to the Great Red Spot. From top to bottom, the moons are Io, Europa, Ganymede, and Callisto. Jupiters Great Red Spot is in the background. Sizes are to scale. Click image to the left or use the URL below. URL: | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1360 | Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL: Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1360 | Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL: Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1360 | Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL: Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1360 | Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL: Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1360 | Glaciers erode the underlying rock by abrasion and plucking. Glacial meltwater seeps into cracks of the underlying rock. When the water freezes, it pushes pieces of rock outward. The rock is then plucked out and carried away by the flowing ice of the moving glacier (Figure 1.1). With the weight of the ice over them, these rocks can scratch deeply into the underlying bedrock, making long, parallel grooves in the bedrock, called glacial striations. Mountain glaciers leave behind unique erosional features. When a glacier cuts through a V-shaped river valley, the glacier plucks rocks from the sides and bottom. This widens the valley and steepens the walls, making a U-shaped valley (Figure 1.2). Smaller tributary glaciers, like tributary streams, flow into the main glacier in their own shallower U-shaped valleys. A hanging valley forms where the main glacier cuts off a tributary glacier and creates a cliff. Streams plunge over the cliff to create waterfalls (Figure 1.3). Up high on a mountain, where a glacier originates, rocks are pulled away from valley walls. Some of the resulting erosional features are shown in Figure 1.4 and Figure 1.5. Glacial striations point the direction a glacier has gone. A U-shaped valley in Glacier National Park. Click image to the left or use the URL below. URL: Yosemite Valley is known for waterfalls that plunge from hanging valleys. (a) A bowl-shaped cirque in Glacier Na- tional Park was carved by glaciers. (b) A high altitude lake, called a tarn, forms from meltwater trapped in the cirque. (c) Several cirques from glaciers flowing in different directions from a mountain peak, leave behind a sharp sided horn, like the Matterhorn in Switzerland. (d) When glaciers move down opposite sides of a mountain, a sharp edged ridge, called an arte, forms between them. Snowmelt and melting glaciers combine to create a fast moving stream at Glacier National Park. | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1361 | As glaciers flow, mechanical weathering loosens rock on the valley walls, which falls as debris on the glacier. Glaciers can carry rock of any size, from giant boulders to silt (Figure 1.6). These rocks can be carried for many kilometers for many years. | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1362 | Rocks carried by a glacier are eventually dropped. These glacial erratics are noticeable because they are a different rock type from the surrounding bedrock. | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1363 | Melting glaciers deposit all the big and small bits of rocky material they are carrying in a pile. These unsorted deposits of rock are called glacial till. Glacial till is found in different types of deposits. Linear rock deposits are called moraines. Geologists study moraines to figure out how far glaciers extended and how long it took them to melt away. Moraines are named by their location relative to the glacier: Lateral moraines form at the edges of the glacier as material drops onto the glacier from erosion of the valley walls. Medial moraines form where the lateral moraines of two tributary glaciers join together in the middle of a larger glacier (Figure 1.7). Ground moraines forms from sediments that were beneath the glacier and left behind after the glacier melts. Ground moraine sediments contribute to the fertile transported soils in many regions. Terminal moraines are long ridges of till left at the furthest point the glacier reached. End moraines are deposited where the glacier stopped for a long enough period to create a rocky ridge as it retreated. Long Island in New York is formed by two end moraines. | text | null |
L_0215 | landforms from glacial erosion and deposition | T_1364 | Several types of stratified deposits form in glacial regions but are not formed directly by the ice. Varves form where lakes are covered by ice in the winter. Dark, fine-grained clays sink to the bottom in winter, but melting ice in spring brings running water that deposits lighter colored sands. Each alternating dark/light layer represents one year of deposits. (a) An esker is a winding ridge of sand and gravel deposited under a glacier by a stream of meltwater. (b) A drumlin is an asymmetrical hill made of sediments that points in the direction the ice moved. Usually drumlins are found in groups called drumlin fields. Click image to the left or use the URL below. URL: | text | null |
L_0216 | landforms from groundwater erosion and deposition | T_1365 | Rainwater absorbs carbon dioxide (CO2 ) as it falls. The CO2 combines with water to form carbonic acid. The slightly acidic water sinks into the ground and moves through pore spaces in soil and cracks and fractures in rock. The flow of water underground is groundwater. Groundwater is described further in the chapter Water on Earth. Groundwater is a strong erosional force, as it works to dissolve away solid rock (Figure 1.1). Carbonic acid is especially good at dissolving the rock limestone. | text | null |
L_0216 | landforms from groundwater erosion and deposition | T_1366 | Working slowly over many years, groundwater travels along small cracks. The water dissolves and carries away the solid rock, gradually enlarging the cracks. Eventually, a cave may form (Figure 1.2). | text | null |
L_0216 | landforms from groundwater erosion and deposition | T_1367 | If the roof of a cave collapses, a sinkhole could form. Some sinkholes are large enough to swallow up a home or several homes in a neighborhood (Figure 1.3). Water flows through Russell Cave Na- tional Monument in Alabama. | text | null |
L_0216 | landforms from groundwater erosion and deposition | T_1367 | If the roof of a cave collapses, a sinkhole could form. Some sinkholes are large enough to swallow up a home or several homes in a neighborhood (Figure 1.3). Water flows through Russell Cave Na- tional Monument in Alabama. | text | null |
L_0216 | landforms from groundwater erosion and deposition | T_1368 | Groundwater carries dissolved minerals in solution. The minerals may then be deposited, for example, as stalag- mites or stalactites (Figure 1.4). Stalactites form as calcium carbonate drips from the ceiling of a cave, forming beautiful icicle-like formations. The word stalactite has a c, and it forms from the ceiling. Stalagmites form as calcium carbonate drips from the ceiling to the floor of a cave and then grow upwards. The g in stalagmite means it forms on the ground. If a stalactite and stalagmite join together, they form a column. One of the wonders of visiting a cave is to witness the beauty of these amazing and strangely captivating structures. Some of the largest, and most beautiful, natural crystals can be found in the Naica mine, in Mexico. These gypsum crystals were formed over thousands of years as groundwater, rich in calcium and sulfur flowed through an underground cave. Check it out: A relatively small sinkhole in a Georgia parking lot. Stalactites hang from the ceiling and stalagmites rise from the floor of Carlsbad Caverns in New Mexico. The large stalagmite on the right is almost tall enough to reach the ceiling (or a stalactite) and form a column. Click image to the left or use the URL below. URL: | text | null |
L_0216 | landforms from groundwater erosion and deposition | T_1368 | Groundwater carries dissolved minerals in solution. The minerals may then be deposited, for example, as stalag- mites or stalactites (Figure 1.4). Stalactites form as calcium carbonate drips from the ceiling of a cave, forming beautiful icicle-like formations. The word stalactite has a c, and it forms from the ceiling. Stalagmites form as calcium carbonate drips from the ceiling to the floor of a cave and then grow upwards. The g in stalagmite means it forms on the ground. If a stalactite and stalagmite join together, they form a column. One of the wonders of visiting a cave is to witness the beauty of these amazing and strangely captivating structures. Some of the largest, and most beautiful, natural crystals can be found in the Naica mine, in Mexico. These gypsum crystals were formed over thousands of years as groundwater, rich in calcium and sulfur flowed through an underground cave. Check it out: A relatively small sinkhole in a Georgia parking lot. Stalactites hang from the ceiling and stalagmites rise from the floor of Carlsbad Caverns in New Mexico. The large stalagmite on the right is almost tall enough to reach the ceiling (or a stalactite) and form a column. Click image to the left or use the URL below. URL: | text | null |
L_0217 | lithification of sedimentary rocks | T_1369 | Accumulated sediments harden into rock by lithification, as illustrated in the Figure 1.1. Two important steps are needed for sediments to lithify. 1. Sediments are squeezed together by the weight of overlying sediments on top of them. This is called com- paction. Cemented, non-organic sediments become clastic rocks. If organic material is included, they are bioclastic rocks. 2. Fluids fill in the spaces between the loose particles of sediment and crystallize to create a rock by cementation. The sediment size in clastic sedimentary rocks varies greatly (see Table in Sedimentary Rocks Classification). This cliff is made of sandstone. Sands were deposited and then lithified. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0221 | location and direction | T_1381 | How would you find Old Faithful? One way is by using latitude and longitude. Any location on Earths surface or on a map can be described using these coordinates. Latitude and longitude are expressed as degrees that are divided into 60 minutes. Each minute is divided into 60 seconds. | text | null |
L_0221 | location and direction | T_1382 | A look on a reliable website shows us that Old Faithful Geyser is located at N44o 27 43. What does this mean? Latitude tells the distance north or south of the Equator. Latitude lines start at the Equator and circle around the planet. The North Pole is 90o N, with 90 degree lines in the Northern Hemisphere. Old Faithful is at 44 degrees, 27 minutes and 43 seconds north of the Equator. Thats just about exactly half way between the Equator and the North Pole! | text | null |
L_0221 | location and direction | T_1383 | The latitude mentioned above does not locate Old Faithful exactly, since a circle could be drawn that latitude north of the Equator. To locate Old Faithful we need another point - longitude. At Old Faithful the longitude is W110o 4957. Longitude lines are circles that go around the Earth from north to south, like the sections of an orange. Longitude is measured perpendicular to the Equator. The Prime Meridian is 0o longitude and passes through Greenwich, England. The International Date Line is the 180o meridian. Old Faithful is in the Western Hemisphere, between the Prime Meridian in the east and the International Date Line in the west. | text | null |
L_0221 | location and direction | T_1384 | An accurate location must take into account the third dimension. Elevation is the height above or below sea level. Sea level is the average height of the oceans surface or the midpoint between high and low tide. Sea level is the same all around Earth. Old Faithful is higher above sea level than most locations at 7,349 ft (2240 m). Of course, the highest point on Earth, Mount Everest, is much higher at 29,029 ft (8848 m). | text | null |
L_0221 | location and direction | T_1385 | Satellites continually orbit Earth and can be used to indicate location. A global positioning system receiver detects radio signals from at least four nearby GPS satellites. The receiver measures the time it takes for radio signals to travel from a satellite and then calculates its distance from the satellite using the speed of radio signals. By calculating distances from each of the four satellites the receiver can triangulate to determine its location. You can use a GPS meter to tell you how to get to Old Faithful. | text | null |
L_0221 | location and direction | T_1386 | Direction is important if you want to go between two places. Directions are expressed as north (N), east (E), south (S), and west (W), with gradations in between. The most common way to describe direction in relation to the Earths surface is with a compass, a device with a floating needle that is actually a small magnet. The compass needle aligns itself with the Earths magnetic north pole. Since the magnetic north pole is 11.5 degrees offset from its geographic north pole on the axis of rotation, you must correct for this discrepancy. Map of the Visitor Center at Old Faithful, Yellowstone National Park, Wyoming. Without using a compass, we can say that to get to Old Faithful, you enter Yellowstone National Park at the South Entrance, drive north-northeast to West Thumb, and then drive west-northwest to Old Faithful. Click image to the left or use the URL below. URL: | text | null |
L_0222 | long term climate change | T_1387 | Many processes can cause climate to change. These include changes: In the amount of energy the Sun produces over years. In the positions of the continents over millions of years. In the tilt of Earths axis and orbit over thousands of years. That are sudden and dramatic because of random catastrophic events, such as a large asteroid impact. In greenhouse gases in the atmosphere, caused naturally or by human activities. | text | null |
L_0222 | long term climate change | T_1388 | The amount of energy the Sun radiates is variable. Sunspots are magnetic storms on the Suns surface that increase and decrease over an 11-year cycle (Figure 1.1). When the number of sunspots is high, solar radiation is also relatively high. But the entire variation in solar radiation is tiny relative to the total amount of solar radiation that there is, and there is no known 11-year cycle in climate variability. The Little Ice Age corresponded to a time when there were no sunspots on the Sun. Sunspots on the face of the Sun. | text | null |
L_0222 | long term climate change | T_1389 | Plate tectonic movements can alter climate. Over millions of years as seas open and close, ocean currents may distribute heat differently. For example, when all the continents are joined into one supercontinent (such as Pangaea), nearly all locations experience a continental climate. When the continents separate, heat is more evenly distributed. Plate tectonic movements may help start an ice age. When continents are located near the poles, ice can accumulate, which may increase albedo and lower global temperature. Low enough temperatures may start a global ice age. Plate motions trigger volcanic eruptions, which release dust and CO2 into the atmosphere. Ordinary eruptions, even large ones, have only a short-term effect on weather (Figure 1.2). Massive eruptions of the fluid lavas that create lava plateaus release much more gas and dust, and can change climate for many years. This type of eruption is exceedingly rare; none has occurred since humans have lived on Earth. | text | null |
L_0222 | long term climate change | T_1390 | The most extreme climate of recent Earth history was the Pleistocene. Scientists attribute a series of ice ages to variation in the Earths position relative to the Sun, known as Milankovitch cycles. The Earth goes through regular variations in its position relative to the Sun: 1. The shape of the Earths orbit changes slightly as it goes around the Sun. The orbit varies from more circular to more elliptical in a cycle lasting between 90,000 and 100,000 years. When the orbit is more elliptical, there is a greater difference in solar radiation between winter and summer. 2. The planet wobbles on its axis of rotation. At one extreme of this 27,000 year cycle, the Northern Hemisphere points toward the Sun when the Earth is closest to the Sun. Summers are much warmer and winters are much colder than now. At the opposite extreme, the Northern Hemisphere points toward the Sun when it is farthest from the Sun. An eruption like Sarychev Volcano (Kuril Islands, northeast of Japan) in 2009 would have very little impact on weather. This results in chilly summers and warmer winters. 3. The planets tilt on its axis varies between 22.1o and 24.5o . Seasons are caused by the tilt of Earths axis of rotation, which is at a 23.5o angle now. When the tilt angle is smaller, summers and winters differ less in temperature. This cycle lasts 41,000 years. When these three variations are charted out, a climate pattern of about 100,000 years emerges. Ice ages correspond closely with Milankovitch cycles. Since glaciers can form only over land, ice ages only occur when landmasses cover the polar regions. Therefore, Milankovitch cycles are also connected to plate tectonics. | text | null |
L_0222 | long term climate change | T_1391 | Since greenhouse gases trap the heat that radiates off the planets surfaces, what would happen to global temperatures if atmospheric greenhouse gas levels decreased? What if greenhouse gases increased? A decrease in greenhouse gas levels decreases global temperature and an increase raises global temperature. Greenhouse gas levels have varied throughout Earth history. For example, CO2 has been present at concentrations less than 200 parts per million (ppm) and more than 5,000 ppm. But for at least 650,000 years, CO2 has never risen above 300 ppm, during either glacial or interglacial periods (Figure 1.3). Natural processes add and remove CO2 from the atmosphere. Processes that add CO2 : volcanic eruptions decay or burning of organic matter. Processes that remove CO2 : absorption by plant and animal tissue. When plants are turned into fossil fuels, the CO2 in their tissue is stored with them. So CO2 is removed from the atmosphere. What does this do to Earths average temperature? What happens to atmospheric CO2 when the fossil fuels are burned? What happens to global temperatures? CO2 levels during glacial (blue) and inter- glacial (yellow) periods. Are CO2 levels relatively high or relatively low during in- terglacial periods? Current carbon diox- ide levels are at around 400 ppm, the highest level for the last 650,000 years. BP means years before present. | text | null |
L_0224 | magnetic evidence for seafloor spreading | T_1393 | On our transit to the Mid-Atlantic ridge, we tow a magnetometer behind the ship. Shipboard magnetometers reveal the magnetic polarity of the rock beneath them. The practice of towing a magnetometer began during WWII when navy ships towed magnetometers to search for enemy submarines. When scientists plotted the points of normal and reversed polarity on a seafloor map they made an astonishing discovery: the normal and reversed magnetic polarity of seafloor basalts creates a pattern. Stripes of normal polarity and reversed polarity alternate across the ocean bottom. Stripes form mirror images on either side of the mid-ocean ridges (Figure 1.1). Stripes end abruptly at the edges of continents, sometimes at a deep sea trench (Figure 1.2). The magnetic stripes are what created the Figure 1.1. Research cruises today tow magnetometers to add detail to existing magnetic polarity data. | text | null |
L_0224 | magnetic evidence for seafloor spreading | T_1394 | By combining magnetic polarity data from rocks on land and on the seafloor with radiometric age dating and fossil ages, scientists came up with a time scale for the magnetic reversals. The first four magnetic periods are: Brunhes normal - present to 730,000 years ago. Matuyama reverse - 730,000 years ago to 2.48 million years ago. Gauss normal - 2.48 to 3.4 million years ago. Gilbert reverse - 3.4 to 5.3 million years ago. The scientists noticed that the rocks got older with distance from the mid-ocean ridges. The youngest rocks were located at the ridge crest and the oldest rocks were located the farthest away, abutting continents. Scientists also noticed that the characteristics of the rocks and sediments changed with distance from the ridge axis as seen in the Table 1.1. Rock ages At ridge axis With distance from axis youngest becomes older Sediment thickness none becomes thicker Crust thickness Heat flow thinnest becomes thicker hottest becomes cooler Away from the ridge crest, sediment becomes older and thicker, and the seafloor becomes thicker. Heat flow, which indicates the warmth of a region, is highest at the ridge crest. The oldest seafloor is near the edges of continents or deep sea trenches and is less than 180 million years old (Figure something was happening to the older seafloor. Seafloor is youngest at the mid-ocean ridges and becomes progressively older with distance from the ridge. How can you explain the observations that scientists have made in the oceans? Why is rock younger at the ridge and oldest at the farthest points from the ridge? The scientists suggested that seafloor was being created at the ridge. Since the planet is not getting larger, they suggested that it is destroyed in a relatively short amount of geologic time. Click image to the left or use the URL below. URL: | text | null |
L_0225 | magnetic polarity evidence for continental drift | T_1395 | The next breakthrough in the development of the theory of plate tectonics came two decades after Wegeners death. Magnetite crystals are shaped like a tiny bar magnet. As basalt lava cools, the magnetite crystals line up in the magnetic field like tiny magnets. When the lava is completely cooled, the crystals point in the direction of magnetic north pole at the time they form. How do you expect this would help scientists see whether continents had moved or not? As a Wegener supporter, (and someone who is omniscient), you have just learned of a new tool that may help you. A magnetometer is a device capable of measuring the magnetic field intensity. This allows you to look at the magnetic properties of rocks in many locations. First, youre going to look at rocks on land. Which rocks should you seek out for study? | text | null |
L_0225 | magnetic polarity evidence for continental drift | T_1396 | Geologists noted important things about the magnetic polarity of different aged rocks on the same continent: Magnetite crystals in fresh volcanic rocks point to the current magnetic north pole (Figure 1.2) no matter what continent or where on the continent the rocks are located. Older rocks that are the same age and are located on the same continent point to the same location, but that location is not the current north magnetic pole. Older rocks that are of different ages do not point to the same locations or to the current magnetic north pole. In other words, although the magnetite crystals were pointing to the magnetic north pole, the location of the pole seemed to wander. Scientists were amazed to find that the north magnetic pole changed location over time (Figure Can you figure out the three possible explanations for this? They are: The location of the north magnetic north pole 80 million years before present (mybp), then 60, 40, 20, and now. 1. The continents remained fixed and the north magnetic pole moved. 2. The north magnetic pole stood still and the continents moved. 3. Both the continents and the north pole moved. | text | null |
L_0225 | magnetic polarity evidence for continental drift | T_1396 | Geologists noted important things about the magnetic polarity of different aged rocks on the same continent: Magnetite crystals in fresh volcanic rocks point to the current magnetic north pole (Figure 1.2) no matter what continent or where on the continent the rocks are located. Older rocks that are the same age and are located on the same continent point to the same location, but that location is not the current north magnetic pole. Older rocks that are of different ages do not point to the same locations or to the current magnetic north pole. In other words, although the magnetite crystals were pointing to the magnetic north pole, the location of the pole seemed to wander. Scientists were amazed to find that the north magnetic pole changed location over time (Figure Can you figure out the three possible explanations for this? They are: The location of the north magnetic north pole 80 million years before present (mybp), then 60, 40, 20, and now. 1. The continents remained fixed and the north magnetic pole moved. 2. The north magnetic pole stood still and the continents moved. 3. Both the continents and the north pole moved. | text | null |
L_0225 | magnetic polarity evidence for continental drift | T_1397 | How do you figure out which of those three possibilities is correct? You decide to look at magnetic rocks on different continents. Geologists noted that for rocks of the same age but on different continents, the little magnets pointed to different magnetic north poles. 400 million-year-old magnetite in Europe pointed to a different north magnetic pole than magnetite of the same age in North America. 250 million years ago, the north poles were also different for the two continents. Now look again at the three possible explanations. Only one can be correct. If the continents had remained fixed while the north magnetic pole moved, there must have been two separate north poles. Since there is only one north pole today, what is the best explanation? The only reasonable explanation is that the magnetic north pole has remained fixed but that the continents have moved. | text | null |
L_0225 | magnetic polarity evidence for continental drift | T_1398 | How does this help you to provide evidence for continental drift? To test the idea that the pole remained fixed but the continents moved, geologists fitted the continents together as Wegener had done. It worked! There has only been one magnetic north pole and the continents have drifted (Figure 1.4). They named the phenomenon of the magnetic pole that seemed to move but actually did not apparent polar wander. On the left: The apparent north pole for Europe and North America if the continents were always in their current locations. The two paths merge into one if the continents are allowed to drift. This evidence for continental drift gave geologists renewed interest in understanding how continents could move about on the planets surface. | text | null |
L_0226 | maps | T_1399 | Topographic maps represent the locations of geographical features, such as hills and valleys. Topographic maps use contour lines to show different elevations. A contour line is a line of equal elevation. If you walk along a contour line you will not go uphill or downhill. Topographic maps are also called contour maps. The rules of topographic maps are: Each line connects all points of a specific elevation. Contour lines never cross since a single point can only have one elevation. Every fifth contour line is bolded and labeled. Adjacent contour lines are separated by a constant difference in elevation (such as 20 ft or 100 ft). The difference in elevation is the contour interval, which is indicated in the map legend. Scales indicate horizontal distance and are also found on the map legend. Old Faithful erupting, Yellowstone Na- tional Park. While the Figure 1.1 isnt exactly the same view as the map at the top of this concept, it is easy to see the main features. Hills, forests, development, and trees are all seen around Old Faithful. | text | null |
L_0226 | maps | T_1400 | A bathymetric map is like a topographic map with the contour lines representing depth below sea level, rather than height above. Numbers are low near sea level and become higher with depth. Kilauea is the youngest volcano found above sea level in Hawaii. On the flank of Kilauea is an even younger volcano called Loihi. The bathymetric map pictured in the Figure 1.2 shows the form of Loihi. Loihi volcano growing on the flank of Kilauea volcano in Hawaii. Black lines in the inset show the land surface above sea level and blue lines show the topography below sea level. A geologic map of the region around Old Faithful, Yellowstone National Park. | text | null |
L_0226 | maps | T_1400 | A bathymetric map is like a topographic map with the contour lines representing depth below sea level, rather than height above. Numbers are low near sea level and become higher with depth. Kilauea is the youngest volcano found above sea level in Hawaii. On the flank of Kilauea is an even younger volcano called Loihi. The bathymetric map pictured in the Figure 1.2 shows the form of Loihi. Loihi volcano growing on the flank of Kilauea volcano in Hawaii. Black lines in the inset show the land surface above sea level and blue lines show the topography below sea level. A geologic map of the region around Old Faithful, Yellowstone National Park. | text | null |
L_0226 | maps | T_1401 | A geologic map shows the geological features of a region (see Figure 1.3 for an example). Rock units are color- coded and identified in a key. Faults and folds are also shown on geologic maps. The geology is superimposed on a topographic map to give a more complete view of the geology of the region. Click image to the left or use the URL below. URL: | text | null |
L_0227 | mars | T_1402 | Mars is the fourth planet from the Sun, and the first planet beyond Earths orbit (Figure 1.1). Mars is a quite different from Earth and yet more similar than any other planet. Mars is smaller, colder, drier, and appears to have no life, but volcanoes are common to both planets and Mars has many. Mars is easy to observe, so Mars has been studied more thoroughly than any other extraterrestrial planet. Space probes, rovers, and orbiting satellites have all yielded information to planetary geologists. Although no humans have ever set foot on Mars, both NASA and the European Space Agency have set goals of sending people to Mars sometime between 2030 and 2040. This image of Mars, taken by the Hubble Space Telescope in October, 2005, shows the planets red color, a small ice cap on the south pole, and a dust storm. | text | null |
L_0227 | mars | T_1403 | Viewed from Earth, Mars is reddish in color. The ancient Greeks and Romans named the planet after the god of war. The surface is not red from blood but from large amounts of iron oxide in the soil. The Martian atmosphere is very thin relative to Earths and has much lower atmospheric pressure. Although the atmosphere is made up mostly of carbon dioxide, the planet has only a weak greenhouse effect, so temperatures are only slightly higher than if the planet had no atmosphere. | text | null |
L_0227 | mars | T_1404 | Mars has mountains, canyons, and other features similar to Earth. Some of these surface features are amazing for their size! Olympus Mons is a shield volcano, similar to the volcanoes that make up the Hawaiian Islands. But Olympus Mons is also the largest mountain in the solar system (Figure 1.2). Mars also has the largest canyon in the solar system, Valles Marineris (Figure 1.3). | text | null |
L_0227 | mars | T_1405 | It was previously believed that water cannot stay in liquid form on Mars because the atmospheric pressure is too low. However, there is a lot of water in the form of ice and even prominent ice caps (Figure 1.4). Scientists also think Olympus Mons is about 27 km (16.7 miles/88,580 ft) above the Martian sur- face, more than three times taller than Mount Everest. The volcanos base is about the size of the state of Arizona. Valles Marineris is 4,000 km (2,500 mi) long, as long as Europe is wide, and one-fifth the circumference of Mars. The canyon is 7 km (4.3 mi) deep. By comparison, the Grand Canyon on Earth is only 446 km (277 mi) long and about 2 km (1.2 mi) deep. that there is a lot of ice present just under the Martian surface. This ice can melt when volcanoes erupt, and water can flow across the surface. In late 2015, NASA confirmed the presence of water on Mars. Scientists think that water once flowed over the Martian surface because there are surface features that look like water-eroded canyons. The presence of water on Mars suggests that it might have been possible for life to exist on Mars in the past. | text | null |
L_0227 | mars | T_1405 | It was previously believed that water cannot stay in liquid form on Mars because the atmospheric pressure is too low. However, there is a lot of water in the form of ice and even prominent ice caps (Figure 1.4). Scientists also think Olympus Mons is about 27 km (16.7 miles/88,580 ft) above the Martian sur- face, more than three times taller than Mount Everest. The volcanos base is about the size of the state of Arizona. Valles Marineris is 4,000 km (2,500 mi) long, as long as Europe is wide, and one-fifth the circumference of Mars. The canyon is 7 km (4.3 mi) deep. By comparison, the Grand Canyon on Earth is only 446 km (277 mi) long and about 2 km (1.2 mi) deep. that there is a lot of ice present just under the Martian surface. This ice can melt when volcanoes erupt, and water can flow across the surface. In late 2015, NASA confirmed the presence of water on Mars. Scientists think that water once flowed over the Martian surface because there are surface features that look like water-eroded canyons. The presence of water on Mars suggests that it might have been possible for life to exist on Mars in the past. | text | null |
L_0227 | mars | T_1405 | It was previously believed that water cannot stay in liquid form on Mars because the atmospheric pressure is too low. However, there is a lot of water in the form of ice and even prominent ice caps (Figure 1.4). Scientists also think Olympus Mons is about 27 km (16.7 miles/88,580 ft) above the Martian sur- face, more than three times taller than Mount Everest. The volcanos base is about the size of the state of Arizona. Valles Marineris is 4,000 km (2,500 mi) long, as long as Europe is wide, and one-fifth the circumference of Mars. The canyon is 7 km (4.3 mi) deep. By comparison, the Grand Canyon on Earth is only 446 km (277 mi) long and about 2 km (1.2 mi) deep. that there is a lot of ice present just under the Martian surface. This ice can melt when volcanoes erupt, and water can flow across the surface. In late 2015, NASA confirmed the presence of water on Mars. Scientists think that water once flowed over the Martian surface because there are surface features that look like water-eroded canyons. The presence of water on Mars suggests that it might have been possible for life to exist on Mars in the past. | text | null |
L_0227 | mars | T_1406 | Mars has two very small moons that are irregular rocky bodies (Figure 1.5). Phobos and Deimos are named after characters in Greek mythology the two sons of Ares, who followed their father into war. Ares is equivalent to the Roman god Mars. Mars has two small moons, Phobos (left) and Deimos (right). Both were discovered in 1877 and are thought to be captured asteroids. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0229 | measuring earthquake magnitude | T_1408 | A seismograph produces a graph-like representation of the seismic waves it receives and records them onto a seismogram (Figure 1.1). Seismograms contain information that can be used to determine how strong an earthquake was, how long it lasted, and how far away it was. Modern seismometers record ground motions using electronic motion detectors. The data are then kept digitally on a computer. If a seismogram records P-waves and surface waves but not S-waves, the seismograph was on the other side of the Earth from the earthquake. The amplitude of the waves can be used to determine the magnitude of the earthquake, which will be discussed in a later section. | text | null |
L_0229 | measuring earthquake magnitude | T_1409 | The seismogram in the introduction shows: foreshocks. the arrival of the P-waves. the arrival of the S-waves. the arrival of the surface waves (very hard to pick out). aftershocks. the times when all of these things occur. These seismograms show the arrival of P- waves and S-waves. The surface waves arrive just after the S-waves and are diffi- cult to distinguish. Time is indicated on the horizontal portion (or x-axis) of the graph. Click image to the left or use the URL below. URL: | text | null |
L_0230 | mechanical weathering | T_1410 | Mechanical weathering (also called physical weathering) breaks rock into smaller pieces. These smaller pieces are just like the bigger rock, but smaller. That means the rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock. | text | null |
L_0230 | mechanical weathering | T_1411 | There are many ways that rocks can be broken apart into smaller pieces. Ice wedging is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point (Figure 1.1). Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons. Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside, as rock fragments separate and tumble down. Ice wedging is common in Earths polar regions and mid latitudes, and also at higher elevations, such as in the mountains. | text | null |
L_0230 | mechanical weathering | T_1412 | Abrasion is another form of mechanical weathering. In abrasion, one rock bumps against another rock. Gravity causes abrasion as a rock tumbles down a mountainside or cliff. Moving water causes abrasion as particles in the water collide and bump against one another. Strong winds carrying pieces of sand can sandblast surfaces. Ice in glaciers carries many bits and pieces of rock. Rocks embedded at the bottom of the glacier scrape against the rocks below. Abrasion makes rocks with sharp or jagged edges smooth and round. If you have ever collected beach glass or cobbles from a stream, you have witnessed the work of abrasion (Figure 1.2). | text | null |
L_0230 | mechanical weathering | T_1413 | Now that you know what mechanical weathering is, can you think of other ways it could happen? Plants and animals can do the work of mechanical weathering (Figure 1.3). This could happen slowly as a plants roots grow into a crack or fracture in rock and gradually grow larger, wedging open the crack. Burrowing animals can also break apart rock as they dig for food or to make living spaces for themselves. | text | null |
L_0230 | mechanical weathering | T_1414 | Human activities are responsible for enormous amounts of mechanical weathering, by digging or blasting into rock to build homes, roads, and subways, or to quarry stone. (a) Humans are tremendous agents of mechanical weathering. (b) Salt weathering of building stone on the island of Gozo, Malta. | text | null |
L_0231 | mercury | T_1415 | The smallest planet, Mercury, is the planet closest to the Sun. Because Mercury is so close to the Sun, it is difficult to observe from Earth, even with a telescope. However, the Mariner 10 spacecraft, shown in Figure 1.1, visited Mercury from 1974 to 1975. The MESSENGER spacecraft has been studying Mercury in detail since 2005. The craft is currently in orbit around the planet, where it is creating detailed maps. MESSENGER stands for Mercury Surface, Space Environment, Geochemistry and Ranging. (a) Mariner 10 made three flybys of Mercury in 1974 and 1975. (b) A 2008 image of compiled from a flyby by MESSENGER. As Figure 1.2 shows, the surface of Mercury is covered with craters, like Earths Moon. Ancient impact craters means that for billions of years Mercury hasnt changed much geologically. Also, with very little atmosphere, the processes of weathering and erosion do not wear down structures on the planet. | text | null |
L_0231 | mercury | T_1416 | Mercury is named for the Roman messenger god, who could run extremely quickly, just as the planet moves very quickly in its orbit around the Sun. A year on Mercury the length of time it takes to orbit the Sun is just 88 Earth days. Despite its very short years, Mercury has very long days. A day is defined as the time it takes a planet to turn on its axis. Mercury rotates slowly on its axis, turning exactly three times for every two times it orbits the Sun. Therefore, each day on Mercury is 57 Earth days long. In other words, on Mercury, a year is only a Mercury day and a half long! | text | null |
L_0231 | mercury | T_1417 | Mercury is close to the Sun, so it can get very hot. However, Mercury has virtually no atmosphere, no water to insulate the surface, and it rotates very slowly. For these reasons, temperatures on the surface of Mercury vary widely. In direct sunlight, the surface can be as hot as 427 C (801 F). On the dark side, or in the shadows inside craters, the surface can be as cold as -183 C (-297 F)! Although most of Mercury is extremely dry, scientists think Mercury is covered with craters, like Earths Moon. MESSENGER has taken extremely detailed pictures of the planets surface. there may be a small amount of water in the form of ice at the poles of Mercury, in areas that never receive direct sunlight. | text | null |
L_0231 | mercury | T_1418 | Figure 1.3 shows a diagram of Mercurys interior. Mercury is one of the densest planets. Its relatively large, liquid core, made mostly of melted iron, takes up about 42% of the planets volume. | text | null |
L_0232 | mercury pollution | T_1419 | Mercury is released into the atmosphere when coal is burned (Figure 1.1). But breathing the mercury is not harmful. In the atmosphere, the mercury forms small droplets that are deposited in water or sediments. | text | null |
L_0232 | mercury pollution | T_1420 | Do you know why you are supposed to eat large predatory fish like tuna infrequently? It is because of the bioaccu- mulation of mercury in those species. Some pollutants remain in an organism throughout its life, a phenomenon called bioaccumulation. In this process, an organism accumulates the entire amount of a toxic compound that it consumes over its lifetime. Not all substances bioaccumulate. Can you name one that does not? Aspirin does not bioaccumulate; if it did, a person would quickly accumulate a toxic amount in her body. Compounds that bioaccumulate are usually stored in the organisms fat. In the sediments, bacteria convert the droplets to the hazardous compound methyl mercury. Bacteria and plankton store all of the mercury from all of the seawater they ingest (Figure 1.2). A small fish that eats bacteria and plankton accumulates all of the mercury from all of the tiny creatures it eats over its lifetime. A big fish accumulates all of the mercury from all of the small fish it eats over its lifetime. For a tuna at the top of the food chain, thats a lot of mercury. Historic increases of mercury in the atmo- sphere: blue is volcanic eruptions; brown, purple, and pink are human-caused. The red region shows the effect of industrial- ization on atmospheric mercury. So tuna pose a health hazard to anything that eats them because their bodies are so high in mercury. This is why the government recommends limits on the amount of tuna that people eat. Limiting intake of large predatory fish is especially important for children and pregnant women. If the mercury just stayed in a persons fat, it would not be harmful, but that fat is used when a woman is pregnant or nursing a baby. A person will also get the mercury into her system when she (or he) burns the fat while losing weight. | text | null |
L_0232 | mercury pollution | T_1421 | Methyl mercury poisoning can cause nervous system or brain damage, especially in infants and children. Children may experience brain damage or developmental delays. The phrase mad as a hatter was common when Lewis Carroll wrote his Alice in Wonderland stories. It was based on symptoms suffered by hatters who were exposed to mercury and experienced mercury poisoning while using the metal to make hats (Figure 1.3). Like mercury, other metals and VOCS can bioaccumulate, causing harm to animals and people high on the food chain. Mercury, a potent neurotoxin, has been flowing into the San Francisco Bay since the Gold Rush Era. It has settled in the bays mud and made its way up the food chain, endangering wildlife and making many fish unsafe to eat. Now a multi-billion-dollar plan aims to clean it up. Click image to the left or use the URL below. URL: | text | null |
L_0233 | mesosphere | T_1422 | Above the stratosphere is the mesosphere. Temperatures in the mesosphere decrease with altitude. Because there are few gas molecules in the mesosphere to absorb the Suns radiation, the heat source is the stratosphere below. The mesosphere is extremely cold, especially at its top, about -90o C (-130o F). | text | null |
L_0233 | mesosphere | T_1423 | The air in the mesosphere has extremely low density: 99.9% of the mass of the atmosphere is below the mesosphere. As a result, air pressure is very low (Figure 1.1). A person traveling through the mesosphere would experience severe burns from ultraviolet light since the ozone layer, which provides UV protection, is in the stratosphere below. There would be almost no oxygen for breathing. And, of course, your blood would boil at normal body temperature. Click image to the left or use the URL below. URL: | text | null |
L_0236 | metamorphic rock classification | T_1430 | Table 1.1 shows some common metamorphic rocks and their original parent rock. Picture Rock Name Slate Type of Rock Foliated Metamorphic Comments Phyllite Foliated Metamorphism of slate, but under greater heat and pressure than slate Schist Foliated Often derived from meta- morphism of claystone or shale; metamorphosed under more heat and pres- sure than phyllite Gneiss Foliated Metamorphism of various different rocks, under ex- treme conditions of heat and pressure Hornfels Non-foliated Contact metamorphism of various different rock types Metamorphism of shale Picture Rock Name Comments Quartzite Type of Metamorphic Rock Non-foliated Marble Non-foliated Metamorphism of lime- stone Metaconglomerate Non-foliated Metamorphism of con- glomerate Metamorphism of quartz sandstone Click image to the left or use the URL below. URL: | text | null |
L_0237 | metamorphic rocks | T_1431 | Any type of rock - igneous, sedimentary, or metamorphic can become a metamorphic rock. All that is needed is enough heat and/or pressure to alter the existing rocks physical or chemical makeup without melting the rock entirely. Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange and form new minerals. Ions may move between minerals to create minerals of different chemical composition. Hornfels, with its alternating bands of dark and light crystals, is a good example of how minerals rearrange themselves during metamorphism. Hornfels is shown in the table for the "Metamorphic Rock Classification" concept. | text | null |
L_0237 | metamorphic rocks | T_1432 | Extreme pressure may also lead to foliation, the flat layers that form in rocks as the rocks are squeezed by pressure (Figure 1.1). Foliation normally forms when pressure is exerted in only one direction. Metamorphic rocks may also be non-foliated. Quartzite and marble, shown in the concept "Metamorphic Rock Classification," are non-foliated. A foliated metamorphic rock. | text | null |
L_0237 | metamorphic rocks | T_1433 | The two main types of metamorphism are both related to heat within Earth: 1. Regional metamorphism: Changes in enormous quantities of rock over a wide area caused by the extreme pressure from overlying rock or from compression caused by geologic processes. Deep burial exposes the rock to high temperatures. 2. Contact metamorphism: Changes in a rock that is in contact with magma. The changes occur because of the magmas extreme heat. Click image to the left or use the URL below. URL: | text | null |
L_0238 | meteors | T_1434 | A meteor, such as in Figure 1.1, is a streak of light across the sky. People call them shooting stars but they are actually small pieces of matter burning up as they enter Earths atmosphere from space. Meteors are called meteoroids before they reach Earths atmosphere. Meteoroids are smaller than asteroids and range from the size of boulders down to the size of tiny sand grains. Still smaller objects are called interplanetary dust. When Earth passes through a cluster of meteoroids, there is a meteor shower. These clusters are often remnants left behind by comet tails. | text | null |
L_0238 | meteors | T_1435 | Although most meteors burn up in the atmosphere, larger meteoroids may strike the Earths surface to create a meteorite. Meteorites are valuable to scientists because they provide clues about our solar system. Many meteorites are from asteroids that formed when the solar system formed (Figure 1.2). A few meteorites are made of rocky material that is thought to have come from Mars when an asteroid impact shot material off the Martian surface and into space. Click image to the left or use the URL below. URL: | text | null |
L_0238 | meteors | T_1435 | Although most meteors burn up in the atmosphere, larger meteoroids may strike the Earths surface to create a meteorite. Meteorites are valuable to scientists because they provide clues about our solar system. Many meteorites are from asteroids that formed when the solar system formed (Figure 1.2). A few meteorites are made of rocky material that is thought to have come from Mars when an asteroid impact shot material off the Martian surface and into space. Click image to the left or use the URL below. URL: | text | null |
L_0240 | milky way | T_1438 | The Milky Way Galaxy, which is our galaxy. The Milky Way is made of millions of stars along with a lot of gas and dust. It looks different from other galaxies because we are looking at the main disk from within the galaxy. Astronomers estimate that the Milky Way contains 200 to 400 billion stars. | text | null |
L_0240 | milky way | T_1439 | Although it is difficult to know what the shape of the Milky Way Galaxy is because we are inside of it, astronomers have identified it as a typical spiral galaxy containing about 200 billion to 400 billion stars (Figure 1.1). An artists rendition of what astronomers think the Milky Way Galaxy would look like seen from above. The Sun is located approximately where the arrow points. Like other spiral galaxies, our galaxy has a disk, a central bulge, and spiral arms. The disk is about 100,000 light- years across and 3,000 light-years thick. Most of the Galaxys gas, dust, young stars, and open clusters are in the disk. What evidence do astronomers find that lets them know that the Milky Way is a spiral galaxy? 1. The shape of the galaxy as we see it (Figure 1.2). 2. The velocities of stars and gas in the galaxy show a rotational motion. 3. The gases, color, and dust are typical of spiral galaxies. The central bulge is about 12,000 to 16,000 light-years wide and 6,000 to 10,000 light-years thick. The central bulge contains mostly older stars and globular clusters. Some recent evidence suggests the bulge might not be spherical, but is instead shaped like a bar. The bar might be as long as 27,000 light-years long. The disk and bulge are surrounded by a faint, spherical halo, which also contains old stars and globular clusters. Astronomers have discovered that there is a gigantic black hole at the center of the galaxy. The Milky Way Galaxy is a big place. If our solar system were the size of your fist, the Galaxys disk would still be An infrared image of the Milky Way shows the long thin line of stars and the central bulge typical of spiral galaxies. wider than the entire United States! | text | null |
L_0240 | milky way | T_1439 | Although it is difficult to know what the shape of the Milky Way Galaxy is because we are inside of it, astronomers have identified it as a typical spiral galaxy containing about 200 billion to 400 billion stars (Figure 1.1). An artists rendition of what astronomers think the Milky Way Galaxy would look like seen from above. The Sun is located approximately where the arrow points. Like other spiral galaxies, our galaxy has a disk, a central bulge, and spiral arms. The disk is about 100,000 light- years across and 3,000 light-years thick. Most of the Galaxys gas, dust, young stars, and open clusters are in the disk. What evidence do astronomers find that lets them know that the Milky Way is a spiral galaxy? 1. The shape of the galaxy as we see it (Figure 1.2). 2. The velocities of stars and gas in the galaxy show a rotational motion. 3. The gases, color, and dust are typical of spiral galaxies. The central bulge is about 12,000 to 16,000 light-years wide and 6,000 to 10,000 light-years thick. The central bulge contains mostly older stars and globular clusters. Some recent evidence suggests the bulge might not be spherical, but is instead shaped like a bar. The bar might be as long as 27,000 light-years long. The disk and bulge are surrounded by a faint, spherical halo, which also contains old stars and globular clusters. Astronomers have discovered that there is a gigantic black hole at the center of the galaxy. The Milky Way Galaxy is a big place. If our solar system were the size of your fist, the Galaxys disk would still be An infrared image of the Milky Way shows the long thin line of stars and the central bulge typical of spiral galaxies. wider than the entire United States! | text | null |
L_0240 | milky way | T_1440 | Our solar system, including the Sun, Earth, and all the other planets, is within one of the spiral arms in the disk of the Milky Way Galaxy. Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm. We are about 26,000 light-years from the center of the galaxy, a little more than halfway out from the center of the galaxy to the edge. Just as Earth orbits the Sun, the Sun and solar system orbit the center of the Galaxy. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago. Astronomers have recently discovered that at the center of the Milky Way, and most other galaxies, is a supermassive black hole, although a black hole cannot be seen. This video describes the solar system in which we live. It is located in an outer edge of the Milky Way galaxy, which spans 100,000 light years. Click image to the left or use the URL below. URL: The Universe contains many billions of stars and there are many billions of galaxies. Our home, the Milky Way galaxy, is only one. Click image to the left or use the URL below. URL: | text | null |
L_0246 | moon | T_1473 | The Moon is Earths only natural satellite, a body that moves around a larger body in space. The Moon orbits Earth for the same reason Earth orbits the Sun gravity. The Moon is 3,476 km in diameter, about one-fourth the size of Earth. The satellite is also not as dense as the Earth; gravity on the Moon is only one-sixth as strong as it is on Earth. An astronaut can jump six times as high on the Moon as on Earth! The Moon makes one complete orbit around the Earth every 27.3 days. The Moon also rotates on its axis once every 27.3 days. Do you know what this means? The same side of the Moon always faces Earth, so that side of the Moon is what we always see in the night sky (Figure 1.1). The Moon makes no light of its own, but instead only reflects light from the Sun. (a) The near side of the Moon faces Earth continually. It has a thinner crust with many more maria (flat areas of basaltic rock). (b) The far side of the Moon has only been seen by spacecraft. It has a thicker crust and far fewer maria (flat areas of basaltic rock). | text | null |
L_0246 | moon | T_1474 | The Moon has no atmosphere. Since an atmosphere moderates temperature, the Moons average surface temperature during the day is approximately 225 F, but drops to -243 F at night. The coldest temperatures, around -397 F, occur in craters in the permanently shaded south polar basin. These are among the coldest temperatures recorded in the entire solar system. Earths landscape is extremely varied, with mountains, valleys, plains and hills. This landscape is always changing as plate tectonics builds new features and weathering and erosion destroys them. The landscape of the Moon is very different. With no plate tectonics, features are not built. With no atmosphere, features are not destroyed. Still, the Moon has a unique surface. Lunar surface features include the bowl-shaped craters that are caused by meteorite impacts (Figure 1.2). If Earth did not have plate tectonics or erosion, its surface would also be covered with meteorite craters. Even from Earth, the Moon has visible dark areas and light areas. The dark areas are called maria, which means seas because thats what the ancients thought they were. In fact, the maria are not water but solid, flat areas of basaltic lava. From about 3.0 to 3.5 billion years ago the Moon was continually bombarded by meteorites. Some of these meteorites were so large that they broke through the Moons newly formed surface. Then, magma flowed out and filled the craters. Scientists estimate this meteorite-caused volcanic activity on the Moon ceased about 1.2 billion years ago, but most occurred long before that. The lighter parts of the Moon are called terrae or highlands (Figure 1.3). The terrae are higher than the maria and A crater on the surface of the Moon. include several high mountain ranges. The terrae are the light silicate minerals that precipitated out of the ancient magma ocean and formed the early lunar crust. There are no lakes, rivers, or even small puddles anywhere to be found on the Moons surface, but water in the form of ice has been found in the extremely cold craters and bound up in the lunar soil. Despite the possible presence of water, the lack of an atmosphere and the extreme temperatures make it no surprise to scientists that the Moon has absolutely no evidence of life. Life from Earth has visited the Moon and there are footprints of astronauts on the lunar surface. With no wind, rain, or living thing to disturb them, these footprints will remain as long as the Moon exists. Only an impact with a meteorite could destroy them. | text | null |
L_0246 | moon | T_1475 | Like Earth, the Moon has a distinct crust, mantle, and core. What is known about the Moons interior was determined from the analysis of rock samples gathered by astronauts and from unmanned spacecraft sent to the Moon (Figure The Moons small core, 600 to 800 kilometers in diameter, is mostly iron with some sulfur and nickel. The mantle is composed of the minerals olivine and orthopyroxene. Analysis of Moon rocks indicates that there may also be high levels of iron and titanium in the lunar mantle. A close-up of the Moon, showing maria (the dark areas) and terrae (the light areas); maria covers around 16% of the Moons surface, mostly on the side of the Moon we see. LCROSS crashed into the Moon in May 2009. This QUEST video describes the mission. After watching, look up the mission to see what they found! Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0246 | moon | T_1475 | Like Earth, the Moon has a distinct crust, mantle, and core. What is known about the Moons interior was determined from the analysis of rock samples gathered by astronauts and from unmanned spacecraft sent to the Moon (Figure The Moons small core, 600 to 800 kilometers in diameter, is mostly iron with some sulfur and nickel. The mantle is composed of the minerals olivine and orthopyroxene. Analysis of Moon rocks indicates that there may also be high levels of iron and titanium in the lunar mantle. A close-up of the Moon, showing maria (the dark areas) and terrae (the light areas); maria covers around 16% of the Moons surface, mostly on the side of the Moon we see. LCROSS crashed into the Moon in May 2009. This QUEST video describes the mission. After watching, look up the mission to see what they found! Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0248 | natural gas power | T_1480 | Natural gas, often known simply as gas, is composed mostly of the hydrocarbon methane. The amount of natural gas being extracted and used in the Untied States is increasing rapidly. | text | null |
L_0248 | natural gas power | T_1481 | Natural gas forms under the same conditions that create oil. Organic material buried in the sediments harden to become a shale formation that is the source of the gas. Although natural gas forms at higher temperatures than crude oil, the two are often found together. The largest natural gas reserves in the United States are in the Appalachian Basin, North Dakota and Montana, Texas, and the Gulf of Mexico region (Figure 1.1). California also has natural gas, found mostly in the Central Valley. In the northern Sacramento Valley and the Sacramento Delta, a sediment-filled trough formed along a location where crust was pushed together (an ancient convergent margin). Gas production in the lower 48 United States. | text | null |
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