lessonID
stringlengths 6
6
| lessonName
stringlengths 3
52
| ID
stringlengths 6
21
| content
stringlengths 10
6.57k
| media_type
stringclasses 2
values | path
stringlengths 28
76
⌀ |
|---|---|---|---|---|---|
L_0132 | early atmosphere and oceans | T_1070 | The early atmosphere was rich in water vapor from volcanic eruptions and comets. When Earth was cool enough, water vapor condensed and rain began to fall. The water cycle began. Over millions of years enough precipitation collected that the first oceans could have formed as early as 4.2 to 4.4 billion years ago. Dissolved minerals carried by stream runoff made the early oceans salty. What geological evidence could there be for the presence of an early ocean? Marine sedimentary rocks can be dated back about 4 billion years. By the Archean, the planet was covered with oceans and the atmosphere was full of water vapor, carbon dioxide, nitrogen, and smaller amounts of other gases. Click image to the left or use the URL below. URL: | text | null |
L_0132 | early atmosphere and oceans | T_1071 | When photosynthesis evolved and spread around the planet, oxygen was released in abundance. The addition of oxygen is what created Earths third atmosphere. This event, which occurred about 2.5 billion years ago, is sometimes called the oxygen catastrophe because so many organisms died. Although entire species died out and went extinct, this event is also called the Great Oxygenation Event because it was a great opportunity. The organisms that survived developed a use for oxygen through cellular respiration, the process by which cells can obtain energy from organic molecules. This opened up many opportunities for organisms to evolve to fill different niches and many new types of organisms first appeared on Earth. | text | null |
L_0132 | early atmosphere and oceans | T_1072 | What evidence do scientists have that large quantities of oxygen entered the atmosphere? The iron contained in the rocks combined with the oxygen to form reddish iron oxides. By the beginning of the Proterozoic, banded-iron formations (BIFs) were forming. Banded-iron formations display alternating bands of iron oxide and iron-poor chert that probably represent a seasonal cycle of an aerobic and an anaerobic environment. The oldest BIFs are 3.7 billion years old, but they are very common during the Great Oxygenation Event 2.4 billion years ago (Figure 1.2). By 1.8 billion years ago, the amount of BIF declined. In recent times, the iron in these formations has been mined, and that explains the location of the auto industry in the upper Midwest. | text | null |
L_0132 | early atmosphere and oceans | T_1073 | With more oxygen in the atmosphere, ultraviolet radiation could create ozone. With the formation of an ozone layer to protect the surface of the Earth from UV radiation, more complex life forms could evolve. Banded-iron formation. Click image to the left or use the URL below. URL: | text | null |
L_0133 | earth history and clues from fossils | T_1074 | Fossils are our best form of evidence about Earth history, including the history of life. Along with other geological evidence from rocks and structures, fossils even give us clues about past climates, the motions of plates, and other major geological events. Since the present is the key to the past, what we know about a type of organism that lives today can be applied to past environments. | text | null |
L_0133 | earth history and clues from fossils | T_1075 | That life on Earth has changed over time is well illustrated by the fossil record. Fossils in relatively young rocks resemble animals and plants that are living today. In general, fossils in older rocks are less similar to modern organisms. We would know very little about the organisms that came before us if there were no fossils. Modern technology has allowed scientists to reconstruct images and learn about the biology of extinct animals like dinosaurs! | text | null |
L_0133 | earth history and clues from fossils | T_1076 | By knowing something about the type of organism the fossil was, geologists can determine whether the region was terrestrial (on land) or marine (underwater) or even if the water was shallow or deep. The rock may give clues to whether the rate of sedimentation was slow or rapid. The amount of wear and fragmentation of a fossil allows scientists to learn about what happened to the region after the organism died; for example, whether it was exposed to wave action. | text | null |
L_0133 | earth history and clues from fossils | T_1077 | The presence of marine organisms in a rock indicates that the region where the rock was deposited was once marine. Sometimes fossils of marine organisms are found on tall mountains indicating that rocks that formed on the seabed were uplifted. | text | null |
L_0133 | earth history and clues from fossils | T_1078 | By knowing something about the climate a type of organism lives in now, geologists can use fossils to decipher the climate at the time the fossil was deposited. For example, coal beds form in tropical environments but ancient coal beds are found in Antarctica. Geologists know that at that time the climate on the Antarctic continent was much warmer. Recall from the chapter Plate Tectonics that Wegener used the presence of coal beds in Antarctica as one of the lines of evidence for continental drift. | text | null |
L_0133 | earth history and clues from fossils | T_1079 | An index fossil can be used to identify a specific period of time. Organisms that make good index fossils are distinctive, widespread, and lived briefly. Their presence in a rock layer can be used to identify rocks that were deposited at that period of time over a large area. The fossil of a juvenile mammoth found near downtown San Jose California reveals an enormous amount about these majestic creatures: what they looked like, how they lived, and what the environment of the Bay Area was like so long ago. | text | null |
L_0140 | earths core | T_1099 | At the planets center lies a dense metallic core. Scientists know that the core is metal because: 1. The density of Earths surface layers is much less than the overall density of the planet, as calculated from the planets rotation. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85% iron metal with nickel metal making up much of the remaining 15%. 2. Metallic meteorites are thought to be representative of the core. The 85% iron/15% nickel calculation above is also seen in metallic meteorites (Figure 1.1). If Earths core were not metal, the planet would not have a magnetic field. Metals such as iron are magnetic, but rock, which makes up the mantle and crust, is not. Scientists know that the outer core is liquid and the inner core is solid because: 1. S-waves do not go through the outer core. 2. The strong magnetic field is caused by convection in the liquid outer core. Convection currents in the outer core are due to heat from the even hotter inner core. The heat that keeps the outer core from solidifying is produced by the breakdown of radioactive elements in the inner core. Click image to the left or use the URL below. URL: | text | null |
L_0142 | earths interior material | T_1103 | It wasnt always known that fossils were parts of living organisms. In 1666, a young doctor named Nicholas Steno dissected the head of an enormous great white shark that had been caught by fisherman near Florence, Italy. Steno was struck by the resemblance of the sharks teeth to fossils found in inland mountains and hills (Figure ??). Most people at the time did not believe that fossils were once part of living creatures. Authors in that day thought that the fossils of marine animals found in tall mountains, miles from any ocean could be explained in one of two ways: The shells were washed up during the Biblical flood. (This explanation could not account for the fact that fossils were not only found on mountains, but also within mountains, in rocks that had been quarried from deep below Earths surface.) The fossils formed within the rocks as a result of mysterious forces. But for Steno, the close resemblance between fossils and modern organisms was impossible to ignore. Instead of invoking supernatural forces, Steno concluded that fossils were once parts of living creatures. | text | null |
L_0142 | earths interior material | T_1104 | A fossil is any remains or traces of an ancient organism. Fossils include body fossils, left behind when the soft parts have decayed away, and trace fossils, such as burrows, tracks, or fossilized coprolites (feces) as seen above. Collections of fossils are known as fossil assemblages. | text | null |
L_0142 | earths interior material | T_1105 | Becoming a fossil isnt easy. Only a tiny percentage of the organisms that have ever lived become fossils. Why do you think only a tiny percentage of living organisms become fossils after death? Think about an antelope that dies on the African plain (Figure ??). Most of its body is eaten by hyenas and other scavengers and the remaining flesh is devoured by insects and bacteria. Only bones are left behind. As the years go by, the bones are scattered and fragmented into small pieces, eventually turning into dust. The remaining nutrients return to the soil. This antelope will not be preserved as a fossil. Is it more likely that a marine organism will become a fossil? When clams, oysters, and other shellfish die, the soft parts quickly decay, and the shells are scattered. In shallow water, wave action grinds them into sand-sized pieces. The shells are also attacked by worms, sponges, and other animals (Figure ??). How about a soft bodied organism? Will a creature without hard shells or bones become a fossil? There is virtually no fossil record of soft bodied organisms such as jellyfish, worms, or slugs. Insects, which are by far the most common land animals, are only rarely found as fossils (Figure ??). | text | null |
L_0142 | earths interior material | T_1106 | Despite these problems, there is a rich fossil record. How does an organism become fossilized? | text | null |
L_0142 | earths interior material | T_1107 | Usually its only the hard parts that are fossilized. The fossil record consists almost entirely of the shells, bones, or other hard parts of animals. Mammal teeth are much more resistant than other bones, so a large portion of the mammal fossil record consists of teeth. The shells of marine creatures are common also. | text | null |
L_0142 | earths interior material | T_1108 | Quick burial is essential because most decay and fragmentation occurs at the surface. Marine animals that die near a river delta may be rapidly buried by river sediments. A storm at sea may shift sediment on the ocean floor, covering a body and helping to preserve its skeletal remains (Figure ??). Quick burial is rare on land, so fossils of land animals and plants are less common than marine fossils. Land organisms can be buried by mudslides, volcanic ash, or covered by sand in a sandstorm (Figure ??). Skeletons can be covered by mud in lakes, swamps, or bogs. | text | null |
L_0142 | earths interior material | T_1109 | Unusual circumstances may lead to the preservation of a variety of fossils, as at the La Brea Tar Pits in Los Angeles, California. Although the animals trapped in the La Brea Tar Pits probably suffered a slow, miserable death, their bones were preserved perfectly by the sticky tar. (Figure ??). In spite of the difficulties of preservation, billions of fossils have been discovered, examined, and identified by thousands of scientists. The fossil record is our best clue to the history of life on Earth, and an important indicator of past climates and geological conditions as well. | text | null |
L_0142 | earths interior material | T_1110 | Some rock beds contain exceptional fossils or fossil assemblages. Two of the most famous examples of soft organism preservation are from the 505 million-year-old Burgess Shale in Canada (Figure ??). The 145 million-year-old Solnhofen Limestone in Germany has fossils of soft body parts that are not normally preserved (Figure ??). | text | null |
L_0142 | earths interior material | T_1111 | Use this resource to answer the questions that follow. Click image to the left for more content. 1. What are fossils? 2. What type of rocks are fossils found in? 3. What are sediments? 4. Explain how a fossil is created. 5. What factors have exposed sedimentary rock? | text | null |
L_0144 | earths magnetic field | T_1114 | Earth is surrounded by a magnetic field (Figure 1.1) that behaves as if the planet had a gigantic bar magnet inside of it. Earths magnetic field also has a north and south pole. The magnetic field arises from the convection of molten iron and nickel metals in Earths liquid outer core. | text | null |
L_0144 | earths magnetic field | T_1115 | Many times during Earth history, even relatively recent Earth history, the planets magnetic field has flipped. That is, the north pole becomes the south pole and the south pole becomes the north pole. Scientists are not sure why this happens. One hypothesis is that the convection that drives the magnetic field becomes chaotic and then reverses itself. Another hypothesis is that an external event, such as an asteroid impact, disrupts motions in the core and causes the reversal. The first hypothesis is supported by computer models, but the second does not seem to be supported by much data. There is little correlation between impact events and magnetic reversals. Click image to the left or use the URL below. URL: Earths magnetic field is like a bar magnet resides in the center of the planet. | text | null |
L_0146 | earths shape | T_1119 | Earth is a sphere or, more correctly, an oblate spheroid, which is a sphere that is a bit squished down at the poles and bulges a bit at the Equator. To be more technical, the minor axis (the diameter through the poles) is smaller than the major axis (the diameter through the Equator). Half of the sphere is a hemisphere. North of the Equator is the northern hemisphere and south of the Equator is the southern hemisphere. Eastern and western hemispheres are also designated. What evidence is there that Earth is spherical? What evidence was there before spaceships and satellites? Try to design an experiment involving a ship and the ocean to show Earth is round. If you are standing on the shore and a ship is going out to sea, the ship gets smaller as it moves further away from you. The ships bottom also starts to disappear as the vessel goes around the arc of the planet (Figure 1.1). There are many other ways that early scientists and mariners knew that Earth was not flat. The Sun and the other planets of the solar system are also spherical. Larger satellites, those that have enough mass for their gravitational attraction to have made them round, are spherical as well. Earths actual shape is not spherical but an oblate spheroid. The planet bulges around the equator due to mass collecting in the middle due to rotational momentum. | text | null |
L_0148 | eclipses | T_1123 | A solar eclipse occurs when the new Moon passes directly between the Earth and the Sun (Figure 1.1). This casts a shadow on the Earth and blocks Earths view of the Sun. A total solar eclipse occurs when the Moons shadow completely blocks the Sun (Figure 1.2). When only a portion of the Sun is out of view, it is called a partial solar eclipse. Solar eclipses are rare and usually only last a few minutes because the Moon casts only a small shadow (Figure 1.3). As the Sun is covered by the Moons shadow, it will actually get cooler outside. Birds may begin to sing, and stars will become visible in the sky. During a solar eclipse, the corona and solar prominences can be seen. A solar eclipse occurs when the Moon passes between Earth and the Sun in such a way that the Sun is either partially or totally hidden from view. Some people, including some scientists, chase eclipses all over the world to learn or just observe this amazing phenomenon. A solar eclipse shown as a series of pho- tos. Click image to the left or use the URL below. URL: | text | null |
L_0148 | eclipses | T_1123 | A solar eclipse occurs when the new Moon passes directly between the Earth and the Sun (Figure 1.1). This casts a shadow on the Earth and blocks Earths view of the Sun. A total solar eclipse occurs when the Moons shadow completely blocks the Sun (Figure 1.2). When only a portion of the Sun is out of view, it is called a partial solar eclipse. Solar eclipses are rare and usually only last a few minutes because the Moon casts only a small shadow (Figure 1.3). As the Sun is covered by the Moons shadow, it will actually get cooler outside. Birds may begin to sing, and stars will become visible in the sky. During a solar eclipse, the corona and solar prominences can be seen. A solar eclipse occurs when the Moon passes between Earth and the Sun in such a way that the Sun is either partially or totally hidden from view. Some people, including some scientists, chase eclipses all over the world to learn or just observe this amazing phenomenon. A solar eclipse shown as a series of pho- tos. Click image to the left or use the URL below. URL: | text | null |
L_0148 | eclipses | T_1124 | A lunar eclipse occurs when the full moon moves through Earths shadow, which only happens when Earth is between the Moon and the Sun and all three are lined up in the same plane, called the ecliptic (Figure 1.4). In an eclipse, Earths shadow has two distinct parts: the umbra and the penumbra. The umbra is the inner, cone-shaped part of the shadow, in which all of the light has been blocked. The penumbra is the outer part of Earths shadow where only part of the light is blocked. In the penumbra, the light is dimmed but not totally absent. A total lunar eclipse occurs when the Moon travels completely in Earths umbra. During a partial lunar eclipse, only a portion of the Moon enters Earths umbra. Earths shadow is large enough that a lunar eclipse lasts for hours and can be seen by any part of Earth with a view of the Moon at the time of the eclipse (Figure 1.5). A lunar eclipse does not occur every month because Moons orbit is inclined 5-degrees to Earths orbit, so the two bodies are not in the same plane every month. | text | null |
L_0148 | eclipses | T_1124 | A lunar eclipse occurs when the full moon moves through Earths shadow, which only happens when Earth is between the Moon and the Sun and all three are lined up in the same plane, called the ecliptic (Figure 1.4). In an eclipse, Earths shadow has two distinct parts: the umbra and the penumbra. The umbra is the inner, cone-shaped part of the shadow, in which all of the light has been blocked. The penumbra is the outer part of Earths shadow where only part of the light is blocked. In the penumbra, the light is dimmed but not totally absent. A total lunar eclipse occurs when the Moon travels completely in Earths umbra. During a partial lunar eclipse, only a portion of the Moon enters Earths umbra. Earths shadow is large enough that a lunar eclipse lasts for hours and can be seen by any part of Earth with a view of the Moon at the time of the eclipse (Figure 1.5). A lunar eclipse does not occur every month because Moons orbit is inclined 5-degrees to Earths orbit, so the two bodies are not in the same plane every month. | text | null |
L_0150 | effect of latitude on climate | T_1127 | Many factors influence the climate of a region. The most important factor is latitude because different latitudes receive different amounts of solar radiation. The Equator receives the most solar radiation. Days are equally long year-round and the Sun is just about directly overhead at midday. The polar regions receive the least solar radiation. The night lasts six months during the winter. Even in summer, the Sun never rises very high in the sky. Sunlight filters through a thick wedge of atmosphere, making the sunlight much less intense. The high albedo, because of ice and snow, reflects a good portion of the Suns light. | text | null |
L_0150 | effect of latitude on climate | T_1128 | Its easy to see the difference in temperature at different latitudes in the Figure 1.1. But temperature is not completely correlated with latitude. There are many exceptions. For example, notice that the western portion of South America The maximum annual temperature of the Earth, showing a roughly gradual temperature gradient from the low to the high latitudes. has relatively low temperatures due to the Andes Mountains. The Rocky Mountains in the United States also have lower temperatures due to high altitudes. Western Europe is warmer than it should be due to the Gulf Stream. Click image to the left or use the URL below. URL: | text | null |
L_0151 | effects of air pollution on human health | T_1129 | Human health suffers in locations with high levels of air pollution. | text | null |
L_0151 | effects of air pollution on human health | T_1130 | Different pollutants have different health effects: Lead is the most common toxic material and is responsible for lead poisoning. Carbon monoxide can kill people in poorly ventilated spaces, such as tunnels. Nitrogen and sulfur-oxides cause lung disease and increased rates of asthma, emphysema, and viral infections such as the flu. Ozone damages the human respiratory system, causing lung disease. High ozone levels are also associated with increased heart disease and cancer. Particulates enter the lungs and cause heart or lung disease. When particulate levels are high, asthma attacks are more common. By some estimates, 30,000 deaths a year in the United States are caused by fine particle pollution. | text | null |
L_0151 | effects of air pollution on human health | T_1131 | Many but not all cases of asthma can be linked to air pollution. During the 1996 Olympic Games, Atlanta, Georgia, closed off their downtown to private vehicles. This action decreased ozone levels by 28%. At the same time, there were 40% fewer hospital visits for asthma. Can scientists conclude without a shadow of a doubt that the reduction in ozone caused the reduction in hospital visits? What could they do to make that determination? Lung cancer among people who have never smoked is around 15% and is increasing. One study showed that the risk of being afflicted with lung cancer increases directly with a persons exposure to air pollution (Figure 1.1). The study concluded that no level of air pollution should be considered safe. Exposure to smog also increased the risk of dying from any cause, including heart disease. One study found that in the United States, children develop asthma at more than twice the rate of two decades ago and at four times the rate of children in Canada. Adults also suffer from air pollution-related illnesses that include lung disease, heart disease, lung cancer, and weakened immune systems. The asthma rate worldwide is rising 20% to 50% every decade. | text | null |
L_0154 | electromagnetic energy in the atmosphere | T_1139 | Energy travels through space or material. This is obvious when you stand near a fire and feel its warmth or when you pick up the handle of a metal pot even though the handle is not sitting directly on the hot stove. Invisible energy waves can travel through air, glass, and even the vacuum of outer space. These waves have electrical and magnetic properties, so they are called electromagnetic waves. The transfer of energy from one object to another through electromagnetic waves is known as radiation. Different wavelengths of energy create different types of electromagnetic waves (Figure 1.1). The wavelengths humans can see are known as visible light. When viewed together, all of the wavelengths of visible light appear white. But a prism or water droplets can break the white light into different wavelengths so that separate colors appear (Figure 1.2). What objects can you think of that radiate visible light? Two include the Sun and a light bulb. The longest wavelengths of visible light appear red. Infrared wavelengths are longer than visible red. Snakes can see infrared energy. We feel infrared energy as heat. Wavelengths that are shorter than violet are called ultraviolet. Can you think of some objects that appear to radiate visible light, but actually do not? The Moon and the planets do not emit light of their own; they reflect the light of the Sun. Reflection is when light (or another wave) bounces back from a surface. Albedo is a measure of how well a surface reflects light. A surface with high albedo reflects a large percentage of light. A snow field has high albedo. One important fact to remember is that energy cannot be created or destroyed it can only be changed from one form to another. This is such a fundamental fact of nature that it is a law: the law of conservation of energy. In photosynthesis, for example, plants convert solar energy into chemical energy that they can use. They do not create new energy. When energy is transformed, some nearly always becomes heat. Heat transfers between materials easily, from warmer objects to cooler ones. If no more heat is added, eventually all of a material will reach the same temperature. | text | null |
L_0154 | electromagnetic energy in the atmosphere | T_1139 | Energy travels through space or material. This is obvious when you stand near a fire and feel its warmth or when you pick up the handle of a metal pot even though the handle is not sitting directly on the hot stove. Invisible energy waves can travel through air, glass, and even the vacuum of outer space. These waves have electrical and magnetic properties, so they are called electromagnetic waves. The transfer of energy from one object to another through electromagnetic waves is known as radiation. Different wavelengths of energy create different types of electromagnetic waves (Figure 1.1). The wavelengths humans can see are known as visible light. When viewed together, all of the wavelengths of visible light appear white. But a prism or water droplets can break the white light into different wavelengths so that separate colors appear (Figure 1.2). What objects can you think of that radiate visible light? Two include the Sun and a light bulb. The longest wavelengths of visible light appear red. Infrared wavelengths are longer than visible red. Snakes can see infrared energy. We feel infrared energy as heat. Wavelengths that are shorter than violet are called ultraviolet. Can you think of some objects that appear to radiate visible light, but actually do not? The Moon and the planets do not emit light of their own; they reflect the light of the Sun. Reflection is when light (or another wave) bounces back from a surface. Albedo is a measure of how well a surface reflects light. A surface with high albedo reflects a large percentage of light. A snow field has high albedo. One important fact to remember is that energy cannot be created or destroyed it can only be changed from one form to another. This is such a fundamental fact of nature that it is a law: the law of conservation of energy. In photosynthesis, for example, plants convert solar energy into chemical energy that they can use. They do not create new energy. When energy is transformed, some nearly always becomes heat. Heat transfers between materials easily, from warmer objects to cooler ones. If no more heat is added, eventually all of a material will reach the same temperature. | text | null |
L_0155 | energy conservation | T_1140 | Everyone can reduce their use of energy resources and the pollution the resources cause by conserving energy. Conservation means saving resources by using them more efficiently, using less of them, or not using them at all. You can read below about some of the ways you can conserve energy on the road and in the home. | text | null |
L_0155 | energy conservation | T_1141 | Much of the energy used in the U.S. is used for transportation. You can conserve transportation energy in several ways. For example, you can: plan ahead to avoid unnecessary trips. take public transit such as subways (see Figure 1.1) instead of driving. drive an energy-efficient vehicle when driving is the only way to get there. Q: What are some other ways you could save energy in transportation? A: You could carpool to save transportation energy. Even if you carpool with just one other person, thats one less vehicle on the road. For short trips, you could ride a bike or walk to you destination. The extra exercise is another benefit of using your own muscle power to get where you need to go. | text | null |
L_0155 | energy conservation | T_1142 | Many people waste energy at home, so a lot of energy can be saved there as well. What can you do to conserve energy? You can: turn off lights and unplug appliances and other electrical devices when not in use. use energy-efficient light bulbs and appliances. turn the thermostat down in winter and up in summer. Q: How can you tell which light bulbs and appliances use less energy? | text | null |
L_0155 | energy conservation | T_1142 | Many people waste energy at home, so a lot of energy can be saved there as well. What can you do to conserve energy? You can: turn off lights and unplug appliances and other electrical devices when not in use. use energy-efficient light bulbs and appliances. turn the thermostat down in winter and up in summer. Q: How can you tell which light bulbs and appliances use less energy? | text | null |
L_0156 | energy from biomass | T_1143 | Biomass is the material that comes from plants and animals that were recently living. Biomass can be burned directly, such as setting fire to wood. For as long as humans have had fire, people have used biomass for heating and cooking. People can also process biomass to make fuel, called biofuel. Biofuel can be created from crops, such as corn or Biofuels, such as ethanol, are added to gasoline to cut down the amount of fossil fuels that are used. algae, and processed for use in a car (Figure 1.1). The advantage to biofuels is that they burn more cleanly than fossil fuels. As a result, they create less pollution and less carbon dioxide. Organic material, like almond shells, can be made into electricity. Biomass power is a great use of wastes and is more reliable than other renewable energy sources, but harvesting biomass energy uses energy and biomass plants produce pollutants including greenhouse gases. Cow manure can have a second life as a source of methane gas, which can be converted to electricity. Not only that food scraps can also be converted into green energy. Food that is tossed out produces methane, a potent greenhouse gas. But that methane from leftovers can be harnessed and used as fuel. Sounds like a win-win situation. | text | null |
L_0156 | energy from biomass | T_1144 | In many instances, the amount of energy, fertilizer, and land needed to produce the crops used make biofuels mean that they often produce very little more energy than they consume. The fertilizers and pesticides used to grow the crops run off and become damaging pollutants in nearby water bodies or in the oceans. To generate biomass energy, break down the cell walls of plants to release the sugars and then ferment those sugars to create fuel. Corn is a very inefficient source; scientists are looking for much better sources of biomass energy. | text | null |
L_0156 | energy from biomass | T_1145 | Research is being done into alternative crops for biofuels. A very promising alternative is algae. Growing algae requires much less land and energy than crops. Algae can be grown in locations that are not used for other things, like in desert areas where other crops are not often grown. Algae can be fed agricultural and other waste so valuable resources are not used. Much research is being done to bring these alternative fuels to market. Many groups are researching the use of algae for fuel. Many people think that the best source of biomass energy for the future is algae. Compared to corn, algae is not a food crop, it can grow in many places, its much easier to convert to a usable fuel, and its carbon neutral. | text | null |
L_0157 | energy use | T_1146 | Look at the circle graph in the Figure 1.1. It shows that oil is the single most commonly used energy resource in the U.S., followed by natural gas, and then by coal. All of these energy resources are nonrenewable. Nonrenewable resources are resources that are limited in supply and cannot be replaced as quickly as they are used up. Renewable resources, in contrast, provide only 8 percent of all energy used in the U.S. Renewable resources are natural resources that can be replaced in a relatively short period of time or are virtually limitless in supply. They include solar energy from sunlight, geothermal energy from under Earths surface, wind, biomass (from once-living things or their wastes), and hydropower (from running water). | text | null |
L_0157 | energy use | T_1147 | People in the U.S. use far more energyespecially energy from oilthan people in any other nation. The bar graph in the Figure 1.2 compares the amount of oil used by the top ten oil-using nations. The U.S. uses more oil than several other top-ten countries combined. If you also consider the population size in these countries, the differences are even more stunning. The average person in the U.S. uses a whopping 23 barrels of oil a year! In comparison, the average person in India or China uses just 1 or 2 barrels of oil a year. Q: How does the use of oil and other fossil fuels relate to pollution? A: Greater use of oil and other fossil fuels causes more pollution. | text | null |
L_0157 | energy use | T_1147 | People in the U.S. use far more energyespecially energy from oilthan people in any other nation. The bar graph in the Figure 1.2 compares the amount of oil used by the top ten oil-using nations. The U.S. uses more oil than several other top-ten countries combined. If you also consider the population size in these countries, the differences are even more stunning. The average person in the U.S. uses a whopping 23 barrels of oil a year! In comparison, the average person in India or China uses just 1 or 2 barrels of oil a year. Q: How does the use of oil and other fossil fuels relate to pollution? A: Greater use of oil and other fossil fuels causes more pollution. | text | null |
L_0158 | environmental impacts of mining | T_1148 | Although mining provides people with many needed resources, the environmental costs can be high. Surface mining clears the landscape of trees and soil, and nearby streams and lakes are inundated with sediment. Pollutants from the mined rock, such as heavy metals, enter the sediment and water system. Acids flow from some mine sites, changing the composition of nearby waterways (Figure 1.1). U.S. law has changed in recent decades so that a mine region must be restored to its natural state, a process called reclamation. This is not true of older mines. Pits may be refilled or reshaped and vegetation planted. Pits may be allowed to fill with water and become lakes or may be turned into landfills. Underground mines may be sealed off or left open as homes for bats. Click image to the left or use the URL below. URL: Acid drainage from a surface coal mine in Missouri. | text | null |
L_0161 | exoplanets | T_1158 | Since the early 1990s, astronomers have discovered other solar systems, with planets orbiting stars other than our own Sun. These are called "extrasolar planets" or simply exoplanets (see Figure 1.1). Exoplanets are not in our solar system, but are found in other solar systems. Some extrasolar planets have been directly imaged, but most have been discovered by indirect methods. One technique involves detecting the very slight motion of a star periodically moving toward and away from us along our line-of-sight (also known as a stars "radial velocity"). This periodic motion can be attributed to the gravitational pull of a planet or, sometimes, another star orbiting the star. A planet may also be identified by measuring a stars brightness over time. A temporary, periodic decrease in light emitted from a star can occur when a planet crosses in front of, or "transits," the star it is orbiting, momentarily blocking out some of the starlight. More than 1800 extrasolar planets have been identified and confirmed and the rate of discovery is increasing rapidly. Click image to the left or use the URL below. URL: | text | null |
L_0162 | expansion of the universe | T_1159 | After discovering that there are galaxies beyond the Milky Way, Edwin Hubble went on to measure the distance to hundreds of other galaxies. His data would eventually show how the universe is changing, and would even yield clues as to how the universe formed. | text | null |
L_0162 | expansion of the universe | T_1160 | If you look at a star through a prism, you will see a spectrum, or a range of colors through the rainbow. The spectrum will have specific dark bands where elements in the star absorb light of certain energies. By examining the arrangement of these dark absorption lines, astronomers can determine the composition of elements that make up a distant star. In fact, the element helium was first discovered in our Sun not on Earth by analyzing the absorption lines in the spectrum of the Sun. While studying the spectrum of light from distant galaxies, astronomers noticed something strange. The dark lines in the spectrum were in the patterns they expected, but they were shifted toward the red end of the spectrum, as shown in Figure 1.1. This shift of absorption bands toward the red end of the spectrum is known as redshift. Redshift is a shift in absorption bands toward the red end of the spectrum. What could make the absorption bands of a star shift toward the red? Redshift occurs when the light source is moving away from the observer or when the space between the observer and the source is stretched. What does it mean that stars and galaxies are redshifted? When astronomers see redshift in the light from a galaxy, they know that the galaxy is moving away from Earth. If galaxies were moving randomly, would some be redshifted but others be blueshifted? Of course. Since almost every galaxy in the universe has a redshift, almost every galaxy is moving away from Earth. Click image to the left or use the URL below. URL: | text | null |
L_0162 | expansion of the universe | T_1161 | Edwin Hubble combined his measurements of the distances to galaxies with other astronomers measurements of redshift. From this data, he noticed a relationship, which is now called Hubbles Law: the farther away a galaxy is, the faster it is moving away from us. What could this mean about the universe? It means that the universe is expanding. Figure 1.2 shows a simplified diagram of the expansion of the universe. One way to picture this is to imagine a balloon covered with tiny dots to represent the galaxies. When you inflate the balloon, the dots slowly move away from each other because the rubber stretches in the space between them. If you were standing on one of the dots, you would see the other dots moving away from you. Also, the dots farther away from you on the balloon would move away faster than dots nearby. In this diagram of the expansion of the universe over time, the distance between galaxies gets bigger over time, although the size of each galaxy stays the same. An inflating balloon is only a rough analogy to the expanding universe for several reasons. One important reason is that the surface of a balloon has only two dimensions, while space has three dimensions. But space itself is stretching out between galaxies, just as the rubber stretches when a balloon is inflated. This stretching of space, which increases the distance between galaxies, is what causes the expansion of the universe. One other difference between the universe and a balloon involves the actual size of the galaxies. On a balloon, the dots will become larger in size as you inflate it. In the universe, the galaxies stay the same size; only the space between the galaxies increases. | text | null |
L_0165 | faults | T_1169 | A rock under enough stress will fracture. There may or may not be movement along the fracture. | text | null |
L_0165 | faults | T_1170 | If there is no movement on either side of a fracture, the fracture is called a joint. The rocks below show horizontal and vertical jointing. These joints formed when the confining stress was removed from the rocks as shown in (Figure | text | null |
L_0165 | faults | T_1171 | If the blocks of rock on one or both sides of a fracture move, the fracture is called a fault (Figure 1.2). Stresses along faults cause rocks to break and move suddenly. The energy released is an earthquake. How do you know theres a fault in this rock? Try to line up the same type of rock on either side of the lines that cut across them. One side moved relative to the other side, so you know the lines are a fault. Slip is the distance rocks move along a fault. Slip can be up or down the fault plane. Slip is relative, because there is usually no way to know whether both sides moved or only one. Faults lie at an angle to the horizontal surface of the Earth. That angle is called the faults dip. The dip defines which of two basic types a fault is. If the faults dip is inclined relative to the horizontal, the fault is a dip-slip fault (Figure 1.3). | text | null |
L_0165 | faults | T_1172 | There are two types of dip-slip faults. In a normal fault, the hanging wall drops down relative to the footwall. In a reverse fault, the footwall drops down relative to the hanging wall. This diagram illustrates the two types of dip-slip faults: normal faults and reverse faults. Imagine miners extracting a re- source along a fault. The hanging wall is where miners would have hung their lanterns. The footwall is where they would have walked. A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 1.4). At Chief Mountain in Montana, the upper rocks at the Lewis Overthrust are more than 1 billion years older than the lower rocks. How could this happen? Normal faults can be huge. They are responsible for uplifting mountain ranges in regions experiencing tensional stress. | text | null |
L_0165 | faults | T_1172 | There are two types of dip-slip faults. In a normal fault, the hanging wall drops down relative to the footwall. In a reverse fault, the footwall drops down relative to the hanging wall. This diagram illustrates the two types of dip-slip faults: normal faults and reverse faults. Imagine miners extracting a re- source along a fault. The hanging wall is where miners would have hung their lanterns. The footwall is where they would have walked. A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 1.4). At Chief Mountain in Montana, the upper rocks at the Lewis Overthrust are more than 1 billion years older than the lower rocks. How could this happen? Normal faults can be huge. They are responsible for uplifting mountain ranges in regions experiencing tensional stress. | text | null |
L_0165 | faults | T_1173 | A strike-slip fault is a dip-slip fault in which the dip of the fault plane is vertical. Strike-slip faults result from shear stresses. Imagine placing one foot on either side of a strike-slip fault. One block moves toward you. If that block moves toward your right foot, the fault is a right-lateral strike-slip fault; if that block moves toward your left foot, the fault is a left-lateral strike-slip fault (Figure 1.5). Californias San Andreas Fault is the worlds most famous strike-slip fault. It is a right-lateral strike slip fault (See opening image). People sometimes say that California will fall into the ocean someday, which is not true. Strike-slip faults. Click image to the left or use the URL below. URL: | text | null |
L_0167 | flooding | T_1179 | Floods usually occur when precipitation falls more quickly than water can be absorbed into the ground or carried away by rivers or streams. Waters may build up gradually over a period of weeks, when a long period of rainfall or snowmelt fills the ground with water and raises stream levels. Extremely heavy rains across the Midwestern U.S. in April 2011 led to flooding of the rivers in the Mississippi River basin in May 2011 (Figures 1.1 and 1.2). Click image to the left or use the URL below. URL: This map shows the accumulated rainfall across the U.S. in the days from April 22 to April 29, 2011. Record flow in the Ohio and Mississippi Rivers has to go somewhere. Normal spring river levels are shown in 2010. The flooded region in the image from May 3, 2011 is the New Madrid Floodway, where overflow water is meant to go. 2011 is the first time since 1927 that this floodway was used. | text | null |
L_0167 | flooding | T_1179 | Floods usually occur when precipitation falls more quickly than water can be absorbed into the ground or carried away by rivers or streams. Waters may build up gradually over a period of weeks, when a long period of rainfall or snowmelt fills the ground with water and raises stream levels. Extremely heavy rains across the Midwestern U.S. in April 2011 led to flooding of the rivers in the Mississippi River basin in May 2011 (Figures 1.1 and 1.2). Click image to the left or use the URL below. URL: This map shows the accumulated rainfall across the U.S. in the days from April 22 to April 29, 2011. Record flow in the Ohio and Mississippi Rivers has to go somewhere. Normal spring river levels are shown in 2010. The flooded region in the image from May 3, 2011 is the New Madrid Floodway, where overflow water is meant to go. 2011 is the first time since 1927 that this floodway was used. | text | null |
L_0167 | flooding | T_1180 | Flash floods are sudden and unexpected, taking place when very intense rains fall over a very brief period (Figure streambed. A 2004 flash flood in England devastated two villages when 3-1/2 inches of rain fell in 60 minutes. Pictured here is some of the damage from the flash flood. Click image to the left or use the URL below. URL: | text | null |
L_0167 | flooding | T_1181 | Heavily vegetated lands are less likely to experience flooding. Plants slow down water as it runs over the land, giving it time to enter the ground. Even if the ground is too wet to absorb more water, plants still slow the waters passage and increase the time between rainfall and the waters arrival in a stream; this could keep all the water falling over a region from hitting the stream at once. Wetlands act as a buffer between land and high water levels and play a key role in minimizing the impacts of floods. Flooding is often more severe in areas that have been recently logged. | text | null |
L_0167 | flooding | T_1182 | People try to protect areas that might flood with dams, and dams are usually very effective. But high water levels sometimes cause a dam to break and then flooding can be catastrophic. People may also line a river bank with levees, high walls that keep the stream within its banks during floods. A levee in one location may just force the high water up or downstream and cause flooding there. The New Madrid Overflow in the Figure 1.2 was created with the recognition that the Mississippi River sometimes simply cannot be contained by levees and must be allowed to flood. | text | null |
L_0167 | flooding | T_1183 | Within the floodplain of the Nile, soils are fertile enough for productive agriculture. Beyond this, infertile desert soils prevent viable farming. Not all the consequences of flooding are negative. Rivers deposit new nutrient-rich sediments when they flood, so floodplains have traditionally been good for farming. Flooding as a source of nutrients was important to Egyptians along the Nile River until the Aswan Dam was built in the 1960s. Although the dam protects crops and settlements from the annual floods, farmers must now use fertilizers to feed their cops. Floods are also responsible for moving large amounts of sediments about within streams. These sediments provide habitats for animals, and the periodic movement of sediment is crucial to the lives of several types of organisms. Plants and fish along the Colorado River, for example, depend on seasonal flooding to rearrange sand bars. | text | null |
L_0169 | folds | T_1186 | Rocks deforming plastically under compressive stresses crumple into folds. They do not return to their original shape. If the rocks experience more stress, they may undergo more folding or even fracture. You can see three types of folds. | text | null |
L_0169 | folds | T_1187 | A monocline is a simple bend in the rock layers so that they are no longer horizontal (see Figure 1.1 for an example). At Utahs Cockscomb, the rocks plunge downward in a monocline. What you see in the image appears to be a monocline. Are you certain it is a monocline? What else might it be? What would you have to do to figure it out? | text | null |
L_0169 | folds | T_1188 | Anticline: An anticline is a fold that arches upward. The rocks dip away from the center of the fold (Figure 1.2). The oldest rocks are at the center of an anticline and the youngest are draped over them. When rocks arch upward to form a circular structure, that structure is called a dome. If the top of the dome is sliced off, where are the oldest rocks located? | text | null |
L_0169 | folds | T_1189 | A syncline is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (Figure 1.3). When rocks bend downward in a circular structure, that structure is called a basin (Figure 1.4). If the rocks are exposed at the surface, where are the oldest rocks located? Click image to the left or use the URL below. URL: Anticlines are formations that have folded rocks upward. (a) Schematic of a syncline. (b) This syncline is in Rainbow Basin, California. Some folding can be fairly complicated. What do you see in the photo above? | text | null |
L_0169 | folds | T_1189 | A syncline is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (Figure 1.3). When rocks bend downward in a circular structure, that structure is called a basin (Figure 1.4). If the rocks are exposed at the surface, where are the oldest rocks located? Click image to the left or use the URL below. URL: Anticlines are formations that have folded rocks upward. (a) Schematic of a syncline. (b) This syncline is in Rainbow Basin, California. Some folding can be fairly complicated. What do you see in the photo above? | text | null |
L_0169 | folds | T_1189 | A syncline is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (Figure 1.3). When rocks bend downward in a circular structure, that structure is called a basin (Figure 1.4). If the rocks are exposed at the surface, where are the oldest rocks located? Click image to the left or use the URL below. URL: Anticlines are formations that have folded rocks upward. (a) Schematic of a syncline. (b) This syncline is in Rainbow Basin, California. Some folding can be fairly complicated. What do you see in the photo above? | text | null |
L_0169 | folds | T_1189 | A syncline is a fold that bends downward. The youngest rocks are at the center and the oldest are at the outside (Figure 1.3). When rocks bend downward in a circular structure, that structure is called a basin (Figure 1.4). If the rocks are exposed at the surface, where are the oldest rocks located? Click image to the left or use the URL below. URL: Anticlines are formations that have folded rocks upward. (a) Schematic of a syncline. (b) This syncline is in Rainbow Basin, California. Some folding can be fairly complicated. What do you see in the photo above? | text | null |
L_0170 | formation of earth | T_1190 | Earth formed at the same time as the other planets. The history of Earth is part of the history of the Solar System. | text | null |
L_0170 | formation of earth | T_1191 | Earth came together (accreted) from the cloud of dust and gas known as the solar nebula nearly 4.6 billion years ago, the same time the Sun and the rest of the solar system formed. Gravity caused small bodies of rock and metal orbiting the proto-Sun to smash together to create larger bodies. Over time, the planetoids got larger and larger until they became planets. | text | null |
L_0170 | formation of earth | T_1192 | When Earth first came together it was really hot, hot enough to melt the metal elements that it contained. Earth was so hot for three reasons: Gravitational contraction: As small bodies of rock and metal accreted, the planet grew larger and more massive. Gravity within such an enormous body squeezes the material in its interior so hard that the pressure swells. As Earths internal pressure grew, its temperature also rose. Radioactive decay: Radioactive decay releases heat, and early in the planets history there were many ra- dioactive elements with short half lives. These elements long ago decayed into stable materials, but they were responsible for the release of enormous amounts of heat in the beginning. Bombardment: Ancient impact craters found on the Moon and inner planets indicate that asteroid impacts were common in the early solar system. Earth was struck so much in its first 500 million years that the heat was intense. Very few large objects have struck the planet in the past many hundreds of millions of year. | text | null |
L_0170 | formation of earth | T_1193 | When Earth was entirely molten, gravity drew denser elements to the center and lighter elements rose to the surface. The separation of Earth into layers based on density is known as differentiation. The densest material moved to the center to create the planets dense metallic core. Materials that are intermediate in density became part of the mantle (Figure 1.1). | text | null |
L_0170 | formation of earth | T_1194 | Lighter materials accumulated at the surface of the mantle to become the earliest crust. The first crust was probably basaltic, like the oceanic crust is today. Intense heat from the early core drove rapid and vigorous mantle convection so that crust quickly recycled into the mantle. The recycling of basaltic crust was so effective that no remnants of it are found today. | text | null |
L_0170 | formation of earth | T_1195 | There is not much material to let us know about the earliest days of our planet Earth. What there is comes from three sources: (1) zircon crystals, the oldest materials found on Earth, which show that the age of the earliest crust formed at least 4.4 billion years ago; (2) meteorites that date from the beginning of the solar system, to nearly 4.6 billion years ago (Figure 1.2); and (3) lunar rocks, which represent the early days of the Earth-Moon system as far back as 4.5 billion years ago. | text | null |
L_0171 | formation of the moon | T_1196 | One of the most unique features of planet Earth is its large Moon. Unlike the only other natural satellites orbiting an inner planet, those of Mars, the Moon is not a captured asteroid. Understanding the Moons birth and early history reveals a great deal about Earths early days. | text | null |
L_0171 | formation of the moon | T_1197 | To determine how the Moon formed, scientists had to account for several lines of evidence: The Moon is large; not much smaller than the smallest planet, Mercury. Earth and Moon are very similar in composition. Moons surface is 4.5 billion years old, about the same as the age of the solar system. For a body its size and distance from the Sun, the Moon has very little core; Earth has a fairly large core. The oxygen isotope ratios of Earth and Moon indicate that they originated in the same part of the solar system. Earth has a faster spin than it should have for a planet of its size and distance from the Sun. Can you devise a birth story for the Moon that takes all of these bits of data into account? | text | null |
L_0171 | formation of the moon | T_1198 | Astronomers have carried out computer simulations that are consistent with these facts and have detailed a birth story for the Moon. A little more than 4.5 billion years ago, roughly 70 million years after Earth formed, planetary bodies were being pummeled by asteroids and planetoids of all kinds. Earth was struck by a Mars-sized asteroid (Figure 1.1). An artists depiction of the impact that produced the Moon. The tremendous energy from the impact melted both bodies. The molten material mixed up. The dense metals remained on Earth but some of the molten, rocky material was flung into an orbit around Earth. It eventually accreted into a single body, the Moon. Since both planetary bodies were molten, material could differentiate out of the magma ocean into core, mantle, and crust as they cooled. Earths fast spin is from energy imparted to it by the impact. | text | null |
L_0171 | formation of the moon | T_1199 | Lunar rocks reveal an enormous amount about Earths early days. The Genesis Rock, with a date of 4.5 billion years, is only about 100 million years younger than the solar system (see opening image). The rock is a piece of the Moons anorthosite crust, which was the original crust. Why do you think Moon rocks contain information that is not available from Earths own materials? Can you find how all of the evidence presented in the bullet points above is present in the Moons birth story? | text | null |
L_0172 | formation of the sun and planets | T_1200 | The most widely accepted explanation of how the solar system formed is called the nebular hypothesis. According to this hypothesis, the Sun and the planets of our solar system formed about 4.6 billion years ago from the collapse of a giant cloud of gas and dust, called a nebula. The nebula was drawn together by gravity, which released gravitational potential energy. As small particles of dust and gas smashed together to create larger ones, they released kinetic energy. As the nebula collapsed, the gravity at the center increased and the cloud started to spin because of its angular momentum. As it collapsed further, the spinning got faster, much as an ice skater spins faster when he pulls his arms to his sides during a spin. Much of the clouds mass migrated to its center but the rest of the material flattened out in an enormous disk. The disk contained hydrogen and helium, along with heavier elements and even simple organic molecules. | text | null |
L_0172 | formation of the sun and planets | T_1201 | As gravity pulled matter into the center of the disk, the density and pressure at the center became intense. When the pressure in the center of the disk was high enough, nuclear fusion began. A star was bornthe Sun. The burning star stopped the disk from collapsing further. Meanwhile, the outer parts of the disk were cooling off. Matter condensed from the cloud and small pieces of dust started clumping together. These clumps collided and combined with other clumps. Larger clumps, called An artists painting of a protoplanetary disk. planetesimals, attracted smaller clumps with their gravity. Gravity at the center of the disk attracted heavier particles, such as rock and metal and lighter particles remained further out in the disk. Eventually, the planetesimals formed protoplanets, which grew to become the planets and moons that we find in our solar system today. Because of the gravitational sorting of material, the inner planets Mercury, Venus, Earth, and Mars formed from dense rock and metal. The outer planets Jupiter, Saturn, Uranus and Neptune condensed farther from the Sun from lighter materials such as hydrogen, helium, water, ammonia, and methane. Out by Jupiter and beyond, where its very cold, these materials form solid particles. The nebular hypothesis was designed to explain some of the basic features of the solar system: The orbits of the planets lie in nearly the same plane with the Sun at the center The planets revolve in the same direction The planets mostly rotate in the same direction The axes of rotation of the planets are mostly nearly perpendicular to the orbital plane The oldest moon rocks are 4.5 billion years Click image to the left or use the URL below. URL: | text | null |
L_0173 | fossil fuel formation | T_1202 | Can you name some fossils? How about dinosaur bones or dinosaur footprints? Animal skeletons, teeth, shells, coprolites (otherwise known as feces), or any other remains or traces from a living creature that becomes rock is a fossil. The same processes that formed these fossils also created some of our most important energy resources, fossil fuels. Coal, oil, and natural gas are fossil fuels. Fossil fuels come from living matter starting about 500 million years ago. Millions of years ago, plants used energy from the Sun to form sugars, carbohydrates, and other energy-rich carbon compounds. As plants and animals died, their remains settled on the ground on land and in swamps, lakes, and seas (Figure 1.1). Over time, layer upon layer of these remains accumulated. Eventually, the layers were buried so deeply that they were crushed by an enormous mass of earth. The weight of this earth pressing down on these plant and animal remains created intense heat and pressure. After millions of years of heat and pressure, the material in these layers turned into chemicals called hydrocarbons (Figure 1.2). Hydrocarbons are made of carbon and hydrogen atoms. This molecule with one carbon and four hydrogen atoms is methane. Hydrocarbons can be solid, liquid, or gaseous. The solid form is what we know as coal. The liquid form is petroleum, or crude oil. Natural gas is the gaseous form. The solar energy stored in fossil fuels is a rich source of energy. Although fossil fuels provide very high quality energy, they are non-renewable. Click image to the left or use the URL below. URL: | text | null |
L_0173 | fossil fuel formation | T_1202 | Can you name some fossils? How about dinosaur bones or dinosaur footprints? Animal skeletons, teeth, shells, coprolites (otherwise known as feces), or any other remains or traces from a living creature that becomes rock is a fossil. The same processes that formed these fossils also created some of our most important energy resources, fossil fuels. Coal, oil, and natural gas are fossil fuels. Fossil fuels come from living matter starting about 500 million years ago. Millions of years ago, plants used energy from the Sun to form sugars, carbohydrates, and other energy-rich carbon compounds. As plants and animals died, their remains settled on the ground on land and in swamps, lakes, and seas (Figure 1.1). Over time, layer upon layer of these remains accumulated. Eventually, the layers were buried so deeply that they were crushed by an enormous mass of earth. The weight of this earth pressing down on these plant and animal remains created intense heat and pressure. After millions of years of heat and pressure, the material in these layers turned into chemicals called hydrocarbons (Figure 1.2). Hydrocarbons are made of carbon and hydrogen atoms. This molecule with one carbon and four hydrogen atoms is methane. Hydrocarbons can be solid, liquid, or gaseous. The solid form is what we know as coal. The liquid form is petroleum, or crude oil. Natural gas is the gaseous form. The solar energy stored in fossil fuels is a rich source of energy. Although fossil fuels provide very high quality energy, they are non-renewable. Click image to the left or use the URL below. URL: | text | null |
L_0174 | fossil fuel reserves | T_1203 | Fossil fuels provide about 85% of the worlds energy at this time. Worldwide fossil fuel usage has increased many times over in the past half century (coal - 2.6x, oil - 8x, natural gas - 14x) because of population increases, because of increases in the number of cars, televisions, and other fuel-consuming uses in the developed world, and because of lifestyle improvements in the developing world. The amount of fossil fuels that remain untapped is unknown, but can likely be measured in decades for oil and natural gas and in a few centuries for coal (Figure 1.1). | text | null |
L_0174 | fossil fuel reserves | T_1204 | As the easy-to-reach fossil fuel sources are depleted, alternative sources of fossil fuels are increasingly being exploited (Figure 1.2). These include oil shale and tar sands. Oil shale is rock that contains dispersed oil that has not collected in reservoirs. To extract the oil from the shale requires enormous amounts of hot water. Tar sands are rocky materials mixed with very thick oil. The tar is too thick to pump and so tar sands are strip-mined. Hot water and caustic soda are used to separate the oil from the rock. The environmental consequences of mining these fuels, and of fossil fuel use in general, along with the fact that these fuels do not have a limitless supply, are prompting the development of alternative energy sources in some regions. Click image to the left or use the URL below. URL: A satellite image of an oil-sands mine in Canada. Click image to the left or use the URL below. URL: | text | null |
L_0174 | fossil fuel reserves | T_1204 | As the easy-to-reach fossil fuel sources are depleted, alternative sources of fossil fuels are increasingly being exploited (Figure 1.2). These include oil shale and tar sands. Oil shale is rock that contains dispersed oil that has not collected in reservoirs. To extract the oil from the shale requires enormous amounts of hot water. Tar sands are rocky materials mixed with very thick oil. The tar is too thick to pump and so tar sands are strip-mined. Hot water and caustic soda are used to separate the oil from the rock. The environmental consequences of mining these fuels, and of fossil fuel use in general, along with the fact that these fuels do not have a limitless supply, are prompting the development of alternative energy sources in some regions. Click image to the left or use the URL below. URL: A satellite image of an oil-sands mine in Canada. Click image to the left or use the URL below. URL: | text | null |
L_0175 | fresh water ecosystems | T_1205 | Organisms that live in lakes, ponds, streams, springs or wetlands are part of freshwater ecosystems. These ecosys- tems vary by temperature, pressure (in lakes), the amount of light that penetrates and the type of vegetation that lives there. | text | null |
L_0175 | fresh water ecosystems | T_1206 | Limnology is the study of bodies of fresh water and the organisms that live there. A lake has zones just like the ocean. The ecosystem of a lake is divided into three distinct zones (Figure 1.1): 1. The surface (littoral) zone is the sloped area closest to the edge of the water. 2. The open-water zone (also called the photic or limnetic zone) has abundant sunlight. 3. The deep-water zone (also called the aphotic or profundal zone) has little or no sunlight. There are several life zones found within a lake: In the littoral zone, sunlight promotes plant growth, which provides food and shelter to animals such as snails, insects, and fish. In the open-water zone, other plants and fish, such as bass and trout, live. The deep-water zone does not have photosynthesis since there is no sunlight. Most deep-water organisms are scavengers, such as crabs and catfish that feed on dead organisms that fall to the bottom of the lake. Fungi and bacteria aid in the decomposition in the deep zone. Though different creatures live in the oceans, ocean waters also have these same divisions based on sunlight with similar types of creatures that live in each of the zones. The three primary zones of a lake are the littoral, open-water, and deep-water zones. | text | null |
L_0175 | fresh water ecosystems | T_1207 | Wetlands are lands that are wet for significant periods of time. They are common where water and land meet. Wetlands can be large flat areas or relatively small and steep areas. Wetlands are rich and unique ecosystems with many species that rely on both the land and the water for survival. Only specialized plants are able to grow in these conditions. Wetlands tend have a great deal of biological diversity. Wetland ecosystems can also be fragile systems that are sensitive to the amount and quality of water present within them. Click image to the left or use the URL below. URL: | text | null |
L_0175 | fresh water ecosystems | T_1208 | Marshes are shallow wetlands around lakes, streams, or the ocean where grasses and reeds are common, but trees are not (Figure 1.2). Frogs, turtles, muskrats, and many varieties of birds are at home in marshes. A salt marsh on Cape Cod in Mas- sachusetts. | text | null |
L_0175 | fresh water ecosystems | T_1209 | A swamp is a wetland with lush trees and vines found in low-lying areas beside slow-moving rivers (Figure 1.3). Like marshes, they are frequently or always inundated with water. Since the water in a swamp moves slowly, oxygen in the water is often scarce. Swamp plants and animals must be adapted for these low-oxygen conditions. Like marshes, swamps can be fresh water, salt water, or a mixture of both. | text | null |
L_0175 | fresh water ecosystems | T_1210 | As mentioned above, wetlands are home to many different species of organisms. Although they make up only 5% of the area of the United States, wetlands contain more than 30% of the plant types. Many endangered species live in wetlands, so wetlands are protected from human use. Wetlands also play a key biological role by removing pollutants from water. For example, they can trap and use fertilizer that has washed off a farmers field, and therefore they prevent that fertilizer from contaminating another body of water. Since wetlands naturally purify water, preserving wetlands also helps to maintain clean supplies of water. | text | null |
L_0176 | galaxies | T_1211 | Galaxies are the biggest groups of stars and can contain anywhere from a few million stars to many billions of stars. Every star that is visible in the night sky is part of the Milky Way Galaxy. To the naked eye, the closest major galaxy the Andromeda Galaxy, shown in Figure 1.1 looks like only a dim, fuzzy spot. But that fuzzy spot contains one trillion 1,000,000,000,000 stars! Galaxies are divided into three types according to shape: spiral galaxies, elliptical galaxies, and irregular galaxies. | text | null |
L_0176 | galaxies | T_1212 | Spiral galaxies spin, so they appear as a rotating disk of stars and dust, with a bulge in the middle, like the Sombrero Galaxy shown in Figure 1.2. Several arms spiral outward in the Pinwheel Galaxy (seen in Figure 1.2) and are appropriately called spiral arms. Spiral galaxies have lots of gas and dust and lots of young stars. The Andromeda Galaxy is a large spiral galaxy similar to the Milky Way. (a) The Sombrero Galaxy is a spiral galaxy that we see from the side so the disk and central bulge are visible. (b) The Pinwheel Galaxy is a spiral galaxy that we see face-on so we can see the spiral arms. Because they contain lots of young stars, spiral arms tend to be blue. | text | null |
L_0176 | galaxies | T_1212 | Spiral galaxies spin, so they appear as a rotating disk of stars and dust, with a bulge in the middle, like the Sombrero Galaxy shown in Figure 1.2. Several arms spiral outward in the Pinwheel Galaxy (seen in Figure 1.2) and are appropriately called spiral arms. Spiral galaxies have lots of gas and dust and lots of young stars. The Andromeda Galaxy is a large spiral galaxy similar to the Milky Way. (a) The Sombrero Galaxy is a spiral galaxy that we see from the side so the disk and central bulge are visible. (b) The Pinwheel Galaxy is a spiral galaxy that we see face-on so we can see the spiral arms. Because they contain lots of young stars, spiral arms tend to be blue. | text | null |
L_0176 | galaxies | T_1213 | Figure 1.3 shows a typical egg-shaped elliptical galaxy. The smallest elliptical galaxies are as small as some globular clusters. Giant elliptical galaxies, on the other hand, can contain over a trillion stars. Elliptical galaxies are reddish to yellowish in color because they contain mostly old stars. Most elliptical galaxies contain very little gas and dust because the gas and dust have already formed into stars. However, some elliptical galaxies, such as the one shown in Figure 1.4, contain lots of dust. Why might some elliptical galaxies contain dust? | text | null |
L_0176 | galaxies | T_1213 | Figure 1.3 shows a typical egg-shaped elliptical galaxy. The smallest elliptical galaxies are as small as some globular clusters. Giant elliptical galaxies, on the other hand, can contain over a trillion stars. Elliptical galaxies are reddish to yellowish in color because they contain mostly old stars. Most elliptical galaxies contain very little gas and dust because the gas and dust have already formed into stars. However, some elliptical galaxies, such as the one shown in Figure 1.4, contain lots of dust. Why might some elliptical galaxies contain dust? | text | null |
L_0176 | galaxies | T_1214 | Is the galaxy in Figure 1.5 a spiral galaxy or an elliptical galaxy? It is neither one! Galaxies that are not clearly elliptical galaxies or spiral galaxies are irregular galaxies. How might an irregular galaxy form? Most irregular galaxies were once spiral or elliptical galaxies that were then deformed either by gravitational attraction to a larger galaxy or by a collision with another galaxy. This galaxy, called NGC 1427A, has nei- ther a spiral nor an elliptical shape. | text | null |
L_0176 | galaxies | T_1215 | Dwarf galaxies are small galaxies containing only a few million to a few billion stars. Dwarf galaxies are the most common type in the universe. However, because they are relatively small and dim, we dont see as many dwarf galaxies from Earth. Most dwarf galaxies are irregular in shape. However, there are also dwarf elliptical galaxies and dwarf spiral galaxies. Look back at the picture of the elliptical galaxy. In the figure, you can see two dwarf elliptical galaxies that are companions to the Andromeda Galaxy. One is a bright sphere to the left of center, and the other is a long ellipse below and to the right of center. Dwarf galaxies are often found near larger galaxies. They sometimes collide with and merge into their larger neighbors. 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_0177 | geologic time scale | T_1216 | To be able to discuss Earth history, scientists needed some way to refer to the time periods in which events happened and organisms lived. With the information they collected from fossil evidence and using Stenos principles, they created a listing of rock layers from oldest to youngest. Then they divided Earths history into blocks of time with each block separated by important events, such as the disappearance of a species of fossil from the rock record. Since many of the scientists who first assigned names to times in Earths history were from Europe, they named the blocks of time from towns or other local places where the rock layers that represented that time were found. From these blocks of time the scientists created the geologic time scale (Figure 1.1). In the geologic time scale the youngest ages are on the top and the oldest on the bottom. Why do you think that the more recent time periods are divided more finely? Do you think the divisions in the scale below are proportional to the amount of time each time period represented in Earth history? In what eon, era, period and epoch do we now live? We live in the Holocene (sometimes called Recent) epoch, Quaternary period, Cenozoic era, and Phanerozoic eon. | text | null |
L_0177 | geologic time scale | T_1217 | Its always fun to think about geologic time in a framework that we can more readily understand. Here are when some major events in Earth history would have occurred if all of earth history was condensed down to one calendar year. January 1 12 am: Earth forms from the planetary nebula - 4600 million years ago February 25, 12:30 pm: The origin of life; the first cells - 3900 million years ago March 4, 3:39 pm: Oldest dated rocks - 3800 million years ago March 20, 1:33 pm: First stromatolite fossils - 3600 million years ago July 17, 9:54 pm: first fossil evidence of cells with nuclei - 2100 million years ago November 18, 5:11 pm: Cambrian Explosion - 544 million years ago December 1, 8:49 am: first insects - 385 million years ago December 2, 3:54 am: first land animals, amphibians - 375 million years ago December 5, 5:50 pm: first reptiles - 330 million years ago December 12, 12:09 pm: Permo-Triassic Extinction - 245 million years ago December 13, 8:37 pm: first dinosaurs - 228 million years ago December 14, 9:59 am: first mammals 220 million years ago December 22, 8:24 pm: first flowering plants - 115 million years ago December 26, 7:52 pm: Cretaceous-Tertiary Extinction - 66 million years ago December 26, 9:47 pm: first ancestors of dogs - 64 million years ago December 27, 5:25 am: widespread grasses - 60 million years ago December 27, 11:09 am: first ancestors of pigs and deer - 57 million years ago December 28, 9:31 pm: first monkeys - 39 million years ago December 31, 5:18 pm: oldest hominid - 4 million years ago December 31, 11:02 pm: oldest direct human ancestor - 1 million years ago December 31, 11:48 pm: first modern human - 200,000 years ago December 31, 11:59 pm: Revolutionary War - 235 years ago | text | null |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.