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L_0262 | paleozoic and mesozoic seas | T_1536 | Some of the most important events of the Paleozoic and Mesozoic were the rising and falling of sea level over the continents. Sea level rises over the land during a marine transgression. During a marine regression, sea level retreats. During the Paleozoic there were four complete cycles of marine transgressions and regressions. There were two additional cycles during the Mesozoic (Figure 1.1). One of two things must happen for sea level to change in a marine transgression: either the land must sink or the water level must rise. What could cause sea level to rise? When little or no fresh water is tied up in glaciers and ice caps, sea level is high. Sea level also appears to rise if land is down dropped. Sea level rises if an increase in seafloor spreading rate buoys up the ocean crust, causing the ocean basin to become smaller. What could cause sea level to fall in a marine regression? Six marine transgressions and regres- sions have occurred during the Phanero- zoic. Geologists think that the Paleozoic marine transgressions and regressions were the result of the decrease and increase in the size of glaciers covering the lands. Click image to the left or use the URL below. URL: | text | null |
L_0262 | paleozoic and mesozoic seas | T_1537 | Geologists know about marine transgressions and regressions from the sedimentary rock record. These events leave characteristic rock layers known as sedimentary facies. On a shoreline, sand and other coarse grained rock fragments are commonly found on the beach where the wave energy is high. Away from the shore in lower energy environments, fine-grained silt that later creates shale is deposited. In deeper, low-energy waters, carbonate mud that later hardens into limestone is deposited. | text | null |
L_0262 | paleozoic and mesozoic seas | T_1538 | The Paleozoic sedimentary rocks of the Grand Canyon contain evidence of marine transgressions and regressions, but even there the rock record is not complete. Look at the sequence in the Figure 1.2 and see if you can determine whether the sea was transgressing or regressing. At the bottom, the Tonto Group represents a marine transgression: sandstone (11), shale (10), and limestone (9) laid down during 30 million years of the Cambrian Period. The Ordovician and Silurian are unknown because of an unconformity. Above that is freshwater limestone (8), which is overlain by limestone (7) and then shale (6), indicating that the sea was regressing. After another unconformity, the rocks of the Supai Group (5) include limestone, siltstone, and sandstone indicative of a regressing sea. Above those rocks are shale (4), sandstone (3), a limestone and sandstone mix (2) showing that the sea regressed and transgressed and finally limestone (1) indicating that the sea had come back in. | text | null |
L_0263 | paleozoic plate tectonics | T_1539 | The Paleozoic is the furthest back era of the Phanerozoic and it lasted the longest. But the Paleozoic was relatively recent, beginning only 570 million years ago. Compared with the long expanse of the Precambrian, the Phanerozoic is recent history. Much more geological evidence is available for scientists to study so the Phanerozoic is much better known. The Paleozoic begins and ends with a supercontinent. At the beginning of the Paleozoic, the supercontinent Rodinia began to split up. At the end, Pangaea came together. | text | null |
L_0263 | paleozoic plate tectonics | T_1540 | A mountain-building event is called an orogeny. Orogenies take place over tens or hundreds of millions of years. As continents smash into microcontinents and island arcs collided, mountains rise. Geologists find evidence for the orogenies that took place while Pangaea was forming in many locations. For example, Laurentia collided with the Taconic Island Arc during the Taconic Orogeny (Figure 1.1). The remnants of this mountain range make up the Taconic Mountains in New York. The Taconic Orogeny is an example of a collision between a continent and a volcanic island arc. Laurentia experienced other orogenies as it merged with the northern continents. The southern continents came together to form Gondwana. When Laurentia and Gondwana collided to create Pangaea, the Appalachians rose. Geologists think they may once have been higher than the Himalayas are now. | text | null |
L_0263 | paleozoic plate tectonics | T_1541 | Pangaea was the last supercontinent on Earth. Evidence for the existence of Pangaea was what Alfred Wegener used to create his continental drift hypothesis, which was described in the chapter Plate Tectonics. As the continents move and the land masses change shape, the shape of the oceans changes too. During the time of Pangaea, about 250 million years ago, most of Earths water was collected in a huge ocean called Panthalassa (Figure 1.2). Click image to the left or use the URL below. URL: | text | null |
L_0264 | petroleum power | T_1542 | Oil is a liquid fossil fuel that is extremely useful because it can be transported easily and can be used in cars and other vehicles. Oil is currently the single largest source of energy in the world. | text | null |
L_0264 | petroleum power | T_1543 | Oil from the ground is called crude oil, which is a mixture of many different hydrocarbons. Crude oil is a thick dark brown or black liquid hydrocarbon. Oil also forms from buried dead organisms, but these are tiny organisms that live on the sea surface and then sink to the seafloor when they die. The dead organisms are kept away from oxygen by layers of other dead creatures and sediments. As the layers pile up, heat and pressure increase. Over millions of years, the dead organisms turn into liquid oil. | text | null |
L_0264 | petroleum power | T_1544 | In order to be collected, the oil must be located between a porous rock layer and an impermeable layer (Figure 1.1). Trapped above the porous rock layer and beneath the impermeable layer, the oil will remain between these layers until it is extracted from the rock. Oil (red) is found in the porous rock layer (yellow) and trapped by the impermeable layer (brown). The folded structure has allowed the oil to pool so a well can be drilled into the reservoir. To separate the different types of hydrocarbons in crude oil for different uses, the crude oil must be refined in refineries like the one shown in Figure 1.2. Refining is possible because each hydrocarbon in crude oil boils at a different temperature. When the oil is boiled in the refinery, separate equipment collects the different compounds. | text | null |
L_0264 | petroleum power | T_1545 | Most of the compounds that come out of the refining process are fuels, such as gasoline, diesel, and heating oil. Because these fuels are rich sources of energy and can be easily transported, oil provides about 90% of the energy used for transportation around the world. The rest of the compounds from crude oil are used for waxes, plastics, fertilizers, and other products. Gasoline is in a convenient form for use in cars and other transportation vehicles. In a car engine, the burned gasoline mostly turns into carbon dioxide and water vapor. The fuel releases most of its energy as heat, which causes the gases to expand. This creates enough force to move the pistons inside the engine and to power the car. Refineries like this one separate crude oil into many useful fuels and other chemi- cals. Click image to the left or use the URL below. URL: | text | null |
L_0264 | petroleum power | T_1546 | The United States does produce oil, but the amount produced is only about one-quarter as much as the nation uses. The United States has only about 1.5% of the worlds proven oil reserves, so most of the oil used by Americans must be imported from other nations. The main oil-producing regions in the United States are the Gulf of Mexico, Texas, Alaska, and California (Figure As in every type of mining, mining for oil has environmental consequences. Oil rigs are unsightly (Figure 1.4), and spills are too common (Figure 1.5). Click image to the left or use the URL below. URL: Offshore well locations in the Gulf of Mex- ico. Note that some wells are located in very deep water. Drill rigs at the San Ardo Oil Field in Monterey, California. | text | null |
L_0264 | petroleum power | T_1546 | The United States does produce oil, but the amount produced is only about one-quarter as much as the nation uses. The United States has only about 1.5% of the worlds proven oil reserves, so most of the oil used by Americans must be imported from other nations. The main oil-producing regions in the United States are the Gulf of Mexico, Texas, Alaska, and California (Figure As in every type of mining, mining for oil has environmental consequences. Oil rigs are unsightly (Figure 1.4), and spills are too common (Figure 1.5). Click image to the left or use the URL below. URL: Offshore well locations in the Gulf of Mex- ico. Note that some wells are located in very deep water. Drill rigs at the San Ardo Oil Field in Monterey, California. | text | null |
L_0265 | planet orbits in the solar system | T_1547 | Figure 1.1 shows the relative sizes of the orbits of the planets, asteroid belt, and Kuiper belt. In general, the farther away from the Sun, the greater the distance from one planets orbit to the next. The orbits of the planets are not circular but slightly elliptical, with the Sun located at one of the foci (see opening image). While studying the solar system, Johannes Kepler discovered the relationship between the time it takes a planet to make one complete orbit around the Sun, its "orbital period," and the distance from the Sun to the planet. If the orbital period of a planet is known, then it is possible to determine the planets distance from the Sun. This is how astronomers without modern telescopes could determine the distances to other planets within the solar system. How old are you on Earth? How old would you be if you lived on Jupiter? How many days is it until your birthday on Earth? How many days until your birthday if you lived on Saturn? Click image to the left or use the URL below. URL: The relative sizes of the orbits of planets in the solar system. The inner solar sys- tem and asteroid belt is on the upper left. The upper right shows the outer planets and the Kuiper belt. | text | null |
L_0266 | planets of the solar system | T_1548 | Since the time of Copernicus, Kepler, and Galileo, we have learned a lot more about our solar system. Astronomers have discovered two more planets (Uranus and Neptune), five dwarf planets (Ceres, Pluto, Makemake, Haumea, and Eris), more than 150 moons, and many, many asteroids and other small objects. Although the Sun is just an average star compared to other stars, it is by far the largest object in the solar system. The Sun is more than 500 times the mass of everything else in the solar system combined! Table 1.1 gives data on the sizes of the Sun and planets relative to Earth. Object Mass (Relative to Earth) Sun Mercury Venus Earth 333,000 Earths mass 0.06 Earths mass 0.82 Earths mass 1.00 Earths mass Diameter of Planet (Relative to Earth) 109.2 Earths diameter 0.39 Earths diameter 0.95 Earths diameter 1.00 Earths diameter Object Mass (Relative to Earth) Mars Jupiter Saturn Uranus Neptune 0.11 Earths mass 317.8 Earths mass 95.2 Earths mass 14.6 Earths mass 17.2 Earths mass Diameter of Planet (Relative to Earth) 0.53 Earths diameter 11.21 Earths diameter 9.41 Earths diameter 3.98 Earths diameter 3.81 Earths diameter | text | null |
L_0266 | planets of the solar system | T_1549 | Distances in the solar system are often measured in astronomical units (AU). One astronomical unit is defined as the distance from Earth to the Sun. 1 AU equals about 150 million km, or 93 million miles. Table 1.2 shows the distances to the planets (the average radius of orbits) in AU. The table also shows how long it takes each planet to spin on its axis (the length of a day) and how long it takes each planet to complete an orbit (the length of a year); in particular, notice how slowly Venus rotates relative to Earth. Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Average Distance from Sun (AU) 0.39 AU 0.72 1.00 1.52 5.20 9.54 19.22 30.06 Length of Day (In Earth Days) 56.84 days 243.02 1.00 1.03 0.41 0.43 0.72 0.67 Length of Year (In Earth Years) 0.24 years 0.62 1.00 1.88 11.86 29.46 84.01 164.8 Click image to the left or use the URL below. URL: | text | null |
L_0268 | ponds and lakes | T_1552 | Ponds are small bodies of fresh water that usually have no outlet; ponds are often are fed by underground springs. Like lakes, ponds are bordered by hills or low rises so the water is blocked from flowing directly downhill. | text | null |
L_0268 | ponds and lakes | T_1553 | Lakes are larger bodies of water. Lakes are usually fresh water, although the Great Salt Lake in Utah is just one exception. Water usually drains out of a lake through a river or a stream and all lakes lose water to evaporation. Lakes form in a variety of different ways: in depressions carved by glaciers, in calderas (Figure 1.1), and along tectonic faults, to name a few. Subglacial lakes are even found below a frozen ice cap. As a result of geologic history and the arrangement of land masses, most lakes are in the Northern Hemisphere. In fact, more than 60% of all the worlds lakes are in Canada most of these lakes were formed by the glaciers that covered most of Canada in the last Ice Age (Figure 1.2). Lakes are not permanent features of a landscape. Some come and go with the seasons, as water levels rise and fall. Over a longer time, lakes disappear when they fill with sediments, if the springs or streams that fill them diminish, (a) Crater Lake in Oregon is in a volcanic caldera. Lakes can also form in volcanic craters and impact craters. (b) The Great Lakes fill depressions eroded as glaciers scraped rock out from the landscape. (c) Lake Baikal, ice coated in winter in this image, formed as water filled up a tectonic faults. Lakes near Yellowknife were carved by glaciers during the last Ice Age. or if their outlets grow because of erosion. When the climate of an area changes, lakes can either expand or shrink (Figure 1.3). Lakes may disappear if precipitation significantly diminishes. Large lakes have tidal systems and currents, and can even affect weather patterns. The Great Lakes in the United States contain 22% of the worlds fresh surface water (Figure 1.1). The largest them, Lake Superior, has a tide that rises and falls several centimeters each day. The Great Lakes are large enough to alter the weather system in Northeastern United States by the lake effect, which is an increase in snow downwind of the relatively warm lakes. The Great Lakes are home to countless species of fish and wildlife. Many lakes are not natural, but are human-made. People dam a stream in a suitable spot and then let the water back up behind it, creating a lake. These lakes are called "reservoirs." Click image to the left or use the URL below. URL: | text | null |
L_0268 | ponds and lakes | T_1553 | Lakes are larger bodies of water. Lakes are usually fresh water, although the Great Salt Lake in Utah is just one exception. Water usually drains out of a lake through a river or a stream and all lakes lose water to evaporation. Lakes form in a variety of different ways: in depressions carved by glaciers, in calderas (Figure 1.1), and along tectonic faults, to name a few. Subglacial lakes are even found below a frozen ice cap. As a result of geologic history and the arrangement of land masses, most lakes are in the Northern Hemisphere. In fact, more than 60% of all the worlds lakes are in Canada most of these lakes were formed by the glaciers that covered most of Canada in the last Ice Age (Figure 1.2). Lakes are not permanent features of a landscape. Some come and go with the seasons, as water levels rise and fall. Over a longer time, lakes disappear when they fill with sediments, if the springs or streams that fill them diminish, (a) Crater Lake in Oregon is in a volcanic caldera. Lakes can also form in volcanic craters and impact craters. (b) The Great Lakes fill depressions eroded as glaciers scraped rock out from the landscape. (c) Lake Baikal, ice coated in winter in this image, formed as water filled up a tectonic faults. Lakes near Yellowknife were carved by glaciers during the last Ice Age. or if their outlets grow because of erosion. When the climate of an area changes, lakes can either expand or shrink (Figure 1.3). Lakes may disappear if precipitation significantly diminishes. Large lakes have tidal systems and currents, and can even affect weather patterns. The Great Lakes in the United States contain 22% of the worlds fresh surface water (Figure 1.1). The largest them, Lake Superior, has a tide that rises and falls several centimeters each day. The Great Lakes are large enough to alter the weather system in Northeastern United States by the lake effect, which is an increase in snow downwind of the relatively warm lakes. The Great Lakes are home to countless species of fish and wildlife. Many lakes are not natural, but are human-made. People dam a stream in a suitable spot and then let the water back up behind it, creating a lake. These lakes are called "reservoirs." Click image to the left or use the URL below. URL: | text | null |
L_0268 | ponds and lakes | T_1553 | Lakes are larger bodies of water. Lakes are usually fresh water, although the Great Salt Lake in Utah is just one exception. Water usually drains out of a lake through a river or a stream and all lakes lose water to evaporation. Lakes form in a variety of different ways: in depressions carved by glaciers, in calderas (Figure 1.1), and along tectonic faults, to name a few. Subglacial lakes are even found below a frozen ice cap. As a result of geologic history and the arrangement of land masses, most lakes are in the Northern Hemisphere. In fact, more than 60% of all the worlds lakes are in Canada most of these lakes were formed by the glaciers that covered most of Canada in the last Ice Age (Figure 1.2). Lakes are not permanent features of a landscape. Some come and go with the seasons, as water levels rise and fall. Over a longer time, lakes disappear when they fill with sediments, if the springs or streams that fill them diminish, (a) Crater Lake in Oregon is in a volcanic caldera. Lakes can also form in volcanic craters and impact craters. (b) The Great Lakes fill depressions eroded as glaciers scraped rock out from the landscape. (c) Lake Baikal, ice coated in winter in this image, formed as water filled up a tectonic faults. Lakes near Yellowknife were carved by glaciers during the last Ice Age. or if their outlets grow because of erosion. When the climate of an area changes, lakes can either expand or shrink (Figure 1.3). Lakes may disappear if precipitation significantly diminishes. Large lakes have tidal systems and currents, and can even affect weather patterns. The Great Lakes in the United States contain 22% of the worlds fresh surface water (Figure 1.1). The largest them, Lake Superior, has a tide that rises and falls several centimeters each day. The Great Lakes are large enough to alter the weather system in Northeastern United States by the lake effect, which is an increase in snow downwind of the relatively warm lakes. The Great Lakes are home to countless species of fish and wildlife. Many lakes are not natural, but are human-made. People dam a stream in a suitable spot and then let the water back up behind it, creating a lake. These lakes are called "reservoirs." Click image to the left or use the URL below. URL: | text | null |
L_0269 | population size | T_1554 | Biotic and abiotic factors determine the population size of a species in an ecosystem. What are some important biotic factors? Biotic factors include the amount of food that is available to that species and the number of organisms that also use that food source. What are some important abiotic factors? Space, water, and climate all help determine a species population. When does a population grow? A population grows when the number of births is greater than the number of deaths. When does a population shrink? When deaths exceed births. What causes a population to grow? For a population to grow there must be ample resources and no major problems. What causes a population to shrink? A population can shrink either because of biotic or abiotic limits. An increase in predators, the emergence of a new disease, or the loss of habitat are just three possible problems that will decrease a population. A population may also shrink if it grows too large for the resources required to support it. | text | null |
L_0269 | population size | T_1555 | When the number of births equals the number of deaths, the population is at its carrying capacity for that habitat. In a population at its carrying capacity, there are as many organisms of that species as the habitat can support. The carrying capacity depends on biotic and abiotic factors. If these factors improve, the carrying capacity increases. If the factors become less plentiful, the carrying capacity drops. If resources are being used faster than they are being replenished, then the species has exceeded its carrying capacity. If this occurs, the population will then decrease in size. | text | null |
L_0269 | population size | T_1556 | Every stable population has one or more factors that limit its growth. A limiting factor determines the carrying capacity for a species. A limiting factor can be any biotic or abiotic factor: nutrient, space, and water availability are examples (Figure 1.1). The size of a population is tied to its limiting factor. What happens if a limiting factor increases a lot? Is it still a limiting factor? If a limiting factor increases a lot, another factor will most likely become the new limiting factor. This may be a bit confusing, so lets look at an example of limiting factors. Say you want to make as many chocolate chip cookies as you can with the ingredients you have on hand. It turns out that you have plenty of flour and other ingredients, but only two eggs. You can make only one batch of cookies, because eggs are the limiting factor. But then your neighbor comes over with a dozen eggs. Now you have enough eggs for seven batches of cookies, but only two pounds of butter. You can make four batches of cookies, with butter as the limiting factor. If you get more butter, some other ingredient will be limiting. Species ordinarily produce more offspring than their habitat can support (Figure 1.2). If conditions improve, more young survive and the population grows. If conditions worsen, or if too many young are born, there is competition between individuals. As in any competition, there are some winners and some losers. Those individuals that survive to fill the available spots in the niche are those that are the most fit for their habitat. Click image to the left or use the URL below. URL: A frog in frog spawn. An animal produces many more offspring than will survive. | text | null |
L_0269 | population size | T_1556 | Every stable population has one or more factors that limit its growth. A limiting factor determines the carrying capacity for a species. A limiting factor can be any biotic or abiotic factor: nutrient, space, and water availability are examples (Figure 1.1). The size of a population is tied to its limiting factor. What happens if a limiting factor increases a lot? Is it still a limiting factor? If a limiting factor increases a lot, another factor will most likely become the new limiting factor. This may be a bit confusing, so lets look at an example of limiting factors. Say you want to make as many chocolate chip cookies as you can with the ingredients you have on hand. It turns out that you have plenty of flour and other ingredients, but only two eggs. You can make only one batch of cookies, because eggs are the limiting factor. But then your neighbor comes over with a dozen eggs. Now you have enough eggs for seven batches of cookies, but only two pounds of butter. You can make four batches of cookies, with butter as the limiting factor. If you get more butter, some other ingredient will be limiting. Species ordinarily produce more offspring than their habitat can support (Figure 1.2). If conditions improve, more young survive and the population grows. If conditions worsen, or if too many young are born, there is competition between individuals. As in any competition, there are some winners and some losers. Those individuals that survive to fill the available spots in the niche are those that are the most fit for their habitat. Click image to the left or use the URL below. URL: A frog in frog spawn. An animal produces many more offspring than will survive. | text | null |
L_0270 | precambrian continents | T_1557 | The first crust was made of basaltic rock, like the current ocean crust. Partial melting of the lower portion of the basaltic crust began more than 4 billion years ago. This created the silica-rich crust that became the felsic continents. | text | null |
L_0270 | precambrian continents | T_1558 | The earliest felsic continental crust is now found in the ancient cores of continents, called the cratons. Rapid plate motions meant that cratons experienced many continental collisions. Little is known about the paleogeography, or the ancient geography, of the early planet, although smaller continents could have come together and broken up. Geologists can learn many things about the Pre-Archean by studying the rocks of the cratons. Cratons also contain felsic igneous rocks, which are remnants of the first continents. Cratonic rocks contain rounded sedimentary grains. Of what importance is this fact? Rounded grains indicate that the minerals eroded from an earlier rock type and that rivers or seas also existed. One common rock type in the cratons is greenstone, a metamorphosed volcanic rock (Figure 1.1). Since greenstones are found today in oceanic trenches, what does the presence of greenstones mean? These ancient greenstones indicate the presence of subduction zones. Ice age glaciers scraped the Canadian Shield down to the 4.28 billion year old greenstone in Northwestern Quebec. | text | null |
L_0270 | precambrian continents | T_1559 | Places the craton crops out at the surface is known as a shield. Cratons date from the Precambrian and are called Precambrian shields. Many Precambrian shields are about 570 million years old (Figure 1.2). The Canadian Shield is the ancient flat part of Canada that lies around Hudson Bay, the northern parts of Minnesota, Wisconsin and Michigan and much of Greenland. | text | null |
L_0270 | precambrian continents | T_1560 | In most places the cratons were covered by younger rocks, which together are called a platform. Sometimes the younger rocks eroded away to expose the Precambrian craton (Figure 1.3). | text | null |
L_0270 | precambrian continents | T_1561 | During the Pre-Archean and Archean, Earths interior was warmer than today. Mantle convection was faster and plate tectonics processes were more vigorous. Since subduction zones were more common, the early crustal plates were relatively small. Since the time that it was completely molten, Earth has been cooling. Still, about half the internal heat that was generated when Earth formed remains in the planet and is the source of the heat in the core and mantle today. | text | null |
L_0271 | precambrian plate tectonics | T_1562 | By the end of the Archean, about 2.5 billion years ago, plate tectonics processes were completely recognizable. Small Proterozoic continents known as microcontinents collided to create supercontinents, which resulted in the uplift of massive mountain ranges. The history of the North American craton is an example of what generally happened to the cratons during the Precambrian. As the craton drifted, it collided with microcontinents and oceanic island arcs, which were added to the continents. Convergence was especially active between 1.5 and 1.0 billion years ago. These lands came together to create the continent of Laurentia. About 1.1 billion years ago, Laurentia became part of the supercontinent Rodinia (Figure 1.1). Rodinia probably contained all of the landmass at the time, which was about 75% of the continental landmass present today. Rodinia broke up about 750 million years ago. The geological evidence for this breakup includes large lava flows that are found where continental rifting took place. Seafloor spreading eventually started and created the oceans between the continents. The breakup of Rodinia may have triggered Snowball Earth around 700 million years ago. | text | null |
L_0277 | preventing hazardous waste problems | T_1581 | Nations that have more industry produce more hazardous waste. Currently, the United States is the worlds largest producer of hazardous wastes, but China, which produces so many products for the developed world, may soon take over the number-one spot. Countries with more industry produce more hazardous wastes than those with little industry. Problems with haz- ardous wastes and their disposal became obvious sooner in the developed world than in the developing world. As a result, many developed nations, including the United States, have laws to help control hazardous waste disposal and to clean toxic sites. As mentioned in the "Impacts of Hazardous Waste" concept, the Superfund Act requires companies to clean up contaminated sites that are designated as Superfund sites (Figure 1.1). If a responsible party cannot be identified, because the company has gone out of business or its culpability cannot be proven, the federal government pays for the cleanup out of a trust fund with money put aside by the petroleum and chemical industries. As a result of the Superfund Act, companies today are more careful about how they deal with hazardous substances. Superfund sites are located all over the nation and many are waiting to be cleaned up. The Resource Conservation and Recovery Act of 1976 requires that companies keep track of any hazardous materials they produce. These materials must be disposed of using government guidelines and records must be kept to show the government that the wastes were disposed of safely. Workers must be protected from the hazardous materials. To some extent, individuals can control the production and disposal of hazardous wastes. We can choose to use materials that are not hazardous, such as using vinegar as a cleanser. At home, people can control the amount of pesticides that they use (or they can use organic methods of pest control). It is also necessary to dispose of hazardous materials properly by not pouring them over the land, down the drain or toilet, or into a sewer or trashcan. Click image to the left or use the URL below. URL: | text | null |
L_0278 | principle of horizontality | T_1582 | Sedimentary rocks follow certain rules. 1. Sedimentary rocks are formed with the oldest layers on the bottom and the youngest on top. 2. Sediments are deposited horizontally, so sedimentary rock layers are originally horizontal, as are some vol- canic rocks, such as ash falls. 3. Sedimentary rock layers that are not horizontal are deformed. Since sedimentary rocks follow these rules, they are useful for seeing the effects of stress on rocks. Sedimentary rocks that are not horizontal must have been deformed. You can trace the deformation a rock has experienced by seeing how it differs from its original horizontal, oldest- on-bottom position. This deformation produces geologic structures such as folds, joints, and faults that are caused by stresses. | text | null |
L_0278 | principle of horizontality | T_1583 | Youre standing in the Grand Canyon and you see rocks like those in the Figure 1.1. Using the rules listed above, try to figure out the geologic history of the geologic column. The Grand Canyon is full mostly of sedimentary rocks, which are important for deciphering the geologic history of a region. In the Grand Canyon, the rock layers are exposed like a layer cake. Each layer is made of sediments that were deposited in a particular environment - perhaps a lake bed, shallow offshore region, or a sand dune. (a) The rocks of the Grand Canyon are like a layer cake. (b) A geologic column showing the rocks of the Grand Canyon. In this geologic column of the Grand Canyon, the sedimentary rocks of groups 3 through 6 are still horizontal. Group 2 rocks have been tilted. Group 1 rocks are not sedimentary. The oldest layers are on the bottom and youngest are on the top. The ways geologists figure out the geological history of an area will be explored more in the chapter Earth History. Click image to the left or use the URL below. URL: | text | null |
L_0279 | principle of uniformitarianism | T_1584 | The outcrop in the Figure 1.1 is at Checkerboard Mesa in Zion National Park, Utah. It has a very interesting pattern on it. As a geology student you may ask: how did this rock form? If you poke at the rock and analyze its chemistry you will see that its made of sand. In fact, the rock formation is called the Navajo sandstone. But knowing that the rock is sandstone doesnt tell you how it formed. It would be hard to design an experiment to show how this rock formed. But we can make observations now and apply them to this rock that formed long ago. | text | null |
L_0279 | principle of uniformitarianism | T_1585 | James Hutton came up with this idea in the late 1700s. The present is the key to the past. He called this the principle of uniformitarianism. It is that if we can understand a geological process now and we find evidence of that same Checkerboard Mesa in Zion National Park, Utah. process in the past, then we can assume that the process operated the same way in the past. Hutton speculated that it has taken millions of years to shape the planet, and it is continuing to be changed. He said that there are slow, natural processes that changed, and continue to change, the planets landscape. For example, given enough time, a stream could erode a valley, or sediment could accumulate and form a new landform. Lets go back to that outcrop. What would cause sandstone to have layers that cross each other, a feature called cross-bedding? | text | null |
L_0279 | principle of uniformitarianism | T_1586 | In the photo of the Mesquite sand dune in Death Valley National Park, California (Figure 1.2), we see that wind can cause cross-bedding in sand. Cross-bedding is due to changes in wind direction. There are also ripples caused by the wind waving over the surface of the dune. Since we can observe wind forming sand dunes with these patterns now, we have a good explanation for how the Navajo sandstone formed. The Navajo sandstone is a rock formed from ancient sand dunes in which wind direction changed from time to time. This is just one example of how geologists use observations they make today to unravel what happened in Earths past. Rocks formed from volcanoes, oceans, rivers, and many other features are deciphered by looking at the geological work those features do today. Click image to the left or use the URL below. URL: | text | null |
L_0280 | principles of relative dating | T_1587 | Early geologists had no way to determine the absolute age of a geological material. If they didnt see it form, they couldnt know if a rock was one hundred years or 100 million years old. What they could do was determine the ages of materials relative to each other. Using sensible principles they could say whether one rock was older than another and when a process occurred relative to those rocks. | text | null |
L_0280 | principles of relative dating | T_1588 | Remember Nicholas Steno, who determined that fossils represented parts of once-living organisms? Steno also noticed that fossil seashells could be found in rocks and mountains far from any ocean. He wanted to explain how that could occur. Steno proposed that if a rock contained the fossils of marine animals, the rock formed from sediments that were deposited on the seafloor. These rocks were then uplifted to become mountains. This scenario led him to develop the principles that are discussed below. They are known as Stenos laws. Stenos laws are illustrated in Figure 1.1. Original horizontality: Sediments are deposited in fairly flat, horizontal layers. If a sedimentary rock is found tilted, the layer was tilted after it was formed. Lateral continuity: Sediments are deposited in continuous sheets that span the body of water that they are deposited in. When a valley cuts through sedimentary layers, it is assumed that the rocks on either side of the valley were originally continuous. Superposition: Sedimentary rocks are deposited one on top of another. The youngest layers are found at the top of the sequence, and the oldest layers are found at the bottom. (a) Original horizontality. (b) Lateral continuity. (c) Superposition. | text | null |
L_0280 | principles of relative dating | T_1589 | Other scientists observed rock layers and formulated other principles. Geologist William Smith (1769-1839) identified the principle of faunal succession, which recognizes that: Some fossil types are never found with certain other fossil types (e.g. human ancestors are never found with dinosaurs) meaning that fossils in a rock layer represent what lived during the period the rock was deposited. Older features are replaced by more modern features in fossil organisms as species change through time; e.g. feathered dinosaurs precede birds in the fossil record. Fossil species with features that change distinctly and quickly can be used to determine the age of rock layers quite precisely. Scottish geologist, James Hutton (1726-1797) recognized the principle of cross-cutting relationships. This helps geologists to determine the older and younger of two rock units (Figure 1.2). If an igneous dike (B) cuts a series of metamorphic rocks (A), which is older and which is younger? In this image, A must have existed first for B to cut across it. | text | null |
L_0280 | principles of relative dating | T_1590 | The Grand Canyon provides an excellent illustration of the principles above. The many horizontal layers of sedi- mentary rock illustrate the principle of original horizontality (Figure 1.3). The youngest rock layers are at the top and the oldest are at the bottom, which is described by the law of superposition. Distinctive rock layers, such as the Kaibab Limestone, are matched across the broad expanse of the canyon. These rock layers were once connected, as stated by the rule of lateral continuity. The Colorado River cuts through all the layers of rock to form the canyon. Based on the principle of cross- cutting relationships, the river must be younger than all of the rock layers that it cuts through. | text | null |
L_0281 | processes of the water cycle | T_1591 | The movement of water around Earths surface is the hydrological (water) cycle (Figure 1.1). Water inhabits reservoirs within the cycle, such as ponds, oceans, or the atmosphere. The molecules move between these reservoirs by certain processes, including condensation and precipitation. There are only so many water molecules and these molecules cycle around. If climate cools and glaciers and ice caps grow, there is less water for the oceans and sea level will fall. The reverse can also happen. The following section looks at the reservoirs and the processes that move water between them. | text | null |
L_0281 | processes of the water cycle | T_1592 | The Sun, many millions of kilometers away, provides the energy that drives the water cycle. Our nearest star directly impacts the water cycle by supplying the energy needed for evaporation. | text | null |
L_0281 | processes of the water cycle | T_1593 | Most of Earths water is stored in the oceans, where it can remain for hundreds or thousands of years. | text | null |
L_0281 | processes of the water cycle | T_1594 | Water changes from a liquid to a gas by evaporation to become water vapor. The Suns energy can evaporate water from the ocean surface or from lakes, streams, or puddles on land. Only the water molecules evaporate; the salts remain in the ocean or a fresh water reservoir. The water vapor remains in the atmosphere until it undergoes condensation to become tiny droplets of liquid. The droplets gather in clouds, which are blown about the globe by wind. As the water droplets in the clouds collide and grow, they fall from the sky as precipitation. Precipitation can be rain, sleet, hail, or snow. Sometimes precipitation falls back into the ocean and sometimes it falls onto the land surface. | text | null |
L_0281 | processes of the water cycle | T_1595 | When water falls from the sky as rain it may enter streams and rivers that flow downward to oceans and lakes. Water that falls as snow may sit on a mountain for several months. Snow may become part of the ice in a glacier, where it may remain for hundreds or thousands of years. Snow and ice may go directly back into the air by sublimation, the process in which a solid changes directly into a gas without first becoming a liquid. Although you probably have not seen water vapor undergoing sublimation from a glacier, you may have seen dry ice sublimate in air. Snow and ice slowly melt over time to become liquid water, which provides a steady flow of fresh water to streams, rivers, and lakes below. A water droplet falling as rain could also become part of a stream or a lake. At the surface, the water may eventually evaporate and reenter the atmosphere. | text | null |
L_0281 | processes of the water cycle | T_1596 | A significant amount of water infiltrates into the ground. Soil moisture is an important reservoir for water (Figure The moisture content of soil in the United States varies greatly. | text | null |
L_0281 | processes of the water cycle | T_1597 | Water may seep through dirt and rock below the soil and then through pores infiltrating the ground to go into Earths groundwater system. Groundwater enters aquifers that may store fresh water for centuries. Alternatively, the water may come to the surface through springs or find its way back to the oceans. | text | null |
L_0281 | processes of the water cycle | T_1598 | Plants and animals depend on water to live. They also play a role in the water cycle. Plants take up water from the soil and release large amounts of water vapor into the air through their leaves (Figure 1.3), a process known as transpiration. | text | null |
L_0281 | processes of the water cycle | T_1599 | People also depend on water as a natural resource. Not content to get water directly from streams or ponds, humans create canals, aqueducts, dams, and wells to collect water and direct it to where they want it (Figure 1.4). Clouds form above the Amazon Rainfor- est even in the dry season because of moisture from plant transpiration. Pont du Gard in France is an ancient aqueduct and bridge that was part of of a well-developed system that supplied wa- ter around the Roman empire. Click image to the left or use the URL below. URL: | text | null |
L_0281 | processes of the water cycle | T_1599 | People also depend on water as a natural resource. Not content to get water directly from streams or ponds, humans create canals, aqueducts, dams, and wells to collect water and direct it to where they want it (Figure 1.4). Clouds form above the Amazon Rainfor- est even in the dry season because of moisture from plant transpiration. Pont du Gard in France is an ancient aqueduct and bridge that was part of of a well-developed system that supplied wa- ter around the Roman empire. Click image to the left or use the URL below. URL: | text | null |
L_0282 | protecting water from pollution | T_1600 | Water pollution can be reduced in two ways: Keep the water from becoming polluted. Clean water that is already polluted. | text | null |
L_0282 | protecting water from pollution | T_1601 | Keeping water from becoming polluted often requires laws to be sure that people and companies behave responsibly. In the United States, the Clean Water Act gives the Environmental Protection Agency (EPA) the authority to set standards for water quality for industry, agriculture, and domestic uses. The law gives the EPA the authority to reduce the discharge of pollution into waterways, finance wastewater treatment plants, and manage runoff. Since its passage in 1972, more wastewater treatment plants have been constructed and the release of industrial waste into the water supply is better controlled. Scientists control water pollution by sam- pling the water and studying the pollutants that are in the water. The United Nations and other international groups are working to improve global water quality standards by pro- viding the technology for treating water. These organizations also educate people in how to protect and improve the quality of the water they use (Figure 1.1). Click image to the left or use the URL below. URL: | text | null |
L_0282 | protecting water from pollution | T_1602 | The goal of water treatment is to make water suitable for such uses as drinking, medicine, agriculture, and industrial processes. People living in developed countries suffer from few waterborne diseases and illness, because they have extensive water treatment systems to collect, treat, and redeliver clean water. Many underdeveloped nations have few or no water treatment facilities. Wastewater contains hundreds of contaminants, such as suspended solids, oxygen-demanding materials, dissolved inorganic compounds, and harmful bacteria. In a wastewater treatment plant, multiple processes must be used to produce usable water: Sewage treatment removes contaminants, such as solids and particles, from sewage. Water purification produces drinking water by removing bacteria, algae, viruses, fungi, unpleasant elements such as iron and sulfur, and man-made chemical pollutants. The treatment method used depends on the kind of wastewater being treated and the desired end result. Wastewater is treated using a series of steps, each of which produces water with fewer contaminants. | text | null |
L_0282 | protecting water from pollution | T_1603 | What can individuals do to protect water quality? Find approved recycling or disposal facilities for motor oil and household chemicals. Use lawn, garden, and farm chemicals sparingly and wisely. Repair automobile or boat engine leaks immediately. Keep litter, pet waste, leaves, and grass clippings out of street gutters and storm drains. Click image to the left or use the URL below. URL: | text | null |
L_0283 | radioactive decay as a measure of age | T_1604 | Radioactivity is the tendency of certain atoms to decay into lighter atoms, a process that emits energy. Radioactivity also provides a way to find the absolute age of a rock. First, we need to know about radioactive decay. | text | null |
L_0283 | radioactive decay as a measure of age | T_1605 | Some isotopes are radioactive; radioactive isotopes are unstable and spontaneously change by gaining or losing particles. Two types of radioactive decay are relevant to dating Earth materials (Table 1.1): Particle Alpha Composition 2 protons, 2 neutrons Beta 1 electron Effect on Nucleus The nucleus contains two fewer protons and two fewer neutrons. One neutron decays to form a pro- ton and an electron. The electron is emitted. The radioactive decay of a parent isotope (the original element) leads to the formation of stable daughter product, also known as daughter isotope. As time passes, the number of parent isotopes decreases and the number of daughter isotopes increases (Figure 1.1). | text | null |
L_0283 | radioactive decay as a measure of age | T_1606 | Radioactive materials decay at known rates, measured as a unit called half-life. The half-life of a radioactive substance is the amount of time it takes for half of the parent atoms to decay. This is how the material decays over time (see Table 1.2). No. of half lives passed 0 1 2 3 4 5 6 7 8 Percent parent remaining 100 50 25 12.5 6.25 3.125 1.563 0.781 0.391 Percent daughter produced 0 50 75 87.5 93.75 96.875 98.437 99.219 99.609 Pretend you find a rock with 3.125% parent atoms and 96.875% daughter atoms. How many half lives have passed? If the half-life of the parent isotope is 1 year, then how old is the rock? The decay of radioactive materials can be shown with a graph (Figure 1.2). Notice how it doesnt take too many half lives before there is very little parent remaining and most of the isotopes are daughter isotopes. This limits how many half lives can pass before a radioactive element is no longer useful for Decay of an imaginary radioactive sub- stance with a half-life of one year. dating materials. Fortunately, different isotopes have very different half lives. Click image to the left or use the URL below. URL: | text | null |
L_0284 | radiometric dating | T_1607 | Radiometric dating is the process of using the concentrations of radioactive substances and daughter products to estimate the age of a material. Different isotopes are used to date materials of different ages. Using more than one isotope helps scientists to check the accuracy of the ages that they calculate. | text | null |
L_0284 | radiometric dating | T_1608 | Radiocarbon dating is used to find the age of once-living materials between 100 and 50,000 years old. This range is especially useful for determining ages of human fossils and habitation sites (Figure 1.1). The atmosphere contains three isotopes of carbon: carbon-12, carbon-13 and carbon-14. Only carbon-14 is radioac- tive; it has a half-life of 5,730 years. The amount of carbon-14 in the atmosphere is tiny and has been relatively stable through time. Plants remove all three isotopes of carbon from the atmosphere during photosynthesis. Animals consume this carbon when they eat plants or other animals that have eaten plants. After the organisms death, the carbon-14 decays to stable nitrogen-14 by releasing a beta particle. The nitrogen atoms are lost to the atmosphere, but the amount of carbon-14 that has decayed can be estimated by measuring the proportion of radioactive carbon-14 to stable carbon- 12. As time passes, the amount of carbon-14 decreases relative to the amount of carbon-12. Carbon isotopes from the black material in these cave paintings places their cre- ating at about 26,000 to 27,000 years BP (before present). | text | null |
L_0284 | radiometric dating | T_1609 | Potassium-40 decays to argon-40 with a half-life of 1.26 billion years. Argon is a gas so it can escape from molten magma, meaning that any argon that is found in an igneous crystal probably formed as a result of the decay of potassium-40. Measuring the ratio of potassium-40 to argon-40 yields a good estimate of the age of that crystal. Potassium is common in many minerals, such as feldspar, mica, and amphibole. With its half-life, the technique is used to date rocks from 100,000 years to over a billion years old. The technique has been useful for dating fairly young geological materials and deposits containing the bones of human ancestors. | text | null |
L_0284 | radiometric dating | T_1610 | Two uranium isotopes are used for radiometric dating. Uranium-238 decays to lead-206 with a half-life of 4.47 billion years. Uranium-235 decays to form lead-207 with a half-life of 704 million years. Uranium-lead dating is usually performed on zircon crystals (Figure 1.2). When zircon forms in an igneous rock, the crystals readily accept atoms of uranium but reject atoms of lead. If any lead is found in a zircon crystal, it can be assumed that it was produced from the decay of uranium. Uranium-lead dating is useful for dating igneous rocks from 1 million years to around 4.6 billion years old. Zircon crystals from Australia are 4.4 billion years old, among the oldest rocks on the planet. | text | null |
L_0284 | radiometric dating | T_1611 | Radiometric dating is a very useful tool for dating geological materials but it does have limits: 1. The material being dated must have measurable amounts of the parent and/or the daughter isotopes. Ideally, different radiometric techniques are used to date the same sample; if the calculated ages agree, they are thought to be accurate. 2. Radiometric dating is not very useful for determining the age of sedimentary rocks. To estimate the age of a sedimentary rock, geologists find nearby igneous rocks that can be dated and use relative dating to constrain the age of the sedimentary rock. | text | null |
L_0284 | radiometric dating | T_1612 | As youve learned, radiometric dating can only be done on certain materials. But these important numbers can still be used to get the ages of other materials! How would you do this? One way is to constrain a material that cannot be dated by one or more that can. For example, if sedimentary rock A is below volcanic rock B and the age of volcanic rock B is 2.0 million years, then you know that sedimentary rock A is older than 2.0 million years. If sedimentary rock A is above volcanic rock C and its age is 2.5 million years then you know that sedimentary rock A is between 2.0 and 2.5 million years. In this way, geologists can figure out the approximate ages of many different rock formations. | text | null |
L_0285 | reducing air pollution | T_1613 | The Clean Air Act of 1970 and the amendments since then have done a great job in requiring people to clean up the air over the United States. Emissions of the six major pollutants regulated by the Clean Air Act carbon monoxide, lead, nitrous oxides, ozone, sulfur dioxide, and particulates have decreased by more than 50%. Cars, power plants, and factories individually release less pollution than they did in the mid-20th century. But there are many more cars, power plants, and factories. Many pollutants are still being released and some substances have been found to be pollutants that were not known to be pollutants in the past. There is still much work to be done to continue to clean up the air. | text | null |
L_0285 | reducing air pollution | T_1614 | Reducing air pollution from vehicles can be done in a number of ways. Breaking down pollutants before they are released into the atmosphere. Motor vehicles emit less pollution than they once did because of catalytic converters (Figure 1.1). Catalytic converters contain a catalyst that speeds up chemical reactions and breaks down nitrous oxides, carbon monoxide, and VOCs. Catalytic converters only work when they are hot, so a lot of exhaust escapes as the car is warming up. Catalytic converters are placed on mod- ern cars in the United States. Making a vehicle more fuel efficient. Lighter, more streamlined vehicles need less energy. Hybrid vehicles have an electric motor and a rechargeable battery. The energy that would be lost during braking is funneled into charging the battery, which then can power the car. The internal combustion engine only takes over when power in the battery has run out. Hybrids can reduce auto emissions by 90% or more, but many models do not maximize the possible fuel efficiency of the vehicle. A plug-in hybrid is plugged into an electricity source when it is not in use, perhaps in a garage, to make sure that the battery is charged. Plug-in hybrids run for a longer time on electricity and so are less polluting than regular hybrids. Plug-in hybrids began to become available in 2010. Developing new technologies that do not use fossil fuels. Fueling a car with something other than a liquid organic-based fuel is difficult. A fuel cell converts chemical energy into electrical energy. Hydrogen fuel cells harness the energy released when hydrogen and oxygen come together to create water (Figure 1.2). Fuel cells are extremely efficient and they produce no pollutants. But developing fuel-cell technology has had many problems and no one knows when or if they will become practical. | text | null |
L_0285 | reducing air pollution | T_1615 | Pollutants are removed from the exhaust streams of power plants and industrial plants before they enter the atmo- sphere. Particulates can be filtered out, and sulfur and nitric oxides can be broken down by catalysts. Removing these oxides reduces the pollutants that cause acid rain. Particles are relatively easy to remove from emissions by using motion or electricity to separate particles from the gases. Scrubbers remove particles and waste gases from exhaust using liquids or neutralizing materials (Figure 1.3). Gases, such as nitrogen oxides, can be broken down at very high temperatures. A hydrogen fuel-cell car looks like a gasoline-powered car. Scrubbers remove particles and waste gases from exhaust. | text | null |
L_0285 | reducing air pollution | T_1615 | Pollutants are removed from the exhaust streams of power plants and industrial plants before they enter the atmo- sphere. Particulates can be filtered out, and sulfur and nitric oxides can be broken down by catalysts. Removing these oxides reduces the pollutants that cause acid rain. Particles are relatively easy to remove from emissions by using motion or electricity to separate particles from the gases. Scrubbers remove particles and waste gases from exhaust using liquids or neutralizing materials (Figure 1.3). Gases, such as nitrogen oxides, can be broken down at very high temperatures. A hydrogen fuel-cell car looks like a gasoline-powered car. Scrubbers remove particles and waste gases from exhaust. | text | null |
L_0285 | reducing air pollution | T_1616 | Gasification is a developing technology. In gasification, coal (rarely is another organic material used) is heated to extremely high temperatures to create syngas, which is then filtered. The energy goes on to drive a generator. Syngas releases about 80% less pollution than regular coal plants, and greenhouse gases are also lower. Clean coal plants do not need scrubbers or other pollution control devices. Although the technology is ready, clean coal plants are more expensive to construct and operate. Also, heating the coal to high enough temperatures uses a great deal of energy, so the technology is not energy efficient. In addition, large amounts of the greenhouse gas CO2 are still released with clean coal technology. Nonetheless, a few of these plants are operating in the United States and around the world. | text | null |
L_0285 | reducing air pollution | T_1617 | How can air pollution be reduced? Using less fossil fuel is one way to lessen pollution. Some examples of ways to conserve fossil fuels are: Riding a bike or walking instead of driving. Taking a bus or carpooling. Buying a car that has greater fuel efficiency. Turning off lights and appliances when they are not in use. Using energy efficient light bulbs and appliances. Buying fewer things that are manufactured using fossil fuels. All these actions reduce the amount of energy that power plants need to produce. Click image to the left or use the URL below. URL: Developing alternative energy sources is important. What are some of the problems facing wider adoption of alternative energy sources? The technologies for several sources of alternative energy, including solar and wind, are still being developed. Solar and wind are still expensive relative to using fossil fuels. The technology needs to advance so that the price falls. Some areas get low amounts of sunlight and are not suited for solar. Others do not have much wind. It is important that regions develop what best suits them. While the desert Southwest will need to develop solar, the Great Plains can use wind energy as its energy source. Perhaps some locations will rely on nuclear power plants, although current nuclear power plants have major problems with safety and waste disposal. Sometimes technological approaches are what is needed. Click image to the left or use the URL below. URL: | text | null |
L_0286 | reducing ozone destruction | T_1618 | One success story in reducing pollutants that harm the atmosphere concerns ozone-destroying chemicals. In 1973, scientists calculated that CFCs could reach the stratosphere and break apart. This would release chlorine atoms, which would then destroy ozone. Based only on their calculations, the United States and most Scandinavian countries banned CFCs in spray cans in 1978. More confirmation that CFCs break down ozone was needed before more was done to reduce production of ozone- destroying chemicals. In 1985, members of the British Antarctic Survey reported that a 50% reduction in the ozone layer had been found over Antarctica in the previous three springs. | text | null |
L_0286 | reducing ozone destruction | T_1619 | Two years after the British Antarctic Survey report, the "Montreal Protocol on Substances that Deplete the Ozone Layer" was ratified by nations all over the world. The Montreal Protocol controls the production and consumption of 96 chemicals that damage the ozone layer (Figure 1.1). Hazardous substances are phased out first by developed nations and one decade later by developing nations. More hazardous substances are phased out more quickly. CFCs have been mostly phased out since 1995, although were used in developing nations until 2010. Some of the less hazardous substances will not be phased out until 2030. The Protocol also requires that wealthier nations donate money to develop technologies that will replace these chemicals. Ozone levels over North America decreased between 1974 and 2009. Models of the future predict what ozone levels would have been if CFCs were not being phased out. Warmer colors indicate more ozone. Since CFCs take many years to reach the stratosphere and can survive there a long time before they break down, the ozone hole will probably continue to grow for some time before it begins to shrink. The ozone layer will reach the same levels it had before 1980 around 2068 and 1950 levels in one or two centuries. | text | null |
L_0287 | revolutions of earth | T_1620 | Certainly no one today doubts that Earth orbits a star, the Sun. Photos taken from space, observations made by astronauts, and the fact that there has been so much successful space exploration that depends on understanding the structure of the solar system all confirm it. But in the early 17th century saying that Earth orbited the Sun rather than the reverse could get you tried for heresy, as it did Galileo. Lets explore the evolution of the idea that Earth orbits the Sun. | text | null |
L_0287 | revolutions of earth | T_1621 | To an observer, Earth appears to be the center of the universe. That is what the ancient Greeks believed. This view is called the geocentric model, or "Earth-centered" model, of the universe. In the geocentric model, the sky, or heavens, are a set of spheres layered on top of one another. Each object in the sky is attached to a sphere and moves around Earth as that sphere rotates. From Earth outward, these spheres contain the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn. An outer sphere holds all the stars. Since the planets appear to move much faster than the stars, the Greeks placed them closer to Earth. The geocentric model explained why all the stars appear to rotate around Earth once per day. The model also explained why the planets move differently from the stars and from each other. One problem with the geocentric model is that some planets seem to move backwards (in retrograde) instead of in their usual forward motion around Earth. Around 150 A.D. the astronomer Ptolemy resolved this problem by using a system of circles to describe the motion of planets (Figure 1.1). In Ptolemys system, a planet moves in a small circle, called an epicycle. This circle moves around Earth in a larger circle, called a deferent. Ptolemys version of the geocentric model worked so well that it remained the accepted model of the universe for more than a thousand years. | text | null |
L_0287 | revolutions of earth | T_1622 | Ptolemys geocentric model worked, but it was complicated and occasionally made errors in predicting the movement of planets. At the beginning of the 16th century A.D., Nicolaus Copernicus proposed that Earth and all the other planets orbit the Sun. With the Sun at the center, this model is called the heliocentric model, or "sun-centered" model. Although Copernicus model was simpler - it didnt need epicycles and deferents - it still did not perfectly describe the motion of the planets. Johannes Kepler solved the problem a short time later when he determined that the planets moved around the Sun in ellipses (ovals), not circles (Figure 1.2). Keplers model matched observations perfectly. The heliocentric model did not catch on right away. When Galileo Galilei first turned a telescope to the heavens in 1610, he made several striking discoveries. Galileo discovered that the planet Jupiter has moons orbiting around it. This provided the first evidence that objects could orbit something besides Earth. Galileo also discovered that Venus has phases like the Moon (Figure 1.3), which provides direct evidence that Venus orbits the Sun. Galileos discoveries caused many more people to accept the heliocentric model of the universe, although Galileo himself was found guilty of heresy. The shift from an Earth-centered view to a Sun-centered view of the universe is referred to as the Copernican Revolution. In their elliptical orbits, each planet is sometimes farther away from the Sun than at other times. This movement is called revolution. At the same time, Earth spins on its axis. Earths axis is an imaginary line passing through the Keplers model showed the planets moving around the Sun in ellipses. The phases of Venus. planets center that goes through both the North Pole and the South Pole. This spinning movement is called Earths rotation. | text | null |
L_0287 | revolutions of earth | T_1622 | Ptolemys geocentric model worked, but it was complicated and occasionally made errors in predicting the movement of planets. At the beginning of the 16th century A.D., Nicolaus Copernicus proposed that Earth and all the other planets orbit the Sun. With the Sun at the center, this model is called the heliocentric model, or "sun-centered" model. Although Copernicus model was simpler - it didnt need epicycles and deferents - it still did not perfectly describe the motion of the planets. Johannes Kepler solved the problem a short time later when he determined that the planets moved around the Sun in ellipses (ovals), not circles (Figure 1.2). Keplers model matched observations perfectly. The heliocentric model did not catch on right away. When Galileo Galilei first turned a telescope to the heavens in 1610, he made several striking discoveries. Galileo discovered that the planet Jupiter has moons orbiting around it. This provided the first evidence that objects could orbit something besides Earth. Galileo also discovered that Venus has phases like the Moon (Figure 1.3), which provides direct evidence that Venus orbits the Sun. Galileos discoveries caused many more people to accept the heliocentric model of the universe, although Galileo himself was found guilty of heresy. The shift from an Earth-centered view to a Sun-centered view of the universe is referred to as the Copernican Revolution. In their elliptical orbits, each planet is sometimes farther away from the Sun than at other times. This movement is called revolution. At the same time, Earth spins on its axis. Earths axis is an imaginary line passing through the Keplers model showed the planets moving around the Sun in ellipses. The phases of Venus. planets center that goes through both the North Pole and the South Pole. This spinning movement is called Earths rotation. | text | null |
L_0287 | revolutions of earth | T_1623 | Copernicus, Galileo, and Kepler were all right: Earth and the other planets travel in an elliptical orbit around the Sun. The gravitational pull of the Sun keeps the planets in orbit. This ellipse is barely elliptical; its very close to being a circle. The closest Earth gets to the Sun each year is at perihelion (147 million km) on about January 3rd, and the furthest is at aphelion (152 million km) on July 4th. The shape of Earths orbit has nothing to do with Earths seasons. Earth and the other planets in the solar system make elliptical orbits around the Sun. For Earth to make one complete revolution around the Sun takes 365.24 days. This amount of time is the definition of one year. Earth has one large moon, which orbits Earth once every 29.5 days, a period known as a month. Click image to the left or use the URL below. URL: | text | null |
L_0288 | rocks | T_1624 | A rock is a naturally formed, non-living Earth material. Rocks are made of collections of mineral grains that are held together in a firm, solid mass (Figure 1.1). How is a rock different from a mineral? Rocks are made of minerals. The mineral grains in a rock may be so tiny that you can only see them with a microscope, or they may be as big as your fingernail or even your finger (Figure Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive set of minerals. A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly, rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of mineral grains. Are the two samples in Figure 1.3 the same rock type? Do they have the same minerals? The same texture? The different colors and textures seen in this rock are caused by the presence of different minerals. A pegmatite from South Dakota with crystals of lepidolite, tourmaline, and quartz (1 cm scale on the upper left). Sample 2 Crystals are tiny or microscopic Magma erupted and cooled quickly Andesite As seen in Table 1.1, these two rocks have the same chemical composition and contain mostly the same minerals, but they do not have the same texture. Sample 1 has visible mineral grains, but Sample 2 has very tiny or invisible grains. The two different textures indicate different histories. Sample 1 is a diorite, a rock that cooled slowly from magma (molten rock) underground. Sample 2 is an andesite, a rock that cooled rapidly from a very similar magma that erupted onto Earths surface. A few rocks are not made of minerals because the material they are made of does not fit the definition of a mineral. Coal, for example, is made of organic material, which is not a mineral. Can you think of other rocks that are not made of minerals? 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_0288 | rocks | T_1624 | A rock is a naturally formed, non-living Earth material. Rocks are made of collections of mineral grains that are held together in a firm, solid mass (Figure 1.1). How is a rock different from a mineral? Rocks are made of minerals. The mineral grains in a rock may be so tiny that you can only see them with a microscope, or they may be as big as your fingernail or even your finger (Figure Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive set of minerals. A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly, rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of mineral grains. Are the two samples in Figure 1.3 the same rock type? Do they have the same minerals? The same texture? The different colors and textures seen in this rock are caused by the presence of different minerals. A pegmatite from South Dakota with crystals of lepidolite, tourmaline, and quartz (1 cm scale on the upper left). Sample 2 Crystals are tiny or microscopic Magma erupted and cooled quickly Andesite As seen in Table 1.1, these two rocks have the same chemical composition and contain mostly the same minerals, but they do not have the same texture. Sample 1 has visible mineral grains, but Sample 2 has very tiny or invisible grains. The two different textures indicate different histories. Sample 1 is a diorite, a rock that cooled slowly from magma (molten rock) underground. Sample 2 is an andesite, a rock that cooled rapidly from a very similar magma that erupted onto Earths surface. A few rocks are not made of minerals because the material they are made of does not fit the definition of a mineral. Coal, for example, is made of organic material, which is not a mineral. Can you think of other rocks that are not made of minerals? 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_0288 | rocks | T_1624 | A rock is a naturally formed, non-living Earth material. Rocks are made of collections of mineral grains that are held together in a firm, solid mass (Figure 1.1). How is a rock different from a mineral? Rocks are made of minerals. The mineral grains in a rock may be so tiny that you can only see them with a microscope, or they may be as big as your fingernail or even your finger (Figure Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive set of minerals. A rock may be made of grains of all one mineral type, such as quartzite. Much more commonly, rocks are made of a mixture of different minerals. Texture is a description of the size, shape, and arrangement of mineral grains. Are the two samples in Figure 1.3 the same rock type? Do they have the same minerals? The same texture? The different colors and textures seen in this rock are caused by the presence of different minerals. A pegmatite from South Dakota with crystals of lepidolite, tourmaline, and quartz (1 cm scale on the upper left). Sample 2 Crystals are tiny or microscopic Magma erupted and cooled quickly Andesite As seen in Table 1.1, these two rocks have the same chemical composition and contain mostly the same minerals, but they do not have the same texture. Sample 1 has visible mineral grains, but Sample 2 has very tiny or invisible grains. The two different textures indicate different histories. Sample 1 is a diorite, a rock that cooled slowly from magma (molten rock) underground. Sample 2 is an andesite, a rock that cooled rapidly from a very similar magma that erupted onto Earths surface. A few rocks are not made of minerals because the material they are made of does not fit the definition of a mineral. Coal, for example, is made of organic material, which is not a mineral. Can you think of other rocks that are not made of minerals? 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_0289 | rocks and processes of the rock cycle | T_1625 | The rock cycle, illustrated in Figure 1.1, depicts how the three major rock types - igneous, sedimentary, and meta- morphic - convert from one to another. Arrows connecting the rock types represent the processes that accomplish these changes. Rocks change as a result of natural processes that are taking place all the time. Most changes happen very slowly. Rocks deep within the Earth are right now becoming other types of rocks. Rocks at the surface are lying in place before they are next exposed to a process that will change them. Even at the surface, we may not notice the changes. The rock cycle has no beginning or end. | text | null |
L_0289 | rocks and processes of the rock cycle | T_1626 | Rocks are classified into three major groups according to how they form. These three types are described in more detail in other concepts in this chapter, but here is a summary. The Rock Cycle. Igneous rocks form from the cooling and hardening of molten magma in many different environments. The chemical composition of the magma and the rate at which it cools determine what rock forms. Igneous rocks can cool slowly beneath the surface or rapidly at the surface. These rocks are identified by their composition and texture. More than 700 different types of igneous rocks are known. Sedimentary rocks form by the compaction and cementing together of sediments, broken pieces of rock-like gravel, sand, silt, or clay. Those sediments can be formed from the weathering and erosion of preexisting rocks. Sedimentary rocks also include chemical precipitates, the solid materials left behind after a liquid evaporates. Metamorphic rocks form when the minerals in an existing rock are changed by heat or pressure below the surface. Click image to the left or use the URL below. URL: | text | null |
L_0289 | rocks and processes of the rock cycle | T_1627 | Several processes can turn one type of rock into another type of rock. The key processes of the rock cycle are crystallization, erosion and sedimentation, and metamorphism. | text | null |
L_0289 | rocks and processes of the rock cycle | T_1628 | Magma cools either underground or on the surface and hardens into an igneous rock. As the magma cools, different crystals form at different temperatures, undergoing crystallization. For example, the mineral olivine crystallizes out of magma at much higher temperatures than quartz. The rate of cooling determines how much time the crystals will have to form. Slow cooling produces larger crystals. | text | null |
L_0289 | rocks and processes of the rock cycle | T_1629 | Weathering wears rocks at the Earths surface down into smaller pieces. The small fragments are called sediments. Running water, ice, and gravity all transport these sediments from one place to another by erosion. During sedimen- tation, the sediments are laid down or deposited. In order to form a sedimentary rock, the accumulated sediment must become compacted and cemented together. | text | null |
L_0289 | rocks and processes of the rock cycle | T_1630 | When a rock is exposed to extreme heat and pressure within the Earth but does not melt, the rock becomes meta- morphosed. Metamorphism may change the mineral composition and the texture of the rock. For that reason, a metamorphic rock may have a new mineral composition and/or texture. | text | null |
L_0291 | rotation of earth | T_1635 | In 1851, a French scientist named Lon Foucault took an iron sphere and hung it from a wire. He pulled the sphere to one side and then released it, as a pendulum. Although a pendulum set in motion should not change its motion, Foucault observed that his pendulum did seem to change direction relative to the circle below. Foucault concluded that Earth was moving underneath the pendulum. People at that time already knew that Earth rotated on its axis, but Foucaults experiment was nice confirmation. | text | null |
L_0291 | rotation of earth | T_1636 | Imagine a line passing through the center of Earth that goes through both the North Pole and the South Pole. This imaginary line is called an axis. Earth spins around its axis, just as a top spins around its spindle. This spinning movement is called Earths rotation. An observer in space will see that Earth requires 23 hours, 59 minutes, and 4 seconds to make one complete rotation on its axis. But because Earth moves around the Sun at the same time that it is rotating, the planet must turn just a little bit more to reach the same place relative to the Sun. Hence the length of a day on Earth is actually 24 hours. At the Equator, the Earth rotates at a speed of about 1,700 km per hour, but at the poles the movement speed is nearly nothing. | text | null |
L_0291 | rotation of earth | T_1637 | Earth rotates once on its axis about every 24 hours. To an observer looking down at the North Pole, the rotation appears counterclockwise. From nearly all points on Earth, the Sun appears to move across the sky from east to west each day. Of course, the Sun is not moving from east to west at all; Earth is rotating. The Moon and stars also seem to rise in the east and set in the west. Earths rotation means that there is a cycle of daylight and darkness approximately every 24 hours, the length of a day. Different places experience sunset and sunrise at different times and the amount of daylight and darkness also differs by location. Shadows are areas where an object obstructs a light source so that darkness takes on the form of the object. On Earth, a shadow can be cast by the Sun, Moon, or (rarely) Mercury or Venus. Click image to the left or use the URL below. URL: | text | null |
L_0292 | safety of water | T_1638 | The water that comes out of our faucets is safe because it has gone through a series of treatment and purification processes to remove contaminants. Those of us who are fortunate enough to always be able to get clean water from a tap in our home may have trouble imagining life in a country that cannot afford the technology to treat and purify water. | text | null |
L_0292 | safety of water | T_1639 | Many people in the world have no choice but to drink from the same polluted river where sewage is dumped. One- fifth of all people in the world, more than 1.1 billion people, do not have access to safe water for drinking, personal cleanliness, and domestic use. Unsafe drinking water carries many pathogens, or disease-causing biological agents such as infectious bacteria and parasites. Toxic chemicals and radiological hazards in water can also cause diseases. | text | null |
L_0292 | safety of water | T_1640 | Waterborne disease caused by unsafe drinking water is the leading cause of death for children under the age of five in many nations and a cause of death and illness for many adults. About 88% of all diseases are caused by drinking unsafe water (Figure 1.1). Throughout the world, more than 14,000 people die every day from waterborne diseases, such as cholera, and many of the worlds hospital beds are occupied by patients suffering from a waterborne disease. Guinea worm is a serious problem in parts of Africa that is being eradicated. Learn what is being done to decrease the number of people suffering from this parasite at the video below. Click image to the left or use the URL below. URL: | text | null |
L_0293 | satellites shuttles and space stations | T_1641 | A rocket is propelled into space by particles flying out of one end at high speed (see Figure 1.1). A rocket in space moves like a skater holding the fire extinguisher. Fuel is ignited in a chamber, which causes an explosion of gases. The explosion creates pressure that forces the gases out of the rocket. As these gases rush out the end, the rocket moves in the opposite direction, as predicted by Newtons Third Law of Motion. The reaction force of the gases on the rocket pushes the rocket forward. The force pushing the rocket is called thrust. Nothing would get into space without being thrust upward by a rocket. | text | null |
L_0293 | satellites shuttles and space stations | T_1642 | One of the first uses of rockets in space was to launch satellites. A satellite is an object that orbits a larger object. An orbit is a circular or elliptical path around an object. The Moon was Earths first satellite, but now many human- made "artificial satellites" orbit the planet. Thousands of artificial satellites have been put into orbit around Earth (Figure 1.2). We have even put satellites into orbit around the Moon, the Sun, Venus, Mars, Jupiter, and Saturn. There are four main types of satellites. Imaging satellites take pictures of Earths surface for military or scientific purposes. Imaging satellites study the Moon and other planets. Communications satellites receive and send signals for telephone, television, or other types of communica- tions. Navigational satellites are used for navigation systems, such as the Global Positioning System (GPS). The International Space Station, the largest artificial satellite, is designed for humans to live in space while conducting scientific research. | text | null |
L_0293 | satellites shuttles and space stations | T_1643 | Humans have a presence in space at the International Space Station (ISS) (pictured in Figure 1.3). Modern space stations are constructed piece by piece to create a modular system. The primary purpose of the ISS is scientific research, especially in medicine, biology, and physics. | text | null |
L_0293 | satellites shuttles and space stations | T_1644 | Craft designed for human spaceflight, like the Apollo missions, were very successful, but were also very expensive, could not carry much cargo, and could be used only once. To outfit the ISS, NASA needed a space vehicle that was reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in (Figure 1.4). Satellites operate with solar panels for energy. A photograph of the International Space Station was taken from the space shuttle Atlantis in June 2007. Construction of the station was completed in 2011, but new pieces and experiments continue to be added. A space shuttle has three main parts. The part you are probably most familiar with is the orbiter, with wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large "booster rockets." All of this is needed to get the orbiter out of Earths atmosphere. Once in space, the orbiter can be used to release equipment (such as a satellite or supplies for the International Space Station), to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter. When the mission is complete, the orbiter re-enters Earths atmosphere and flies back to Earth more like a glider than an airplane. The Space Shuttle program did 135 missions between 1981 and 2011, when the remaining shuttles were retired. The ISS is now serviced by Russian Soyuz spacecraft. Atlantis on the launch pad in 2006. Since 1981, the space shuttle has been the United States primary vehicle for carrying people and large equipment into space. | text | null |
L_0293 | satellites shuttles and space stations | T_1644 | Craft designed for human spaceflight, like the Apollo missions, were very successful, but were also very expensive, could not carry much cargo, and could be used only once. To outfit the ISS, NASA needed a space vehicle that was reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in (Figure 1.4). Satellites operate with solar panels for energy. A photograph of the International Space Station was taken from the space shuttle Atlantis in June 2007. Construction of the station was completed in 2011, but new pieces and experiments continue to be added. A space shuttle has three main parts. The part you are probably most familiar with is the orbiter, with wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large "booster rockets." All of this is needed to get the orbiter out of Earths atmosphere. Once in space, the orbiter can be used to release equipment (such as a satellite or supplies for the International Space Station), to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter. When the mission is complete, the orbiter re-enters Earths atmosphere and flies back to Earth more like a glider than an airplane. The Space Shuttle program did 135 missions between 1981 and 2011, when the remaining shuttles were retired. The ISS is now serviced by Russian Soyuz spacecraft. Atlantis on the launch pad in 2006. Since 1981, the space shuttle has been the United States primary vehicle for carrying people and large equipment into space. | text | null |
L_0293 | satellites shuttles and space stations | T_1644 | Craft designed for human spaceflight, like the Apollo missions, were very successful, but were also very expensive, could not carry much cargo, and could be used only once. To outfit the ISS, NASA needed a space vehicle that was reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in (Figure 1.4). Satellites operate with solar panels for energy. A photograph of the International Space Station was taken from the space shuttle Atlantis in June 2007. Construction of the station was completed in 2011, but new pieces and experiments continue to be added. A space shuttle has three main parts. The part you are probably most familiar with is the orbiter, with wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large "booster rockets." All of this is needed to get the orbiter out of Earths atmosphere. Once in space, the orbiter can be used to release equipment (such as a satellite or supplies for the International Space Station), to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter. When the mission is complete, the orbiter re-enters Earths atmosphere and flies back to Earth more like a glider than an airplane. The Space Shuttle program did 135 missions between 1981 and 2011, when the remaining shuttles were retired. The ISS is now serviced by Russian Soyuz spacecraft. Atlantis on the launch pad in 2006. Since 1981, the space shuttle has been the United States primary vehicle for carrying people and large equipment into space. | text | null |
L_0293 | satellites shuttles and space stations | T_1644 | Craft designed for human spaceflight, like the Apollo missions, were very successful, but were also very expensive, could not carry much cargo, and could be used only once. To outfit the ISS, NASA needed a space vehicle that was reusable and able to carry large pieces of equipment, such as satellites, space telescopes, or sections of a space station. The resulting spacecraft was a space shuttle, shown in (Figure 1.4). Satellites operate with solar panels for energy. A photograph of the International Space Station was taken from the space shuttle Atlantis in June 2007. Construction of the station was completed in 2011, but new pieces and experiments continue to be added. A space shuttle has three main parts. The part you are probably most familiar with is the orbiter, with wings like an airplane. When a space shuttle launches, the orbiter is attached to a huge fuel tank that contains liquid fuel. On the sides of the fuel tank are two large "booster rockets." All of this is needed to get the orbiter out of Earths atmosphere. Once in space, the orbiter can be used to release equipment (such as a satellite or supplies for the International Space Station), to repair existing equipment such as the Hubble Space Telescope, or to do experiments directly on board the orbiter. When the mission is complete, the orbiter re-enters Earths atmosphere and flies back to Earth more like a glider than an airplane. The Space Shuttle program did 135 missions between 1981 and 2011, when the remaining shuttles were retired. The ISS is now serviced by Russian Soyuz spacecraft. Atlantis on the launch pad in 2006. Since 1981, the space shuttle has been the United States primary vehicle for carrying people and large equipment into space. | text | null |
L_0294 | saturn | T_1645 | Saturn, shown in Figure 1.1, is famous for its beautiful rings. Although all the gas giants have rings, only Saturns can be easily seen from Earth. In Roman mythology, Saturn was the father of Jupiter. Saturns mass is about 95 times the mass of Earth, and its volume is 755 times Earths volume, making it the second largest planet in the solar system. Saturn is also the least dense planet in the solar system. It is less dense than water. What would happen if you had a large enough bathtub to put Saturn in? Saturn would float! Saturn orbits the Sun once about every 30 Earth years. Like Jupiter, Saturn is made mostly of hydrogen and helium gases in the outer layers and liquids at greater depths. The upper atmosphere has clouds in bands of different colors. These rotate rapidly around the planet, but there seems to be less turbulence and fewer storms on Saturn than on Jupiter. One interesting phenomenon that has been observed in the storms on Saturn is the presence of thunder and lightning (see video, below). The planet likely has a small rocky and metallic core. This image of Saturn and its rings is a composite of pictures taken by the Cassini orbiter in 2008 | text | null |
L_0294 | saturn | T_1646 | In 1610, Galileo first observed Saturns rings with his telescope, but he thought they might be two large moons, one on either side of the planet. In 1659, the Dutch astronomer Christian Huygens realized that the features were rings (Figure 1.2). Saturns rings circle the planets equator and appear tilted because Saturn itself is tilted about 27 degrees. The rings do not touch the planet. The Voyager 1 and 2 spacecraft in 1980 and 1981 sent back detailed pictures of Saturn, its rings, and some of its moons. Saturns rings are made of particles of water and ice, with some dust and rocks (Figure 1.3). There are several gaps in the rings that scientists think have originated because the material was cleared out by the gravitational pull within the rings, or by the gravitational forces of Saturn and of moons outside the rings. The rings were likely formed by the breakup of one of Saturns moons or from material that never accreted into the planet when Saturn originally formed. | text | null |
L_0294 | saturn | T_1647 | Most of Saturns moons are very small, and only seven are large enough for gravity to have made them spherical. Only Titan is larger than Earths Moon at about 1.5 times its size. Titan is even larger than the planet Mercury. Scientists are interested in Titan because its atmosphere is similar to what Earths was like before life developed. Nitrogen is dominant and methane is the second most abundant gas. Titan may have a layer of liquid water and ammonia under a layer of surface ice. Lakes of liquid methane (CH4 ) and ethane (C2 H6 ) are found on Titans surface. Although conditions are similar enough to those of early Earth for scientists to speculate that extremely A color-exaggerated mosaic of Saturn and its rings taken by Cassini as Saturn eclipses the Sun. A close-up of Saturns outer C ring show- ing areas with higher particle concentra- tion and gaps. This composite image compares Saturns largest moon, Titan (right) to Earth (left). Click image to the left or use the URL below. URL: | text | null |
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