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L_0088 | soils | T_0895 | Pedocal soil forms where grasses and brush are common (Figure 9.11). The climate is drier, with less than 65 cm of rain per year. With less rain, there is less chemical weathering. There is less organic material and the soils are slightly less fertile. | text | null |
L_0088 | soils | T_0896 | A third important type of soil is laterite. Laterite forms in tropical areas. Temperatures are warm and rain falls every day (Figure 9.12). So much rain falls that chemical weathering is intense. All soluble minerals are washed from the soil. Plant nutrients get leached or carried away. There is practically no humus. Laterite soils are often red in color from the iron oxides. If laterites are exposed to the Sun, they bake as hard as a brick. | text | null |
L_0088 | soils | T_0897 | Soil is a renewable resource. But it is only renewable if we take care of it. Natural events can degrade soil. These events include droughts, floods, insect plagues, or diseases that damage soil ecosystems. Human activities can also degrade soil. There are many ways in which people neglect or abuse this important resource. | text | null |
L_0088 | soils | T_0898 | People remove a lot of vegetation. They log forests or prepare the land for farming or construction. Even just walking or riding your bike over the same place can kill the grass. But plants help to hold the soil in place (Figure faster than it is forming. In these locations, soil is a non-renewable resource. Soils may also remain in place but become degraded. Soil is contaminated if too much salt accumulates. Soil can also be contaminated by pollutants. | text | null |
L_0088 | soils | T_0899 | There are many ways to protect soil. We can add organic material like manure or compost. This increases the soils fertility. Increased fertility improves the soils ability to hold water and nutrients. Inorganic fertilizers also increase fertility. These fertilizers are less expensive than natural fertilizers, but they do not provide the same long term benefits. Careful farming helps to keep up soil quality each season. One way is to plant different crops each year. Another is to alternate the crops planted in each row of the field. These techniques preserve and replenish soil nutrients. Planting nutrient rich cover crops helps the soil. Planting trees as windbreaks, plowing along contours of a field, or building terraces into steeper slopes all help to hold soil in place (Figure 9.14). No-till or low-till farming disturbs the ground as little as possible during planting. | text | null |
L_0097 | avoiding soil loss | T_0935 | Bad farming practices and a return to normal rainfall levels after an unusually wet period led to the Dust Bowl. In some regions more than 75% of the topsoil blew away. This is the most extreme example of soil erosion the United States has ever seen. Still, in many areas of the world, the rate of soil erosion is many times greater than the rate at which it is forming. Drought, insect plagues, or outbreaks of disease are natural cycles of events that can negatively impact ecosystems and the soil, but there are also many ways in which humans neglect or abuse this important resource. Soils can also be contaminated if too much salt accumulates in the soil or where pollutants sink into the ground. One harmful practice is removing the vegetation that helps to hold soil in place. Sometimes just walking or riding your bike over the same place will kill the grass that normally grows there. Land is also deliberately cleared or deforested for wood. The loose soils then may be carried away by wind or running water. A farmer and his sons walk through a dust storm in Cimarron County, Oklahoma in 1936. Click image to the left or use the URL below. URL: | text | null |
L_0097 | avoiding soil loss | T_0936 | Soil is only a renewable resource if it is carefully managed. There are many practices that can protect and preserve soil resources. | text | null |
L_0097 | avoiding soil loss | T_0937 | Adding organic material to the soil in the form of plant or animal waste, such as compost or manure, increases the fertility of the soil and improves its ability to hold on to water and nutrients (Figure 1.2). Inorganic fertilizer can also temporarily increase the fertility of a soil and may be less expensive or time consuming, but it does not provide the same long-term improvements as organic materials. | text | null |
L_0097 | avoiding soil loss | T_0938 | Soil is a natural resource that is vitally important for sustaining natural habitats and for growing food. Although soil is a renewable resource, it is renewed slowly, taking hundreds or thousands of years for a good fertile soil to develop. Organic material can be added to soil to help increase its fertility. Most of the best land for farming is already being cultivated. With human populations continuing to grow, it is extremely important to protect our soil resources. Agricultural practices such as rotating crops, alternating the types of crops planted in each row, and planting nutrient-rich cover crops all help to keep soil more fertile as it is used season after season. Planting trees as windbreaks, plowing along contours of the field, or building terraces into steeper slopes will all help to hold soil in place (Figure 1.3). No-till or low-tillage farming helps to keep soil in place by disturbing the ground as little as possible when planting. Steep slopes can be terraced to make level planting areas and decrease surface water runoff and erosion. The rate of topsoil loss in the United States and other developed countries has decreased recently as better farming practices have been adopted. Unfortunately, in developing nations, soil is often not protected. Table 1.1 shows some steps that we can take to prevent erosion. Some are things that can be done by farmers or developers. Others are things that individual homeowners or community members can implement locally. Source of Erosion Strategies for Prevention Leave leaf litter on the ground in the winter. Grow cover crops, special crops grown in the winter to cover the soil. Plant tall trees around fields to buffer the effects of wind. Drive tractors as little as possible. Use drip irrigation that puts small amounts of water in the ground frequently. Avoid watering crops with sprinklers that make big water drops on the ground. Keep fields as flat as possible to avoid soil erod- ing down hill. Grazing Animals Move animals throughout the year, so they dont consume all the vegetation in one spot. Keep animals away from stream banks, where hills are especially prone to erosion. Logging and Mining Reduce the amount of land that is logged and mined. Reduce the number of roads that are built to access logging areas. Avoid logging and mining on steep lands. Cut only small areas at one time and quickly replant logged areas with new seedlings. Development Reduce the amount of land area that is developed into urban areas, parking lots, etc. Keep as much green space in cities as possible, such as parks or strips where plants can grow. Invest in and use new technologies for parking lots that make them permeable to water in order to reduce runoff of water. Recreational Activities Avoid using off-road vehicles on hilly lands. Stay on designated trails. Avoid building on steep hills. Grade surrounding land to distribute water rather than collecting it in one place. Where water collects, drain to creeks and rivers. Landscape with plants that minimize erosion. Click image to the left or use the URL below. URL: | text | null |
L_0097 | avoiding soil loss | T_0938 | Soil is a natural resource that is vitally important for sustaining natural habitats and for growing food. Although soil is a renewable resource, it is renewed slowly, taking hundreds or thousands of years for a good fertile soil to develop. Organic material can be added to soil to help increase its fertility. Most of the best land for farming is already being cultivated. With human populations continuing to grow, it is extremely important to protect our soil resources. Agricultural practices such as rotating crops, alternating the types of crops planted in each row, and planting nutrient-rich cover crops all help to keep soil more fertile as it is used season after season. Planting trees as windbreaks, plowing along contours of the field, or building terraces into steeper slopes will all help to hold soil in place (Figure 1.3). No-till or low-tillage farming helps to keep soil in place by disturbing the ground as little as possible when planting. Steep slopes can be terraced to make level planting areas and decrease surface water runoff and erosion. The rate of topsoil loss in the United States and other developed countries has decreased recently as better farming practices have been adopted. Unfortunately, in developing nations, soil is often not protected. Table 1.1 shows some steps that we can take to prevent erosion. Some are things that can be done by farmers or developers. Others are things that individual homeowners or community members can implement locally. Source of Erosion Strategies for Prevention Leave leaf litter on the ground in the winter. Grow cover crops, special crops grown in the winter to cover the soil. Plant tall trees around fields to buffer the effects of wind. Drive tractors as little as possible. Use drip irrigation that puts small amounts of water in the ground frequently. Avoid watering crops with sprinklers that make big water drops on the ground. Keep fields as flat as possible to avoid soil erod- ing down hill. Grazing Animals Move animals throughout the year, so they dont consume all the vegetation in one spot. Keep animals away from stream banks, where hills are especially prone to erosion. Logging and Mining Reduce the amount of land that is logged and mined. Reduce the number of roads that are built to access logging areas. Avoid logging and mining on steep lands. Cut only small areas at one time and quickly replant logged areas with new seedlings. Development Reduce the amount of land area that is developed into urban areas, parking lots, etc. Keep as much green space in cities as possible, such as parks or strips where plants can grow. Invest in and use new technologies for parking lots that make them permeable to water in order to reduce runoff of water. Recreational Activities Avoid using off-road vehicles on hilly lands. Stay on designated trails. Avoid building on steep hills. Grade surrounding land to distribute water rather than collecting it in one place. Where water collects, drain to creeks and rivers. Landscape with plants that minimize erosion. Click image to the left or use the URL below. URL: | text | null |
L_0105 | cenozoic plate tectonics | T_0971 | The Cenozoic began around 65.5 million years ago and continues today. Although it accounts for only about 1.5% of the Earths total history, as the most recent era it is the one scientists know the most about. Much of what has been discussed elsewhere in CK-12 Earth Science Concepts For High School describes the geological situation of the Cenozoic. A few highlights are mentioned here. | text | null |
L_0105 | cenozoic plate tectonics | T_0972 | The paleogeography of the era was very much like it is today. Early in the Cenozoic, blocks of crust uplifted to form the Rocky Mountains, which were later eroded away and then uplifted again. Subduction off of the Pacific Northwest formed the Cascades volcanic arc. The Basin and Range province that centers on Nevada is where crust is being pulled apart. | text | null |
L_0105 | cenozoic plate tectonics | T_0973 | The San Andreas Fault has grown where the Pacific and North American plates meet. The plate tectonic evolution of that plate boundary is complex and interesting (Figure 1.1). The Farallon Plate was subducting beneath the North American Plate 30 Ma. By 20 Ma the Pacific Plate and East Pacific Rise spreading center had started to subduct, splitting the Farallon Plate into two smaller plates. Transform motion where the Pacific and North American plates meet formed the San Andreas Fault. The fault moved inland and at present small sea floor spreading basins along with the transform motion of the San Andreas are splitting Baja California from mainland Mexico. This figure shows the evolution of the San Andreas Fault zone from 30 million years ago (bottom) to present (top). Although most plate tectonic activity involves continents moving apart, smaller regions are coming together. Africa collided with Eurasia to create the Alps. India crashed into Asia to form the Himalayas. 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_0105 | cenozoic plate tectonics | T_0974 | As the continents moved apart, climate began to cool. When Australia and Antarctica separated, the Antarctic Circumpolar Current could then move the frigid water around Antarctica and spread it more widely around the planet. Antarctica drifted over the south polar region and the continent began to grow a permanent ice cap in the Oligocene. The climate warmed in the early Miocene but then began to cool again in the late Miocene and Pliocene when glaciers began to form. During the Pleistocene ice ages, which began 2.6 million years ago, glaciers advanced and retreated four times (Figure 1.2). During the retreats, the climate was often warmer than it is today. Glacial ice at its maximum during the Pleistocene. These continental ice sheets were extremely thick, like the Antarctic ice cap is today. The Pleistocene ice ages guided the evolution of life in the Cenozoic, including the evolution of humans. | text | null |
L_0108 | chemical weathering | T_0981 | Chemical weathering is the other important type of weathering. Chemical weathering may change the size of pieces of rock materials, but definitely changes the composition. So one type of mineral changes into a different mineral. Chemical weathering works through chemical reactions that cause changes in the minerals. | text | null |
L_0108 | chemical weathering | T_0982 | Most minerals form at high pressure or high temperatures deep in the crust, or sometimes in the mantle. When these rocks are uplifed onto Earths surface, they are at very low temperatures and pressures. This is a very different environment from the one in which they formed and the minerals are no longer stable. In chemical weathering, minerals that were stable inside the crust must change to minerals that are stable at Earths surface. | text | null |
L_0108 | chemical weathering | T_0983 | Remember that the most common minerals in Earths crust are the silicate minerals. Many silicate minerals form in igneous or metamorphic rocks. The minerals that form at the highest temperatures and pressures are the least stable at the surface. Clay is stable at the surface and chemical weathering converts many minerals to clay (Figure 1.1). There are many types of chemical weathering because there are many agents of chemical weathering. Deforestation in Brazil reveals the under- lying clay-rich soil. | text | null |
L_0108 | chemical weathering | T_0984 | A water molecule has a very simple chemical formula, H2 O, two hydrogen atoms bonded to one oxygen atom. But water is pretty remarkable in terms of all the things it can do. Remember that water is a polar molecule. The positive side of the molecule attracts negative ions and the negative side attracts positive ions. So water molecules separate the ions from their compounds and surround them. Water can completely dissolve some minerals, such as salt. Weathered rock in Walnut Canyon near Flagstaff, Arizona. Hydrolysis is the name of the chemical reaction between a chemical compound and water. When this reaction takes place, water dissolves ions from the mineral and carries them away. These elements have been leached. Through hydrolysis, a mineral such as potassium feldspar is leached of potassium and changed into a clay mineral. Clay minerals are more stable at the Earths surface. | text | null |
L_0108 | chemical weathering | T_0985 | Carbon dioxide (CO2 ) combines with water as raindrops fall through the atmosphere. This makes a weak acid, called carbonic acid. Carbonic acid is a very common in nature, where it works to dissolve rock. Pollutants, such as sulfur and nitrogen from fossil fuel burning, create sulfuric and nitric acid. Sulfuric and nitric acids are the two main components of acid rain, which accelerates chemical weathering (Figure 1.3). Acid rain is discussed in the chapter Human Impacts on Earths Systems. This statue at Washington Square Arch in New York City exhibits damage from acid rain. | text | null |
L_0108 | chemical weathering | T_0986 | Oxidation is a chemical reaction that takes place when oxygen reacts with another element. Oxygen is very strongly chemically reactive. The most familiar type of oxidation is when iron reacts with oxygen to create rust (Figure 1.4). Minerals that are rich in iron break down as the iron oxidizes and forms new compounds. Iron oxide produces the red color in soils. | text | null |
L_0108 | chemical weathering | T_0987 | Now that you know what chemical weathering is, can you think of some other ways chemical weathering might occur? Chemical weathering can also be contributed to by plants and animals. As plant roots take in soluble ions as nutrients, certain elements are exchanged. Plant roots and bacterial decay use carbon dioxide in the process of respiration. | text | null |
L_0108 | chemical weathering | T_0988 | Mechanical weathering increases the rate of chemical weathering. As rock breaks into smaller pieces, the surface area of the pieces increases Figure 1.5. With more surfaces exposed, there are more surfaces on which chemical weathering can occur. Mechanical weathering may increase the rate of chemical weathering. Click image to the left or use the URL below. URL: | text | null |
L_0112 | clouds | T_1006 | Humidity is the amount of water vapor in the air in a particular spot. We usually use the term to mean relative humidity, the percentage of water vapor a certain volume of air is holding relative to the maximum amount it can contain. If the humidity today is 80%, it means that the air contains 80% of the total amount of water it can hold at that temperature. What will happen if the humidity increases to more than 100%? The excess water condenses and forms precipitation. Since warm air can hold more water vapor than cool air, raising or lowering temperature can change airs relative humidity (Figure 1.1). The temperature at which air becomes saturated with water is called the airs dew point. This term makes sense, because water condenses from the air as dew if the air cools down overnight and reaches 100% humidity. This diagram shows the amount of water air can hold at different temperatures. The temperatures are given in degrees Cel- sius. | text | null |
L_0112 | clouds | T_1007 | Water vapor is not visible unless it condenses to become a cloud. Water vapor condenses around a nucleus, such as dust, smoke, or a salt crystal. This forms a tiny liquid droplet. Billions of these water droplets together make a cloud. | text | null |
L_0112 | clouds | T_1008 | Clouds form when air reaches its dew point. This can happen in two ways: (1) Air temperature stays the same but humidity increases. This is common in locations that are warm and humid. (2) Humidity remains the same, but temperature decreases. When the air cools enough to reach 100% humidity, water droplets form. Air cools when it comes into contact with a cold surface or when it rises. Rising air creates clouds when it has been warmed at or near the ground level and then is pushed up over a mountain or mountain range or is thrust over a mass of cold, dense air. Click image to the left or use the URL below. URL: | text | null |
L_0112 | clouds | T_1009 | Clouds have a big influence on weather: by preventing solar radiation from reaching the ground. by absorbing warmth that is re-emitted from the ground. as the source of precipitation. When there are no clouds, there is less insulation. As a result, cloudless days can be extremely hot, and cloudless nights can be very cold. For this reason, cloudy days tend to have a lower range of temperatures than clear days. | text | null |
L_0112 | clouds | T_1010 | Clouds are classified in several ways. The most common classification used today divides clouds into four separate cloud groups, which are determined by their altitude (Figure 1.2). The four cloud types and where they are found in the atmosphere. High clouds form from ice crystals where the air is extremely cold and can hold little water vapor. Cirrus, cirrostratus, and cirrocumulus are all names of high clouds. Middle clouds, including altocumulus and altostratus clouds, may be made of water droplets, ice crystals or both, depending on the air temperatures. Thick and broad altostratus clouds are gray or blue-gray. They often cover the entire sky and usually mean a large storm, bearing a lot of precipitation, is coming. Low clouds are nearly all water droplets. Stratus, stratocumulus, and nimbostratus clouds are common low clouds. Nimbostratus clouds are thick and dark. They bring steady rain or snow. Vertical clouds, clouds with the prefix "cumulo-," grow vertically instead of horizontally and have their bases at low altitude and their tops at high or middle altitude. Clouds grow vertically when strong air currents are rising upward. Precipitating clouds are nimbus clouds. | text | null |
L_0112 | clouds | T_1011 | Fog (Figure 1.3) is a cloud located at or near the ground . When humid air near the ground cools below its dew point, fog is formed. Each type of fog forms in a different way. Radiation fog forms at night when skies are clear and the relative humidity is high. As the ground cools, the bottom layer of air cools below its dew point. Tule fog is an extreme form of radiation fog found in some regions. San Francisco, California, is famous for its summertime advection fog. Warm, moist Pacific Ocean air blows over the cold California current and cools below its dew point. Sea breezes bring the fog onshore. Steam fog appears in autumn when cool air moves over a warm lake. Water evaporates from the lake surface and condenses as it cools, appearing like steam. Warm humid air travels up a hillside and cools below its dew point to create upslope fog. (a) Tule fog in the Central Valley of California. (b) Advection fog in San Francisco. (c) Steam fog over a lake. (d) Upslope fog in Terespolis city, Rio de Janeiro State, Brazil. Fog levels are declining along the California coast as climate warms. The change in fog may have big ecological changes for the state. Click image to the left or use the URL below. URL: | text | null |
L_0117 | composition of the atmosphere | T_1027 | Several properties of the atmosphere change with altitude, but the composition of the natural gases does not. The proportions of gases in the atmosphere are everywhere the same, with one exception. At about 20 km to 40 km above the surface, there is a greater concentration of ozone molecules than in other portions of the atmosphere. This is called the ozone layer. | text | null |
L_0117 | composition of the atmosphere | T_1028 | Nitrogen and oxygen together make up 99% of the planets atmosphere. Nitrogen makes up the bulk of the atmosphere, but is not involved in geological or biological processes in its gaseous form. Nitrogen fixing is described in the chapter Life on Earth. Oxygen is extremely important because it is needed by animals for respiration. The rest of the gases are minor components but sometimes are very important (Figure 1.1). Nitrogen and oxygen make up 99% of the atmosphere; carbon dioxide is a very important minor component. | text | null |
L_0117 | composition of the atmosphere | T_1029 | Humidity is the amount of water vapor in the air. Humidity varies from place to place and season to season. This fact is obvious if you compare a summer day in Atlanta, Georgia, where humidity is high, with a winter day in Phoenix, Arizona, where humidity is low. When the air is very humid, it feels heavy or sticky. Dry air usually feels more comfortable. When humidity is high, water vapor makes up only about 4% of the atmosphere. Where around the globe is mean atmospheric water vapor higher and where is it lower (Figure 1.2)? Why? Higher humidity is found around the equatorial regions because air temperatures are higher and warm air can hold more moisture than cooler air. Of course, humidity is lower near the polar regions because air temperature is lower. | text | null |
L_0117 | composition of the atmosphere | T_1030 | Remember that greenhouse gases trap heat in the atmosphere. Important natural greenhouse gases include carbon dioxide, methane, water vapor, and ozone. CFCs and some other man-made compounds are also greenhouse gases. | text | null |
L_0117 | composition of the atmosphere | T_1031 | Some of what is in the atmosphere is not gas. Particles of dust, soil, fecal matter, metals, salt, smoke, ash, and other solids make up a small percentage of the atmosphere and are called particulates. Particles provide starting points (or nuclei) for water vapor to condense on and form raindrops. Some particles are pollutants. Click image to the left or use the URL below. URL: | text | null |
L_0122 | dark matter | T_1041 | The things we observe in space are objects that emit some type of electromagnetic radiation. However, scientists think that matter that emits light makes up only a small part of the matter in the universe. The rest of the matter, about 80%, is dark matter. Dark matter emits no electromagnetic radiation, so we cant observe it directly. However, astronomers know that dark matter exists because its gravity affects the motion of objects around it. When astronomers measure how spiral galaxies rotate, they find that the outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than they can see. Gravitational lensing occurs when light is bent from a very distant bright source around a super-massive object (Figure 1.1). To explain strong gravitational lensing, more matter than is observed must be present. With so little to go on, astronomers dont really know much about the nature of dark matter. One possibility is that it could just be ordinary matter that does not emit radiation in objects such as black holes, neutron stars, and brown dwarfs objects larger than Jupiter but smaller than the smallest stars. But astronomers cannot find enough of these types of objects, which they have named MACHOs (massive astrophyiscal compact halo object), to account for all the dark matter, so they are thought to be only a small part of the total. Another possibility is that the dark matter is very different from the ordinary matter we see. Some appear to be particles that have gravity, but dont otherwise appear to interact with other particles. Scientists call these theoretical particles WIMPs, which stands for Weakly Interactive Massive Particles. Most scientists who study dark matter think that the dark matter in the universe is a combination of MACHOs and some type of exotic matter, such as WIMPs. Researching dark matter is an active area of scientific research, and astronomers knowledge about dark matter is changing rapidly. | text | null |
L_0122 | dark matter | T_1042 | Astronomers who study the expansion of the universe are interested in knowing the rate of that expansion. Is the rate fast enough to overcome the attractive pull of gravity? If yes, then the universe will expand forever, although the expansion will slow down over time. If no, then the universe would someday start to contract, and eventually get squeezed together in a big crunch, the opposite of the Big Bang. Recently, astronomers have made a discovery that answers that question: the rate at which the universe is expanding is actually increasing. In other words, the universe is expanding faster now than ever before, and in the future it will expand even faster. So now astronomers think that the universe will keep expanding forever. But it also proposes a perplexing new question: what is causing the expansion of the universe to accelerate? One possible hypothesis involves a new, hypothetical form of energy called dark energy (Figure 1.2). Some scientists think that dark energy makes up as much as 71% of the total energy content of the universe. Today matter makes up a small percentage of the universe, but at the start of the universe it made up much more. Where did dark energy, if it even exists, come from? Other scientists have other hypotheses about why the universe is continuing to expand; the causes of the universes expansion is another unanswered question that scientists are researching. Click image to the left or use the URL below. URL: | text | null |
L_0122 | dark matter | T_1043 | Meet one of the three winners of the 2011 Nobel Prize in Physics, Lawrence Berkeley Lab astrophysicist Saul Perlmutter. He explains how dark energy, which makes up 70 percent of the universe, is causing our universe to expand. Click image to the left or use the URL below. URL: | text | null |
L_0129 | divergent plate boundaries | T_1057 | Were on a new trip now. We will start in Mexico, in the region surrounding the Gulf of California, where a divergent plate boundary is rifting Baja California and mainland Mexico apart. Then we will move up into California, where plates on both sides of a transform boundary are sliding past each other. Finally well end up off of the Pacific Northwest, where a divergent plate boundary is very near a subduction zone just offshore. In the Figure 1.1 a red bar where seafloor spreading is taking place. A long black line is a transform fault and a black line with hatch marks is a trench where subduction is taking place. Notice how one type of plate boundary transitions into another. | text | null |
L_0129 | divergent plate boundaries | T_1058 | A divergent plate boundary on land rips apart continents (Figure 1.2). In continental rifting, magma rises beneath the continent, causing it to become thinner, break, and ultimately split apart. New ocean crust erupts in the void, ultimately creating an ocean between continents. On either side of the ocean are now two different lithospheric plates. This is how continents split apart. These features are well displayed in the East African Rift, where rifting has begun, and in the Red Sea, where water is filling up the basin created by seafloor spreading. The Atlantic Ocean is the final stage, where rifting is now separating two plates of oceanic crust. | text | null |
L_0129 | divergent plate boundaries | T_1059 | Baja California is a state in Mexico just south of California. In the Figure 1.3, Baja California is the long, skinny land mass on the left. You can see that the Pacific Ocean is growing in between Baja California and mainland Mexico. This body of water is called the Gulf of California or, more romantically, the Sea of Cortez. Baja is on the Pacific Plate and the rest of Mexico is on the North American Plate. Extension is causing the two plates to move apart and will eventually break Baja and the westernmost part of California off of North America. The Gulf of California will expand into a larger sea. Rifting has caused volcanic activity on the Baja California peninsula as seen in the Figure 1.4. Can you relate what is happening at this plate boundary to what happened when Pangaea broke apart? | text | null |
L_0130 | divergent plate boundaries in the oceans | T_1060 | Iceland provides us with a fabulous view of a mid-ocean ridge above sea level (Figure 1.1) As you can see, where plates diverge at a mid-ocean ridge is a rift valley that marks the boundary between the two plates. Basalt lava erupts into that rift valley and forms new seafloor. Seafloor on one side of the rift is part of one plate and seafloor on the other side is part of another plate. Leif the Lucky Bridge straddles the divergent plate boundary. Look back at the photo at the top. You may think that the rock on the left side of the valley looks pretty much like the rock on the right side. Thats true - its all basalt and it even all has the same magnetic polarity. The rocks on both sides are extremely young. Whats different is that the rock one side of the bridge is the youngest rock of the North American Plate while the rock on the other side is the youngest rock on the Eurasian plate. This is a block diagram of a divergent plate boundary. Remember that most of these are on the seafloor and only in Iceland do we get such a good view of a divergent plate boundary in the ocean. | text | null |
L_0130 | divergent plate boundaries in the oceans | T_1061 | Remember that the mid-ocean ridge is where hot mantle material upwells in a convection cell. The upwelling mantle melts due to pressure release to form lava. Lava flows at the surface cool rapidly to become basalt, but deeper in the crust, magma cools more slowly to form gabbro. The entire ridge system is made up of igneous rock that is either extrusive or intrusive. The seafloor is also igneous rock with some sediment that has fallen onto it. Earthquakes are common at mid-ocean ridges since the movement of magma and oceanic crust results in crustal shaking. Click image to the left or use the URL below. URL: | text | null |
L_0134 | earthquake characteristics | T_1080 | An earthquake is sudden ground movement caused by the sudden release of energy stored in rocks. Earthquakes happen when so much stress builds up in the rocks that the rocks rupture. The energy is transmitted by seismic waves. Earthquakes can be so small they go completely unnoticed, or so large that it can take years for a region to recover. | text | null |
L_0134 | earthquake characteristics | T_1081 | The description of how earthquakes occur is called elastic rebound theory (Figure 1.1). Elastic rebound theory. Stresses build on both sides of a fault, causing the rocks to deform plastically (Time 2). When the stresses become too great, the rocks break and end up in a different location (Time 3). This releases the built up energy and creates an earthquake. Click image to the left or use the URL below. URL: | text | null |
L_0134 | earthquake characteristics | T_1082 | In an earthquake, the initial point where the rocks rupture in the crust is called the focus. The epicenter is the point on the land surface that is directly above the focus (Figure 1.2). In the vertical cross section of crust, there are two features labeled - the focus and the epicenter, which is directly above the focus. Click image to the left or use the URL below. URL: | text | null |
L_0135 | earthquake damage | T_1083 | We know that earthquakes kill lots of people. However, the ground shaking almost never kills people, and the ground does not swallow someone up. Fatalities depend somewhat on an earthquakes size and the type of ground people inhabit. But much of what determines the number of fatalities depends on the quality of structures. People are killed when structures fall on them. More damage is done and more people are killed by the fires that follow an earthquake than the earthquake itself. | text | null |
L_0135 | earthquake damage | T_1084 | Population density. The magnitude 9.2 Great Alaska Earthquake, near Anchorage, of 1964 resulted in only 131 deaths. At the time few people lived in the area (Figure 1.1). Not size. Only about 2,000 people died in the 1960 Great Chilean earthquake, the largest earthquake ever recorded. The Indian Ocean earthquake of 2004 was one of the largest ever, but most of the 230,000 fatalities were caused by the tsunami, not the earthquake itself. Ground type. Solid bedrock vibrates less than soft sediments, so there is less damage on bedrock. Sediments that are saturated with water undergo liquefaction and become like quicksand (Figure 1.2). Soil on a hillside may become a landslide. Liquefaction of sediments in Mexico City caused the collapse of many buildings in the 1985 earthquake. | text | null |
L_0135 | earthquake damage | T_1084 | Population density. The magnitude 9.2 Great Alaska Earthquake, near Anchorage, of 1964 resulted in only 131 deaths. At the time few people lived in the area (Figure 1.1). Not size. Only about 2,000 people died in the 1960 Great Chilean earthquake, the largest earthquake ever recorded. The Indian Ocean earthquake of 2004 was one of the largest ever, but most of the 230,000 fatalities were caused by the tsunami, not the earthquake itself. Ground type. Solid bedrock vibrates less than soft sediments, so there is less damage on bedrock. Sediments that are saturated with water undergo liquefaction and become like quicksand (Figure 1.2). Soil on a hillside may become a landslide. Liquefaction of sediments in Mexico City caused the collapse of many buildings in the 1985 earthquake. | text | null |
L_0135 | earthquake damage | T_1085 | In earthquake-prone areas, city planners try to reduce hazards. For example, in the San Francisco Bay Area, maps show how much shaking is expected for different ground types (Figure 1.3). This allows planners to locate new hospitals and schools more safely. The expected Modified Mercalli Intensity Scale for an earthquake of magnitude 7.1 on the northern portion of the Hayward Fault. Click image to the left or use the URL below. URL: | text | null |
L_0136 | earthquake safe structures | T_1086 | New construction can be made safer in many ways: Skyscrapers and other large structures built on soft ground must be anchored to bedrock, even if it lies hundreds of meters below the ground surface. The correct building materials must be used. Houses should bend and sway. Wood and steel are better than brick, stone, and adobe, which are brittle and will break. Larger buildings must sway, but not so much that they touch nearby buildings. Counterweights and diagonal steel beams are used to hold down sway. Large buildings can be placed on rollers so that they move with the ground. Buildings may be placed on layers of steel and rubber to absorb the shock of the waves. Connections, such as where the walls meet the foundation, must be made strong. In a multi-story building, the first story must be well supported (Figure 1.1). The first floor of this San Francisco build- ing is collapsing after the 1989 Loma Pri- eta earthquake. | text | null |
L_0136 | earthquake safe structures | T_1087 | To make older buildings more earthquake safe, retrofitting with steel or wood can reinforce a buildings structure and its connections. Elevated freeways and bridges can also be retrofitted so that they do not collapse. Steel trusses were built diagonally and horizontally across windows to retrofit a building at Stanford University in Palo Alto, California. The San Andreas Fault passes just west of the university. | text | null |
L_0136 | earthquake safe structures | T_1088 | Fires often cause more damage than the earthquake. Fires start because seismic waves rupture gas and electrical lines, and breaks in water mains make it difficult to fight the fires (Figure 1.3). Builders zigzag pipes so that they bend and flex when the ground shakes. In San Francisco, water and gas pipelines are separated by valves so that areas can be isolated if one segment breaks. | text | null |
L_0136 | earthquake safe structures | T_1089 | Why arent all structures in earthquakes zones constructed for maximum safety? Cost, of course. More sturdy structures are much more expensive to build. So communities must weigh how great the hazard is, what different In the 1906 San Francisco earthquake, fire was much more destructive than the ground shaking. building strategies cost, and make an informed decision. In 1868 marked the Hayward Fault erupted in what would be a disastrous earthquake today. Since the fault erupts every 140 years on average, East Bay residents and geologists are working to prepare for the inevitable event. Click image to the left or use the URL below. URL: | text | null |
L_0137 | earthquake zones | T_1090 | In a single year, on average, more than 900,000 earthquakes are recorded and 150,000 of them are strong enough to be felt. Each year about 18 earthquakes are major, with a Richter magnitude of 7.0 to 7.9, and on average one earthquake has a magnitude of 8 to 8.9. Magnitude 9 earthquakes are rare. The United States Geological Survey lists five since 1900 (see Figure 1.1 and Table 1.1). All but the Great Indian Ocean Earthquake of 2004 occurred somewhere around the Pacific Ocean basin. Location Valdivia, Chile Prince William Sound, Alaska Great Indian Ocean Earthquake Kamchatka, Alaska Tohoku, Japan Year 1960 1964 2004 1952 2011 Magnitude 9.5 9.2 9.1 9.0 9.0 The 1964 Good Friday Earthquake cen- tered in Prince William Sound, Alaska re- leased the second most amount of energy of any earthquake in recorded history. | text | null |
L_0137 | earthquake zones | T_1091 | Nearly 95% of all earthquakes take place along one of the three types of plate boundaries. About 80% of all earthquakes strike around the Pacific Ocean basin because it is lined with convergent and transform boundaries (Figure 1.2). About 15% take place in the Mediterranean-Asiatic Belt, where convergence is causing the Indian Plate to run into the Eurasian Plate. The remaining 5% are scattered around other plate boundaries or are intraplate earthquakes. Earthquake epicenters for magnitude 8.0 and greater events since 1900. The earthquake depth shows that most large quakes are shallow focus, but some sub- ducted plates cause deep focus quakes. | text | null |
L_0138 | earthquakes at convergent plate boundaries | T_1092 | Earthquakes at convergent plate boundaries mark the motions of subducting lithosphere as it plunges through the mantle (Figure 1.1). Eventually the plate heats up enough deform plastically and earthquakes stop. Convergent plate boundaries produce earthquakes all around the Pacific Ocean basin. | text | null |
L_0138 | earthquakes at convergent plate boundaries | T_1093 | Earthquakes in Japan are caused by ocean-ocean convergence. The Philippine Plate and the Pacific Plate subduct beneath oceanic crust on the North American or Eurasian plates. This complex plate tectonics situation creates a chain of volcanoes, the Japanese islands, and as many as 1,500 earthquakes annually. In March 2011 an enormous 9.0 earthquake struck off of Sendai in northeastern Japan. This quake, called the 2011 Tohoku earthquake, was the most powerful ever to strike Japan and one of the top five known in the world. Damage from the earthquake was nearly overshadowed by the tsunami it generated, which wiped out coastal cities and towns This cross section of earthquake epicen- ters with depth outlines the subducting plate with shallow, intermediate, and deep earthquakes. (Figure 1.2). Several months after the earthquake, about 22,000 people were dead or missing, and 190,000 buildings had been damaged or destroyed. Aftershocks, some as large as major earthquakes, have continued to rock the region. Destruction in Ofunato, Japan, from the 2011 Tohoku Earthquake. | text | null |
L_0138 | earthquakes at convergent plate boundaries | T_1093 | Earthquakes in Japan are caused by ocean-ocean convergence. The Philippine Plate and the Pacific Plate subduct beneath oceanic crust on the North American or Eurasian plates. This complex plate tectonics situation creates a chain of volcanoes, the Japanese islands, and as many as 1,500 earthquakes annually. In March 2011 an enormous 9.0 earthquake struck off of Sendai in northeastern Japan. This quake, called the 2011 Tohoku earthquake, was the most powerful ever to strike Japan and one of the top five known in the world. Damage from the earthquake was nearly overshadowed by the tsunami it generated, which wiped out coastal cities and towns This cross section of earthquake epicen- ters with depth outlines the subducting plate with shallow, intermediate, and deep earthquakes. (Figure 1.2). Several months after the earthquake, about 22,000 people were dead or missing, and 190,000 buildings had been damaged or destroyed. Aftershocks, some as large as major earthquakes, have continued to rock the region. Destruction in Ofunato, Japan, from the 2011 Tohoku Earthquake. | text | null |
L_0138 | earthquakes at convergent plate boundaries | T_1094 | The Pacific Northwest of the United States is at risk from a potentially massive earthquake that could strike any time. The subduction of three small plates beneath North America produces active volcanoes, the Cascades. As with an active subduction zone, there are also earthquakes. Surprisingly, large earthquakes only hit every 300 to 600 years. The last was in 1700, with an estimated magnitude of around 9. A quake of that magnitude today could produce an incredible amount of destruction and untold fatalities. | text | null |
L_0138 | earthquakes at convergent plate boundaries | T_1095 | Massive earthquakes are the hallmark of the thrust faulting and folding when two continental plates converge (Figure injured or homeless. Damage from the 2005 Kashmir earth- quake. 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_0139 | earthquakes at transform plate boundaries | T_1096 | Deadly earthquakes occur at transform plate boundaries. Transform faults have shallow focus earthquakes. Why do you think this is so? | text | null |
L_0139 | earthquakes at transform plate boundaries | T_1097 | As you learned in the chapter Plate Tectonics, the boundary between the Pacific and North American plates runs through much of California as the San Andreas Fault zone. As you can see in the (Figure 1.1), there is more than just one fault running through the area. There is really a fault zone. The San Andreas Fault runs from south to north up the peninsula, through San Francisco, gets through part of Marin north of the bay, and then goes out to sea. The other faults are part of the fault zone, and they too can be deadly. The faults along the San Andreas Fault zone produce around 10,000 earthquakes a year. Most are tiny, but occasion- ally one is massive. In the San Francisco Bay Area, the Hayward Fault was the site of a magnitude 7.0 earthquake in 1868. The 1906 quake on the San Andreas Fault had a magnitude estimated at about 7.9 (Figure 1.1). About 3,000 people died and 28,000 buildings were lost, mostly in the fire that followed the earthquake. (a) The San Andreas Fault zone in the San Francisco Bay Area. (b) The 1906 San Francisco earthquake is still the most costly natural disaster in California history. Recent California earthquakes occurred in: 1989: Loma Prieta earthquake near Santa Cruz, California. Magnitude 7.1 quake, 63 deaths, 3,756 injuries, 12,000+ people homeless, property damage about $6 billion. 1994: Northridge earthquake on a blind thrust fault near Los Angeles. Magnitude 6.7, 72 deaths, 12,000 injuries, damage estimated at $12.5 billion. In this video, the boundaries between three different tectonic plates and the earthquakes that result from their interactions are explored. Click image to the left or use the URL below. URL: | text | null |
L_0139 | earthquakes at transform plate boundaries | T_1098 | New Zealand also has a transform fault with strike-slip motion, causing about 20,000 earthquakes a year! Only a small percentage of those are large enough to be felt. A 6.3 quake in Christchurch in February 2011 killed about 180 people. | text | null |
L_0141 | earths crust | T_1100 | Earths outer surface is its crust, a cold, thin, brittle outer shell made of rock. The crust is very thin relative to the radius of the planet. There are two very different types of crust, each with its own distinctive physical and chemical properties, which are summarized in Table 1.1. Crust Oceanic Continental Thickness 5-12 km (3-8 mi) Avg. 35 km (22 mi) Density 3.0 g/cm3 2.7 g/cm3 Composition Mafic Felsic Rock types Basalt and gabbro All types | text | null |
L_0141 | earths crust | T_1101 | Oceanic crust is composed of mafic magma that erupts on the seafloor to create basalt lava flows or cools deeper down to create the intrusive igneous rock gabbro (Figure 1.1). Gabbro from ocean crust. The gabbro is deformed because of intense faulting at the eruption site. Sediments, primarily mud and the shells of tiny sea creatures, coat the seafloor. Sediment is thickest near the shore, where it comes off the continents in rivers and on wind currents. The oceanic crust is relatively thin and lies above the mantle. The cross section of oceanic crust in the Figure 1.2 shows the layers that grade from sediments at the top to extrusive basalt lava, to the sheeted dikes that feed lava to the surface, to deeper intrusive gabbro, and finally to the mantle. | text | null |
L_0141 | earths crust | T_1102 | Continental crust is made up of many different types of igneous, metamorphic, and sedimentary rocks. The average composition is granite, which is much less dense than the mafic rocks of the oceanic crust (Figure 1.3). Because it is thick and has relatively low density, continental crust rises higher on the mantle than oceanic crust, which sinks into the mantle to form basins. When filled with water, these basins form the planets oceans. Click image to the left or use the URL below. URL: A cross-section of oceanic crust. | text | null |
L_0143 | earths layers | T_1112 | The layers scientists recognize are pictured below (Figure 1.1). Core, mantle, and crust are divisions based on composition: 1. The crust is less than 1% of Earth by mass. The two types are oceanic crust and continental crust.Continental crust is felsic and oceanic crust is mafic. 2. The mantle is hot, ultramafic rock. It represents about 68% of Earths mass. 3. The core is mostly iron metal. The core makes up about 31% of the Earth. | text | null |
L_0143 | earths layers | T_1113 | Lithosphere and asthenosphere are divisions based on mechanical properties: 1. The lithosphere is composed of both the crust and the portion of the upper mantle and behaves as a brittle, rigid solid. 2. The asthenosphere is partially molten upper mantle material and behaves plastically and can flow. A cross section of Earth showing the fol- lowing layers: (1) crust (2) mantle (3a) outer core (3b) inner core (4) lithosphere (5) asthenosphere (6) outer core (7) inner core. 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_0145 | earths mantle | T_1116 | The two most important things about the mantle are: (1) it is made of solid rock, and (2) it is hot. | text | null |
L_0145 | earths mantle | T_1117 | Scientists know that the mantle is made of rock based on evidence from seismic waves, heat flow, and meteorites. The properties fit the ultramafic rock peridotite, which is made of the iron- and magnesium-rich silicate minerals (Figure 1.1). Peridotite is rarely found at Earths surface. | text | null |
L_0145 | earths mantle | T_1118 | Scientists know that the mantle is extremely hot because of the heat flowing outward from it and because of its physical properties. Heat flows in two different ways within the Earth: 1. Conduction: Heat is transferred through rapid collisions of atoms, which can only happen if the material is solid. Heat flows from warmer to cooler places until all are the same temperature. The mantle is hot mostly because of heat conducted from the core. Peridotite is formed of crystals of olivine (green) and pyroxene (black). 2. Convection: If a material is able to move, even if it moves very slowly, convection currents can form. Convection in the mantle is the same as convection in a pot of water on a stove. Convection currents within Earths mantle form as material near the core heats up. As the core heats the bottom layer of mantle material, particles move more rapidly, decreasing its density and causing it to rise. The rising material begins the convection current. When the warm material reaches the surface, it spreads horizontally. The material cools because it is no longer near the core. It eventually becomes cool and dense enough to sink back down into the mantle. At the bottom of the mantle, the material travels horizontally and is heated by the core. It reaches the location where warm mantle material rises, and the mantle convection cell is complete (Figure 1.2). Convection. | text | null |
L_0145 | earths mantle | T_1118 | Scientists know that the mantle is extremely hot because of the heat flowing outward from it and because of its physical properties. Heat flows in two different ways within the Earth: 1. Conduction: Heat is transferred through rapid collisions of atoms, which can only happen if the material is solid. Heat flows from warmer to cooler places until all are the same temperature. The mantle is hot mostly because of heat conducted from the core. Peridotite is formed of crystals of olivine (green) and pyroxene (black). 2. Convection: If a material is able to move, even if it moves very slowly, convection currents can form. Convection in the mantle is the same as convection in a pot of water on a stove. Convection currents within Earths mantle form as material near the core heats up. As the core heats the bottom layer of mantle material, particles move more rapidly, decreasing its density and causing it to rise. The rising material begins the convection current. When the warm material reaches the surface, it spreads horizontally. The material cools because it is no longer near the core. It eventually becomes cool and dense enough to sink back down into the mantle. At the bottom of the mantle, the material travels horizontally and is heated by the core. It reaches the location where warm mantle material rises, and the mantle convection cell is complete (Figure 1.2). Convection. | text | null |
L_0147 | earths tectonic plates | T_1120 | What portion of Earth makes up the plates in plate tectonics? Again, the answer came about in part due to war. In this case, the Cold War. During the 1950s and early 1960s, scientists set up seismograph networks to see if enemy nations were testing atomic bombs. These seismographs also recorded all of the earthquakes around the planet. The seismic records were used to locate an earthquakes epicenter, the point on Earths surface directly above the place where the earthquake occurs. Why is this relevant? It turns out that earthquake epicenters outline the plates. This is because earthquakes occur everywhere plates come into contact with each other. The lithosphere is divided into a dozen major and several minor plates (Figure 1.1). A single plate can be made of all oceanic lithosphere or all continental lithosphere, but nearly all plates are made of a combination of both. The movement of the plates over Earths surface is termed plate tectonics. Plates move at a rate of a few centimeters a year, about the same rate fingernails grow. | text | null |
L_0147 | earths tectonic plates | T_1121 | If seafloor spreading drives the plates, what drives seafloor spreading? This goes back to Arthur Holmes idea of mantle convection. Picture two convection cells side by side in the mantle, similar to the illustration in Figure 1.2. 1. Hot mantle from the two adjacent cells rises at the ridge axis, creating new ocean crust. 2. The top limb of the convection cell moves horizontally away from the ridge crest, as does the new seafloor. 3. The outer limbs of the convection cells plunge down into the deeper mantle, dragging oceanic crust as well. This takes place at the deep sea trenches. 4. The material sinks to the core and moves horizontally. 5. The material heats up and reaches the zone where it rises again. | text | null |
L_0147 | earths tectonic plates | T_1122 | Plate boundaries are the edges where two plates meet. How can two plates move relative to each other? Most geologic activities, including volcanoes, earthquakes, and mountain building, take place at plate boundaries. The features found at these plate boundaries are the mid-ocean ridges, trenches, and large transform faults (Figure 1.3). Divergent plate boundaries: the two plates move away from each other. Convergent plate boundaries: the two plates move towards each other. Transform plate boundaries: the two plates slip past each other. The type of plate boundary and the type of crust found on each side of the boundary determines what sort of geologic activity will be found there. We can visit each of these types of plate boundaries on land or at sea. | text | null |
L_0153 | effusive eruptions | T_1136 | Mafic magma creates gentler effusive eruptions. Although the pressure builds enough for the magma to erupt, it does not erupt with the same explosive force as felsic magma. Magma pushes toward the surface through fissures. Eventually, the magma reaches the surface and erupts through a vent (Figure 1.1). Effusive eruptions are common in Hawaii, where lavas are mafic. In effusive eruptions, lava flows readily, producing rivers of molten rock. A Quicktime movie with thermal camera of a lava stream within the vent of a Hawaiian volcano is seen here: | text | null |
L_0153 | effusive eruptions | T_1137 | Low-viscosity lava flows down mountainsides. Differences in composition and where the lavas erupt result in three types of lava flow coming from effusive eruptions. Aa lava forms a thick and brittle crust that is torn into rough and jagged pieces. Aa lava can spread over large areas as the lava continues to flow underneath the crusts surface. Pahoehoe lava forms lava tubes where fluid lava flows through the outer cooled rock crust. Pahoehoe lava is less viscous than aa lava, so its surface looks is smooth and ropy. Mafic lava that erupts underwater creates pillow lava. The lava cools very quickly, forming roughly spherical rocks. Pillow lava is common at mid-ocean ridges (Figure (a) Aa lava spread over large areas. (b) Pahoehoe lava tubes where at the Thurston Lava Tube in Hawaii Volcanoes National Park. (c) Pahoehoe lava is less viscous than aa lava so its surface looks is smooth and ropy. (d) Pillow lava. | text | null |
L_0153 | effusive eruptions | T_1138 | People can usually be evacuated before an effusive eruption, so they are much less deadly. Although effusive eruptions rarely kill anyone, they can be destructive. Even when people know that a lava flow is approaching, there is not much anyone can do to stop it from destroying a building or road (Figure 1.3). | text | null |
L_0159 | evolution of simple cells | T_1149 | Simple organic molecules such as proteins and nucleic acids eventually became complex organic substances. Sci- entists think that the organic molecules adhered to clay minerals, which provided the structure needed for these substances to organize. The clays, along with their metal cations, catalyzed the chemical reactions that caused the molecules to form polymers. The first RNA fragments could also have come together on ancient clays. E. coli (Escherichia coli) is a primitive prokaryote that may resemble the earliest cells. For an organic molecule to become a cell, it must be able to separate itself from its environment. To enclose the molecule, a lipid membrane grew around the organic material. Eventually the molecules could synthesize their own organic material and replicate themselves. These became the first cells. | text | null |
L_0159 | evolution of simple cells | T_1150 | The earliest cells were prokaryotes (Figure 1.1). Although prokaryotes have a cell membrane, they lack a cell nucleus and other organelles. Without a nucleus, RNA was loose within the cell. Over time the cells became more complex. LUCA was a prokaryote but differed from the first living cells because its genetic code was based on DNA. The oldest fossils are tiny microbe-like objects that are 3.5 billion years old. Evidence for bacteria, the first single-celled life forms, goes back 3.5 billion years (Figure 1.2). | text | null |
L_0159 | evolution of simple cells | T_1151 | The earliest life forms did not have the ability to photosynthesize. Without photosynthesis what did the earliest cells eat? Most likely they absorbed the nutrients that floated around in the organic soup that surrounded them. After hundreds of millions of years, these nutrients would have become less abundant. Sometime around 3 billion years ago (about 1.5 billion years after Earth formed!), photosynthesis began. Photo- synthesis allowed organisms to use sunlight and inorganic molecules, such as carbon dioxide and water, to create chemical energy that they could use for food. To photosynthesize, a cell needs chloroplasts (Figure 1.3). A diagram of a bacterium. Chloroplasts are visible in these cells found within a moss. | text | null |
L_0159 | evolution of simple cells | T_1151 | The earliest life forms did not have the ability to photosynthesize. Without photosynthesis what did the earliest cells eat? Most likely they absorbed the nutrients that floated around in the organic soup that surrounded them. After hundreds of millions of years, these nutrients would have become less abundant. Sometime around 3 billion years ago (about 1.5 billion years after Earth formed!), photosynthesis began. Photo- synthesis allowed organisms to use sunlight and inorganic molecules, such as carbon dioxide and water, to create chemical energy that they could use for food. To photosynthesize, a cell needs chloroplasts (Figure 1.3). A diagram of a bacterium. Chloroplasts are visible in these cells found within a moss. | text | null |
L_0159 | evolution of simple cells | T_1152 | In what two ways did photosynthesis make the planet much more favorable for life? 1. Photosynthesis allowed organisms to create food energy so that they did not need to rely on nutrients floating around in the environment. Photosynthesizing organisms could also become food for other organisms. 2. A byproduct of photosynthesis is oxygen. When photosynthesis evolved, all of a sudden oxygen was present in large amounts in the atmosphere. For organisms used to an anaerobic environment, the gas was toxic, and many organisms died out. 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_0159 | evolution of simple cells | T_1153 | What were these organisms that completely changed the progression of life on Earth by changing the atmosphere from anaerobic to aerobic? The oldest known fossils that are from organisms known to photosynthesize are cyanobac- teria. Cyanobacteria were present by 2.8 billion years ago, and some may have been around as far back as 3.5 billion years. Cyanobacteria were the dominant life forms in the Archean. Why would such a primitive life-form have been dominant in the Precambrian? Many cyanobacteria lived in reef-like structures known as stromatolites (Figure These rocks in Glacier National Park, Montana may contain some of the oldest fossil microbes on Earth. Modern cyanobacteria are also called blue-green algae. These organisms may consist of a single or many cells and they are found in many different environments (Figure 1.5). Even now cyanobacteria account for 20% to 30% of photosynthesis on Earth. A large bloom of cyanobacteria is harmful to this lake. | text | null |
L_0159 | evolution of simple cells | T_1153 | What were these organisms that completely changed the progression of life on Earth by changing the atmosphere from anaerobic to aerobic? The oldest known fossils that are from organisms known to photosynthesize are cyanobac- teria. Cyanobacteria were present by 2.8 billion years ago, and some may have been around as far back as 3.5 billion years. Cyanobacteria were the dominant life forms in the Archean. Why would such a primitive life-form have been dominant in the Precambrian? Many cyanobacteria lived in reef-like structures known as stromatolites (Figure These rocks in Glacier National Park, Montana may contain some of the oldest fossil microbes on Earth. Modern cyanobacteria are also called blue-green algae. These organisms may consist of a single or many cells and they are found in many different environments (Figure 1.5). Even now cyanobacteria account for 20% to 30% of photosynthesis on Earth. A large bloom of cyanobacteria is harmful to this lake. | text | null |
L_0163 | explosive eruptions | T_1162 | A large explosive eruption creates even more devastation than the force of the atom bomb dropped on Nagasaki at the end of World War II, in which more than 40,000 people died. A large explosive volcanic eruption is 10,000 times as powerful. Explosive eruptions are found at the convergent plate boundaries that line parts of western North America, resulting in the Cascades in the Pacific Northwest and the Aleutians in Alaska. | text | null |
L_0163 | explosive eruptions | T_1163 | Explosive eruptions are caused by gas-rich, felsic magmas that churn within the magma chamber. When the pressure becomes too great the magma breaks through the rock above the chamber and explodes, just like when a cork is released from a bottle of champagne. Magma, rock, and ash burst upward in an enormous explosion (Figure 1.1). | text | null |
L_0163 | explosive eruptions | T_1164 | The erupted rock fragments are called tephra. Ash and gas also explode from the volcano. Scorching hot tephra, ash, and gas may speed down the volcanos slopes at 700 km/h (450 mph) as a pyroclastic flow. Pyroclastic means fire rock (Figure 1.2). Left: An explosive eruption from the Mayon Volcano in the Philippines in 1984. Ash flies upward into the sky and pyroclastic flows pour down the mountainside. Right: The end of a pyroclastic flow at Mount St. Helens. Pyroclastic flows knock down everything in their path. The temperature inside a pyroclastic flow may be as high as 1,000 C (1,800 F). Blowdown of trees near Mount St. Helens shows the direction of the blast and pyro- clastic flow. | text | null |
L_0163 | explosive eruptions | T_1164 | The erupted rock fragments are called tephra. Ash and gas also explode from the volcano. Scorching hot tephra, ash, and gas may speed down the volcanos slopes at 700 km/h (450 mph) as a pyroclastic flow. Pyroclastic means fire rock (Figure 1.2). Left: An explosive eruption from the Mayon Volcano in the Philippines in 1984. Ash flies upward into the sky and pyroclastic flows pour down the mountainside. Right: The end of a pyroclastic flow at Mount St. Helens. Pyroclastic flows knock down everything in their path. The temperature inside a pyroclastic flow may be as high as 1,000 C (1,800 F). Blowdown of trees near Mount St. Helens shows the direction of the blast and pyro- clastic flow. | text | null |
L_0163 | explosive eruptions | T_1165 | Prior to the Mount St. Helens eruption in 1980, the Lassen Peak eruption on May 22, 1915, was the most recent Cascades eruption. A column of ash and gas shot 30,000 feet into the air. This triggered a high-speed pyroclastic flow, which melted snow and created a volcanic mudflow known as a lahar. Lassen Peak currently has geothermal activity and could erupt explosively again. Mt. Shasta, the other active volcano in California, erupts every 600 to 800 years. An eruption would most likely create a large pyroclastic flow, and probably a lahar. Of course, Mt. Shasta could explode and collapse like Mt. Mazama in Oregon (Figure 1.4). Crater Lake fills the caldera of the col- lapsed Mt. Mazama, which erupted with 42 times more power than Mount St. He- lens in 1980. The bathymetry of the lake shows volcanic features such as cinder cones. | text | null |
L_0163 | explosive eruptions | T_1166 | Volcanic gases can form poisonous and invisible clouds in the atmosphere. These gases may contribute to environ- mental problems such as acid rain and ozone destruction. Particles of dust and ash may stay in the atmosphere for years, disrupting weather patterns and blocking sunlight (Figure 1.5). The ash plume from Eyjafjallajkull vol- cano in Iceland disrupted air travel across Europe for six days in April 2010. Click image to the left or use the URL below. URL: | text | null |
L_0166 | finding and mining ores | T_1174 | Some minerals are very useful. An ore is a rock that contains minerals with useful elements. Aluminum in bauxite ore (Figure 1.1) is extracted from the ground and refined to be used in aluminum foil and many other products. The cost of creating a product from a mineral depends on how abundant the mineral is and how much the extraction and refining processes cost. Environmental damage from these processes is often not figured into a products cost. It is important to use mineral resources wisely. | text | null |
L_0166 | finding and mining ores | T_1175 | Geologic processes create and concentrate minerals that are valuable natural resources. Geologists study geological formations and then test the physical and chemical properties of soil and rocks to locate possible ores and determine their size and concentration. A mineral deposit will only be mined if it is profitable. A concentration of minerals is only called an ore deposit if it is profitable to mine. There are many ways to mine ores. Aluminum is made from the aluminum- bearing minerals in bauxite. | text | null |
L_0166 | finding and mining ores | T_1176 | Surface mining allows extraction of ores that are close to Earths surface. Overlying rock is blasted and the rock that contains the valuable minerals is placed in a truck and taken to a refinery. As pictured in Figure 1.2, surface mining includes open-pit mining and mountaintop removal. Other methods of surface mining include strip mining, placer mining, and dredging. Strip mining is like open pit mining but with material removed along a strip. These different forms of surface mining are methods of extracting ores close to Earths surface. Placers are valuable minerals found in stream gravels. Californias nickname, the Golden State, can be traced back to the discovery of placer deposits of gold in 1848. The gold weathered out of hard metamorphic rock in the western Sierra Nevada, which also contains deposits of copper, lead, zinc, silver, chromite, and other valuable minerals. The | text | null |
L_0166 | finding and mining ores | T_1177 | Underground mining is used to recover ores that are deeper into Earths surface. Miners blast and tunnel into rock to gain access to the ores. How underground mining is approached from above, below, or sideways depends on the placement of the ore body, its depth, the concentration of ore, and the strength of the surrounding rock. Underground mining is very expensive and dangerous. Fresh air and lights must also be brought into the tunnels for the miners, and accidents are far too common. | text | null |
L_0166 | finding and mining ores | T_1178 | The ores journey to becoming a useable material is only just beginning when the ore leaves the mine (Figure separated out of the ore. A few methods for extracting ore are: heap leaching: the addition of chemicals, such as cyanide or acid, to remove ore. flotation: the addition of a compound that attaches to the valuable mineral and floats. smelting: roasting rock, causing it to segregate into layers so the mineral can be extracted. To extract the metal from the ore, the rock is melted at a temperature greater than 900o C, which requires a lot of energy. Extracting metal from rock is so energy-intensive that if you recycle just 40 aluminum cans, you will save the energy equivalent of one gallon of gasoline. | text | null |
L_0209 | intraplate activity | T_1333 | A small amount of geologic activity, known as intraplate activity, does not take place at plate boundaries but within a plate instead. Mantle plumes are pipes of hot rock that rise through the mantle. The release of pressure causes melting near the surface to form a hotspot. Eruptions at the hotspot create a volcano. Hotspot volcanoes are found in a line (Figure 1.1). Can you figure out why? Hint: The youngest volcano sits above the hotspot and volcanoes become older with distance from the hotspot. | text | null |
L_0209 | intraplate activity | T_1334 | The first photo above is of a volcanic eruption in Hawaii. Hawaii is not in western North America, but is in the central Pacific ocean, near the middle of the Pacific Plate. The Hawaiian Islands are a beautiful example of a hotspot chain in the Pacific Ocean. Kilauea volcano lies above the Hawaiian hotspot. Mauna Loa volcano is older than Kilauea and is still erupting, but at a slower rate. The islands get progressively older to the northwest because they are further from the hotspot. This is because the Pacific Plate is moving toward the northwest over the hotspot. Loihi, the youngest volcano, is still below the sea surface. Since many hotspots are stationary in the mantle, geologists can use some hotspot chains to tell the direction and the speed a plate is moving (Figure 1.2). The Hawaiian chain continues into the Emperor Seamounts. The bend in the chain was caused by a change in the direction of the Pacific Plate 43 million years ago. Using the age and distance of the bend, geologists can figure out the speed of the Pacific Plate over the hotspot. The Hawaiian Islands have formed from volcanic eruptions above the Hawaii hotspot. | text | null |
L_0209 | intraplate activity | T_1334 | The first photo above is of a volcanic eruption in Hawaii. Hawaii is not in western North America, but is in the central Pacific ocean, near the middle of the Pacific Plate. The Hawaiian Islands are a beautiful example of a hotspot chain in the Pacific Ocean. Kilauea volcano lies above the Hawaiian hotspot. Mauna Loa volcano is older than Kilauea and is still erupting, but at a slower rate. The islands get progressively older to the northwest because they are further from the hotspot. This is because the Pacific Plate is moving toward the northwest over the hotspot. Loihi, the youngest volcano, is still below the sea surface. Since many hotspots are stationary in the mantle, geologists can use some hotspot chains to tell the direction and the speed a plate is moving (Figure 1.2). The Hawaiian chain continues into the Emperor Seamounts. The bend in the chain was caused by a change in the direction of the Pacific Plate 43 million years ago. Using the age and distance of the bend, geologists can figure out the speed of the Pacific Plate over the hotspot. The Hawaiian Islands have formed from volcanic eruptions above the Hawaii hotspot. | text | null |
L_0209 | intraplate activity | T_1335 | The second photo in the introduction is of a geyser at Yellowstone National Park in Wyoming. Yellowstone is in the western U.S. but is inland from the plate boundaries offshore. Hotspot magmas rarely penetrate through thick continental crust, so hotspot activity on continents is rare. One exception is the Yellowstone hotspot (Figure 1.3). Volcanic activity above the Yellowstone hotspot on can be traced from 15 million years ago to its present location on the North American Plate. The ages of volcanic activity attributed to the Yellowstone hotspot. Click image to the left or use the URL below. URL: | text | null |
L_0210 | intraplate earthquakes | T_1336 | Intraplate earthquakes are the result of stresses caused by plate motions acting in solid slabs of lithosphere. The earthquakes take place along ancient faults or rift zones that have been weakened by activity that may have taken place hundreds of millions of years ago. | text | null |
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