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L_0110 | climate change in earth history | T_0995 | Climate has changed throughout Earth history. Much of the time Earths climate was hotter and more humid than it is today, but climate has also been colder, as when glaciers covered much more of the planet. The most recent ice ages were in the Pleistocene Epoch, between 1.8 million and 10,000 years ago (Figure 1.1). Glaciers advanced and retreated in cycles, known as glacial and interglacial periods. With so much of the worlds water bound into the ice, sea level was about 125 meters (395 feet) lower than it is today. Many scientists think that we are now in a warm, interglacial period that has lasted about 10,000 years. For the past 1500 years, climate has been relatively mild and stable when compared with much of Earths history. Why has climate stability been beneficial for human civilization? Stability has allowed the expansion of agriculture and the development of towns and cities. Fairly small temperature changes can have major effects on global climate. The average global temperature during glacial periods was only about 5.5o C (10o F) less than Earths current average temperature. Temperatures during the interglacial periods were about 1.1o C (2.0o F) higher than today (Figure 1.2). The maximum extent of Northern Hemi- sphere glaciers during the Pleistocene epoch. Since the end of the Pleistocene, the global average temperature has risen about 4o C (7o F). Glaciers are retreating and sea level is rising. While climate is getting steadily warmer, there have been a few more extreme warm and cool times in the last 10,000 years. Changes in climate have had effects on human civilization. The Medieval Warm Period from 900 to 1300 A.D. allowed Vikings to colonize Greenland and Great Britain to grow wine grapes. The Little Ice Age, from the 14th to 19th centuries, the Vikings were forced out of Greenland and humans had to plant crops further south. The graph is a compilation of 5 recon- structions (the green line is the mean of the five records) of mean temperature changes. This illustrates the high tem- peratures of the Medieval Warm Period, the lows of the Little Ice Age, and the very high (and climbing) temperature of this decade. Click image to the left or use the URL below. URL: | text | null |
L_0110 | climate change in earth history | T_0995 | Climate has changed throughout Earth history. Much of the time Earths climate was hotter and more humid than it is today, but climate has also been colder, as when glaciers covered much more of the planet. The most recent ice ages were in the Pleistocene Epoch, between 1.8 million and 10,000 years ago (Figure 1.1). Glaciers advanced and retreated in cycles, known as glacial and interglacial periods. With so much of the worlds water bound into the ice, sea level was about 125 meters (395 feet) lower than it is today. Many scientists think that we are now in a warm, interglacial period that has lasted about 10,000 years. For the past 1500 years, climate has been relatively mild and stable when compared with much of Earths history. Why has climate stability been beneficial for human civilization? Stability has allowed the expansion of agriculture and the development of towns and cities. Fairly small temperature changes can have major effects on global climate. The average global temperature during glacial periods was only about 5.5o C (10o F) less than Earths current average temperature. Temperatures during the interglacial periods were about 1.1o C (2.0o F) higher than today (Figure 1.2). The maximum extent of Northern Hemi- sphere glaciers during the Pleistocene epoch. Since the end of the Pleistocene, the global average temperature has risen about 4o C (7o F). Glaciers are retreating and sea level is rising. While climate is getting steadily warmer, there have been a few more extreme warm and cool times in the last 10,000 years. Changes in climate have had effects on human civilization. The Medieval Warm Period from 900 to 1300 A.D. allowed Vikings to colonize Greenland and Great Britain to grow wine grapes. The Little Ice Age, from the 14th to 19th centuries, the Vikings were forced out of Greenland and humans had to plant crops further south. The graph is a compilation of 5 recon- structions (the green line is the mean of the five records) of mean temperature changes. This illustrates the high tem- peratures of the Medieval Warm Period, the lows of the Little Ice Age, and the very high (and climbing) temperature of this decade. Click image to the left or use the URL below. URL: | text | null |
L_0111 | climate zones and biomes | T_0996 | The major factors that influence climate determine the different climate zones. In general, the same type of climate zone will be found at similar latitudes and in similar positions on nearly all continents, both in the Northern and Southern Hemispheres. The exceptions to this pattern are the climate zones called the continental climates, which are not found at higher latitudes in the Southern Hemisphere. This is because the Southern Hemisphere land masses are not wide enough to produce a continental climate. | text | null |
L_0111 | climate zones and biomes | T_0997 | Climate zones are classified by the Kppen classification system. This system is based on the temperature, the amount of precipitation, and the times of year when precipitation occurs. Since climate determines the type of vegetation that grows in an area, vegetation is used as an indicator of climate type. | text | null |
L_0111 | climate zones and biomes | T_0998 | A climate type and its plants and animals make up a biome. The organisms of a biome share certain characteristics around the world, because their environment has similar advantages and challenges. The organisms have adapted to that environment in similar ways over time. For example, different species of cactus live on different continents, but they have adapted to the harsh desert in similar ways. Click image to the left or use the URL below. URL: | text | null |
L_0111 | climate zones and biomes | T_0999 | The Kppen classification system recognizes five major climate groups. Each group is divided into subcategories. Some of these subcategories are forest, monsoon, and wet/dry types, based on the amount of precipitation and season when that precipitation occurs (Figure 1.1). This world map of the Kppen classification system indicates where the climate zones and major biomes are located. | text | null |
L_0111 | climate zones and biomes | T_1000 | Tropical moist climates are found in a band about 15o to 25o N and S of the Equator (Figure 1.1). Temperature: Intense sunshine. Each month has an average temperature of at least 18o C (64o F). Rainfall: Abundant, at least 150 cm (59 inches) per year. The main vegetation for this climate is the tropical rainforest. | text | null |
L_0111 | climate zones and biomes | T_1001 | Dry climates have less precipitation than evaporation. Temperature: Abundant sunshine. Summer temperatures are high; winters are cooler and longer than in tropical moist climates. Rainfall: Irregular; several years of drought are often followed by a single year of abundant rainfall. Dry climates cover about 26% of the worlds land area. Low latitude deserts are found at the Ferrell cell high pressure zone. Higher latitude deserts occur within continents or in rainshadows. Vegetation is sparse but well adapted to the dry conditions. | text | null |
L_0111 | climate zones and biomes | T_1002 | Moist subtropical mid-latitude climates are found along the coastal areas in the United States. Temperature: The coldest month ranges from just below freezing to almost balmy, between -3o C and 18o C (27o to 64o F). Summers are mild, with average temperatures above 10o C (50o F). Seasons are distinct. Rainfall: There is plentiful annual rainfall. | text | null |
L_0111 | climate zones and biomes | T_1003 | Continental climates are found in most of the North American interior from about 40 N to 70 N. Temperature: The average temperature of the warmest month is higher than 10 C (50 F) and the coldest month is below -3 C (27 F). Precipitation: Winters are cold and stormy (look at the latitude of this zone and see if you can figure out why). Snowfall is common and snow stays on the ground for long periods of time. Trees grow in continental climates, even though winters are extremely cold, because the average annual temperature is fairly mild. Continental climates are not found in the Southern Hemisphere because of the absence of a continent large enough to generate this effect. | text | null |
L_0111 | climate zones and biomes | T_1004 | Polar climates are found across the continents that border the Arctic Ocean, Greenland, and Antarctica. Temperature: Winters are entirely dark and bitterly cold. Summer days are long, but the Sun is low on the horizon so summers are cool. The average temperature of the warmest month is less than 10o C (50o F). The annual temperature range is large. Precipitation: The region is dry, with less than 25 cm (10 inches) of precipitation annually; most precipitation occurs during the summer. | text | null |
L_0111 | climate zones and biomes | T_1005 | When climate conditions in a small area are different from those of the surroundings, the climate of the small area is called a microclimate. The microclimate of a valley may be cool relative to its surroundings since cold air sinks. The ground surface may be hotter or colder than the air a few feet above it, because rock and soil gain and lose heat readily. Different sides of a mountain will have different microclimates. In the Northern Hemisphere, a south-facing slope receives more solar energy than a north-facing slope, so each side supports different amounts and types of vegetation. Altitude mimics latitude in climate zones. Climates and biomes typical of higher latitudes may be found in other areas of the world at high altitudes. Click image to the left or use the URL below. URL: | text | null |
L_0113 | coal power | T_1012 | Coal, a solid fossil fuel formed from the partially decomposed remains of ancient forests, is burned primarily to produce electricity. Coal use is undergoing enormous growth as the availability of oil and natural gas decreases and cost increases. This increase in coal use is happening particularly in developing nations, such as China, where coal is cheap and plentiful. Coal is black or brownish-black. The most common form of coal is bituminous, a sedimentary rock that contains impurities such as sulfur (Figure 1.1). Anthracite coal has been metamorphosed and is nearly all carbon. For this reason, anthracite coal burns more cleanly than bituminous coal. | text | null |
L_0113 | coal power | T_1013 | Coal forms from dead plants that settled at the bottom of ancient swamps. Lush coal swamps were common in the tropics during the Carboniferous period, which took place more than 300 million years ago (Figure 1.2). The climate was warmer then. Mud and other dead plants buried the organic material in the swamp, and burial kept oxygen away. When plants are buried without oxygen, the organic material can be preserved or fossilized. Sand and clay settling on top of the decaying plants squeezed out the water and other substances. Millions of years later, what remains is a carbon- containing rock that we know as coal. | text | null |
L_0113 | coal power | T_1014 | Around the world, coal is the largest source of energy for electricity. The United States is rich in coal (Figure 1.3). California once had a number of small coal mines, but the state no longer produces coal. To turn coal into electricity, the rock is crushed into powder, which is then burned in a furnace that has a boiler. Like other fuels, coal releases its energy as heat when it burns. Heat from the burning coal boils the water in the boiler to make steam. The steam spins turbines, which turn generators to create electricity. In this way, the energy stored in the coal is converted to useful energy like electricity. | text | null |
L_0113 | coal power | T_1015 | For coal to be used as an energy source, it must first be mined. Coal mining occurs at the surface or underground by methods that are described in the the chapter Materials of Earths Crust (Figure 1.4). Mining, especially underground The location of the continents during the Carboniferous period. Notice that quite a lot of land area is in the region of the tropics. mining, can be dangerous. In April 2010, 29 miners were killed at a West Virginia coal mine when gas that had accumulated in the mine tunnels exploded and started a fire. Coal mining exposes minerals and rocks from underground to air and water at the surface. Many of these minerals contain the element sulfur, which mixes with air and water to make sulfuric acid, a highly corrosive chemical. If the sulfuric acid gets into streams, it can kill fish, plants, and animals that live in or near the water. Click image to the left or use the URL below. URL: | text | null |
L_0114 | coastal pollution | T_1016 | Most ocean pollution comes as runoff from land and originates as agricultural, industrial, and municipal wastes (Figure 1.1). The remaining 20% of water pollution enters the ocean directly from oil spills and people dumping wastes directly into the water. Ships at sea empty their wastes directly into the ocean, for example. Coastal pollution can make coastal water unsafe for humans and wildlife. After rainfall, there can be enough runoff pollution that beaches must be closed to prevent the spread of disease from pollutants. A surprising number of beaches are closed because of possible health hazards each year. A large proportion of the fish we rely on for food live in the coastal wetlands or lay their eggs there. Coastal runoff from farm waste often carries water-borne organisms that cause lesions that kill fish. Humans who come in In some areas of the world, ocean pollution is all too obvious. contact with polluted waters and affected fish can also experience harmful symptoms. More than one-third of the shellfish-growing waters of the United States are adversely affected by coastal pollution. | text | null |
L_0114 | coastal pollution | T_1017 | Fertilizers that run off of lawns and farm fields are extremely harmful to the environment. Nutrients, such as nitrates, in the fertilizer promote algae growth in the water they flow into. With the excess nutrients, lakes, rivers, and bays become clogged with algae and aquatic plants. Eventually these organisms die and decompose. Decomposition uses up all the dissolved oxygen in the water. Without oxygen, large numbers of plants, fish, and bottom-dwelling animals die. Every year dead zones appear in lakes and nearshore waters. A dead zone is an area of hundreds of kilometers of ocean without fish or plant life. The Mississippi is not the only river that carries the nutrients necessary to cause a dead zone. Rivers that drain regions where human population density is high and where crops are grown create dead zones all over the world (Figure 1.2). | text | null |
L_0116 | comets | T_1025 | Comets are small, icy objects that have very elliptical orbits around the Sun. Their orbits carry them from the outer solar system to the inner solar system, close to the Sun. Early in Earths history, comets may have brought water and other substances to Earth during collisions. Comet tails form the outer layers of ice melt and evaporate as the comet flies close to the Sun. The ice from the comet vaporizes and forms a glowing coma, which reflects light from the Sun. Radiation and particles streaming from the Sun push this gas and dust into a long tail that always points away from the Sun (Figure 1.1). Comets appear for only a short time when they are near the Sun, then seem to disappear again as they move back to the outer solar system. Comet Hale-Bopp, also called the Great Comet of 1997, shone brightly for several months in 1997. The comet has two visible tails: a bright, curved dust tail and a fainter, straight tail of ions (charged atoms) pointing directly away from the Sun. The time between one appearance of a comet and the next is called the comets period. Halleys comet, with a period of 75 years, will next be seen in 2061. The first mention of the comet in historical records may go back as much as two millennia. | text | null |
L_0116 | comets | T_1026 | Short-period comets, with periods of about 200 years or less, come from a region beyond the orbit of Neptune called the Kuiper belt (pronounced KI-per). It contains not only comets, but also asteroids and at least two dwarf planets. Comets with periods as long as thousands or even millions of years come from a very distant region of the solar system called the Oort cloud, about 50,000 100,000 AU from the Sun (50,000 - 100,000 times the distance from the Sun to Earth). Click image to the left or use the URL below. URL: | text | null |
L_0118 | conserving water | T_1032 | Water consumption per person has been going down for the past few decades. There are many ways that water conservation can be encouraged. Charging more for water gives a financial incentive for careful water use. Water use may be restricted by time of day, season, or activity. Good behavior can be encouraged; for example, people can be given an incentive to replace grass with desert plants in arid regions. | text | null |
L_0118 | conserving water | T_1033 | As human population growth continues, water conservation will become increasingly important globally, especially in developed countries where people use an enormous amount of water. What are some of the ways you can conserve water in and around your home? Avoid polluting water so that less is needed. Convert to more efficient irrigation methods on farms and in gardens. Reduce household demand by installing water-saving devices such as low-flow shower heads and toilets. Reduce personal demand by turning off the tap when water is not being used and taking shorter showers. Engage in water-saving practices: for instance, water lawns less and sweep rather than hose down sidewalks. At Earth Summit 2002, many governments approved a Plan of Action to address the scarcity of water and safe drinking water in developing countries. One goal of this plan was to cut in half the number of people without access to safe drinking water by 2015. Although this is a very important goal, it will not be met. Goals like these are made more difficult as population continues to grow. This colorful adobe house in Tucson, Arizona is surrounded by native cactus, which needs little water to thrive. Click image to the left or use the URL below. URL: | text | null |
L_0119 | continental drift | T_1034 | Alfred Wegener, born in 1880, was a meteorologist and explorer. In 1911, Wegener found a scientific paper that listed identical plant and animal fossils on opposite sides of the Atlantic Ocean. Intrigued, he then searched for and found other cases of identical fossils on opposite sides of oceans. The explanation put out by the scientists of the day was that land bridges had once stretched between these continents. Instead, Wegener pondered the way Africa and South America appeared to fit together like puzzle pieces. Other scientists had suggested that Africa and South America had once been joined, but Wegener was the ideas most dogged supporter. Wegener amassed a tremendous amount of evidence to support his hypothesis that the continents had once been joined. Imagine that youre Wegeners colleague. What sort of evidence would you look for to see if the continents had actually been joined and had moved apart? | text | null |
L_0119 | continental drift | T_1035 | Here is the main evidence that Wegener and his supporters collected for the continental drift hypothesis: The continents appear to fit together. Ancient fossils of the same species of extinct plants and animals are found in rocks of the same age but are on continents that are now widely separated (Figure 1.1). Wegener proposed that the organisms had lived side by side, but that the lands had moved apart after they were dead and fossilized. His critics suggested that the organisms moved over long-gone land bridges, but Wegener thought that the organisms could not have been able to travel across the oceans. Fossils of the seed fern Glossopteris were too heavy to be carried so far by wind. Mesosaurus was a swimming reptile, but could only swim in fresh water. Cynognathus and Lystrosaurus were land reptiles and were unable to swim. Wegener used fossil evidence to support his continental drift hypothesis. The fos- sils of these organisms are found on lands that are now far apart. Identical rocks, of the same type and age, are found on both sides of the Atlantic Ocean. Wegener said the rocks had formed side by side and that the land had since moved apart. Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean. The Appalachians of the eastern United States and Canada, for example, are just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway (Figure 1.2). Wegener concluded that they formed as a single mountain range that was separated as the continents drifted. Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the Equator. This would indicate that the glaciers either formed in the middle of the ocean and/or covered most of the Earth. Today, glaciers only form on land and nearer the poles. Wegener thought that the glaciers were centered over the southern land mass close to the South Pole and the continents moved to their present positions later on. The similarities between the Appalachian and the eastern Greenland mountain ranges are evidences for the continental drift hypothesis. Coral reefs and coal-forming swamps are found in tropical and subtropical environments, but ancient coal seams and coral reefs are found in locations where it is much too cold today. Wegener suggested that these creatures were alive in warm climate zones and that the fossils and coal later drifted to new locations on the continents. Wegener thought that mountains formed as continents ran into each other. This got around the problem of the leading hypothesis of the day, which was that Earth had been a molten ball that bulked up in spots as it cooled (the problem with this idea was that the mountains should all be the same age and they were known not to be). Click image to the left or use the URL below. URL: | text | null |
L_0119 | continental drift | T_1035 | Here is the main evidence that Wegener and his supporters collected for the continental drift hypothesis: The continents appear to fit together. Ancient fossils of the same species of extinct plants and animals are found in rocks of the same age but are on continents that are now widely separated (Figure 1.1). Wegener proposed that the organisms had lived side by side, but that the lands had moved apart after they were dead and fossilized. His critics suggested that the organisms moved over long-gone land bridges, but Wegener thought that the organisms could not have been able to travel across the oceans. Fossils of the seed fern Glossopteris were too heavy to be carried so far by wind. Mesosaurus was a swimming reptile, but could only swim in fresh water. Cynognathus and Lystrosaurus were land reptiles and were unable to swim. Wegener used fossil evidence to support his continental drift hypothesis. The fos- sils of these organisms are found on lands that are now far apart. Identical rocks, of the same type and age, are found on both sides of the Atlantic Ocean. Wegener said the rocks had formed side by side and that the land had since moved apart. Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean. The Appalachians of the eastern United States and Canada, for example, are just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway (Figure 1.2). Wegener concluded that they formed as a single mountain range that was separated as the continents drifted. Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the Equator. This would indicate that the glaciers either formed in the middle of the ocean and/or covered most of the Earth. Today, glaciers only form on land and nearer the poles. Wegener thought that the glaciers were centered over the southern land mass close to the South Pole and the continents moved to their present positions later on. The similarities between the Appalachian and the eastern Greenland mountain ranges are evidences for the continental drift hypothesis. Coral reefs and coal-forming swamps are found in tropical and subtropical environments, but ancient coal seams and coral reefs are found in locations where it is much too cold today. Wegener suggested that these creatures were alive in warm climate zones and that the fossils and coal later drifted to new locations on the continents. Wegener thought that mountains formed as continents ran into each other. This got around the problem of the leading hypothesis of the day, which was that Earth had been a molten ball that bulked up in spots as it cooled (the problem with this idea was that the mountains should all be the same age and they were known not to be). Click image to the left or use the URL below. URL: | text | null |
L_0120 | coriolis effect | T_1036 | The Coriolis effect describes how Earths rotation steers winds and surface ocean currents (Figure 1.1). Coriolis causes freely moving objects to appear to move to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The objects themselves are actually moving straight, but the Earth is rotating beneath them, so they seem to bend or curve. Thats why it is incorrect to call Coriolis a force. It is not forcing anything to happen! An example might make the Coriolis effect easier to visualize. If an airplane flies 500 miles due north, it will not arrive at the city that was due north of it when it began its journey. Over the time it takes for the airplane to fly 500 miles, that city moved, along with the Earth it sits on. The airplane will therefore arrive at a city to the west of the original city (in the Northern Hemisphere), unless the pilot has compensated for the change. So to reach his intended destination, the pilot must also veer right while flying north. As wind or an ocean current moves, the Earth spins underneath it. As a result, an object moving north or south along the Earth will appear to move in a curve instead of in a straight line. Wind or water that travels toward the poles from the Equator is deflected to the east, while wind or water that travels toward the Equator from the poles gets bent to the west. The Coriolis effect bends the direction of surface currents to the right in the Northern Hemisphere and left in the Southern Hemisphere. The Coriolis effect causes winds and cur- rents to form circular patterns. The di- rection that they spin depends on the hemisphere that they are in. Coriolis effect is demonstrated using a metal ball and a rotating plate in this video. The ball moves in a circular path just like a freely moving particle of gas or liquid moves on the rotating Earth (5b). Click image to the left or use the URL below. URL: | text | null |
L_0121 | correlation using relative ages | T_1037 | Superposition and cross-cutting are helpful when rocks are touching one another and lateral continuity helps match up rock layers that are nearby. To match up rocks that are further apart we need the process of correlation. How do geologists correlate rock layers that are separated by greater distances? There are three kinds of clues: | text | null |
L_0121 | correlation using relative ages | T_1038 | 1. Distinctive rock formations may be recognizable across large regions (Figure 1.1). | text | null |
L_0121 | correlation using relative ages | T_1039 | 2. Two separated rock units with the same index fossil are of very similar age. What traits do you think an index fossil should have? To become an index fossil the organism must have (1) been widespread so that it is useful for identifying rock layers over large areas and (2) existed for a relatively brief period of time so that the approximate age of the rock layer is immediately known. Many fossils may qualify as index fossils (Figure below). Ammonites, trilobites, and graptolites are often used as index fossils. Microfossils, which are fossils of microscopic organisms, are also useful index fossils. Fossils of animals that drifted in the upper layers of the ocean are particularly useful as index fossils, since they may be distributed over very large areas. A biostratigraphic unit, or biozone, is a geological rock layer that is defined by a single index fossil or a fossil assemblage. A biozone can also be used to identify rock layers across distances. The famous White Cliffs of Dover in southwest England can be matched to similar white cliffs in Denmark and Germany. | text | null |
L_0121 | correlation using relative ages | T_1040 | 3. A key bed can be used like an index fossil since a key bed is a distinctive layer of rock that can be recognized across a large area. A volcanic ash unit could be a good key bed. One famous key bed is the clay layer at the boundary between the Cretaceous Period and the Tertiary Period, the time that the dinosaurs went extinct (Figure in asteroids. In 1980, the father-son team of Luis and Walter Alvarez proposed that a huge asteroid struck Earth 66 million years ago and caused the mass extinction. 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_0123 | deep ocean currents | T_1044 | Thermohaline circulation drives deep ocean circulation. Thermo means heat and haline refers to salinity. Dif- ferences in temperature and in salinity change the density of seawater. So thermohaline circulation is the result of density differences in water masses because of their different temperature and salinity. What is the temperature and salinity of very dense water? Lower temperature and higher salinity yield the densest water. When a volume of water is cooled, the molecules move less vigorously, so same number of molecules takes up less space and the water is denser. If salt is added to a volume of water, there are more molecules in the same volume, so the water is denser. | text | null |
L_0123 | deep ocean currents | T_1045 | Changes in temperature and salinity of seawater take place at the surface. Water becomes dense near the poles. Cold polar air cools the water and lowers its temperature, increasing its salinity. Fresh water freezes out of seawater to become sea ice, which also increases the salinity of the remaining water. This very cold, very saline water is very dense and sinks. This sinking is called downwelling. This video lecture discusses the vertical distribution of life in the oceans. Seawater density creates currents, which provide different habitats for different creatures: Click image to the left or use the URL below. URL: Two things then happen. The dense water pushes deeper water out of its way and that water moves along the bottom of the ocean. This deep water mixes with less dense water as it flows. Surface currents move water into the space vacated at the surface where the dense water sank (Figure 1.1). Water also sinks into the deep ocean off of Antarctica. Cold water (blue lines) sinks in the North Atlantic, flows along the bottom of the ocean and upwells in the Pacific or Indian. The water then travels in surface currents (red lines) back to the North Atlantic. Deep water also forms off of Antarctica. | text | null |
L_0123 | deep ocean currents | T_1046 | Since unlimited amounts of water cannot sink to the bottom of the ocean, water must rise from the deep ocean to the surface somewhere. This process is called upwelling (Figure 1.2). Upwelling forces denser water from below to take the place of less dense water at the surface that is pushed away by the wind. Generally, upwelling occurs along the coast when wind blows water strongly away from the shore. This leaves a void that is filled by deep water that rises to the surface. Upwelling is extremely important where it occurs. During its time on the bottom, the cold deep water has collected nutrients that have fallen down through the water column. Upwelling brings those nutrients to the surface. Those nutrients support the growth of plankton and form the base of a rich ecosystem. California, South America, South Africa, and the Arabian Sea all benefit from offshore upwelling. Upwelling also takes place along the Equator between the North and South Equatorial Currents. Winds blow the surface water north and south of the Equator, so deep water undergoes upwelling. The nutrients rise to the surface and support a great deal of life in the equatorial oceans. Click image to the left or use the URL below. URL: | text | null |
L_0124 | determining relative ages | T_1047 | Stenos and Smiths principles are essential for determining the relative ages of rocks and rock layers. In the process of relative dating, scientists do not determine the exact age of a fossil or rock but look at a sequence of rocks to try to decipher the times that an event occurred relative to the other events represented in that sequence. The relative age of a rock then is its age in comparison with other rocks. If you know the relative ages of two rock layers, (1) Do you know which is older and which is younger? (2) Do you know how old the layers are in years? In some cases, it is very tricky to determine the sequence of events that leads to a certain formation. Can you figure out what happened in what order in (Figure 1.1)? Write it down and then check the following paragraphs. The principle of cross-cutting relationships states that a fault or intrusion is younger than the rocks that it cuts through. The fault cuts through all three sedimentary rock layers (A, B, and C) and also the intrusion (D). So the fault must be the youngest feature. The intrusion (D) cuts through the three sedimentary rock layers, so it must be younger than those layers. By the law of superposition, C is the oldest sedimentary rock, B is younger and A is still younger. The full sequence of events is: 1. Layer C formed. 2. Layer B formed. A geologic cross section: Sedimentary rocks (A-C), igneous intrusion (D), fault (E). 3. Layer A formed. 4. After layers A-B-C were present, intrusion D cut across all three. 5. Fault E formed, shifting rocks A through C and intrusion D. 6. Weathering and erosion created a layer of soil on top of layer A. Click image to the left or use the URL below. URL: | text | null |
L_0125 | development of hypotheses | T_1048 | Before we develop some hypotheses, lets find a new question that we want to answer. What we just learned that atmospheric CO2 has been increasing at least since 1958. This leads us to ask this question: Why is atmospheric CO2 increasing? | text | null |
L_0125 | development of hypotheses | T_1049 | We do some background research to find the possible sources of carbon dioxide into the atmosphere. We discover two things: Carbon dioxide is released into the atmosphere by volcanoes when they erupt. Carbon dioxide is released when fossil fuels are burned. A hypothesis is a reasonable explanation to explain a small range of phenomena. A hypothesis is limited in scope, explaining a single event or a fact. A hypothesis must be testable and falsifiable. We must be able to test it and it must be possible to show that it is wrong. From these two facts we can create two hypotheses. We will have multiple working hypotheses. We can test each of these hypotheses. | text | null |
L_0125 | development of hypotheses | T_1050 | Atmospheric CO2 has increased over the past five decades, because the amount of CO2 gas released by volcanoes has increased. | text | null |
L_0125 | development of hypotheses | T_1051 | The increase in atmospheric CO2 is due to the increase in the amount of fossil fuels that are being burned. Usually, testing a hypothesis requires making observations or performing experiments. In this case, we will look into the scientific literature to see if we can support or refute either or both of these hypotheses. Click image to the left or use the URL below. URL: | text | null |
L_0127 | distance between stars | T_1054 | Distances to stars that are relatively close to us can be measured using parallax. Parallax is an apparent shift in position that takes place when the position of the observer changes. To see an example of parallax, try holding your finger about 1 foot (30 cm) in front of your eyes. Now, while focusing on your finger, close one eye and then the other. Alternate back and forth between eyes, and pay attention to how your finger appears to move. The shift in position of your finger is an example of parallax. Now try moving your finger closer to your eyes, and repeat the experiment. Do you notice any difference? The closer your finger is to your eyes, the greater the position changes because of parallax. As Figure 1.1 shows, astronomers use this same principle to measure the distance to stars. Instead of a finger, they focus on a star, and instead of switching back and forth between eyes, they switch between the biggest possible differences in observing position. To do this, an astronomer first looks at the star from one position and notes where the star is relative to more distant stars. Now where will the astronomer go to make an observation the greatest possible distance from the first observation? In six months, after Earth moves from one side of its orbit around the Sun to the other side, the astronomer looks at the star again. This time parallax causes the star to appear in a different position relative to more distant stars. From the size of this shift, astronomers can calculate the distance to the star. | text | null |
L_0127 | distance between stars | T_1055 | Even with the most precise instruments available, parallax is too small to measure the distance to stars that are more than a few hundred light years away. For these more distant stars, astronomers must use more indirect methods of determining distance. Most of these methods involve determining how bright the star they are looking at really is. For example, if the star has properties similar to the Sun, then it should be about as bright as the Sun. The astronomer compares the observed brightness to the expected brightness. | text | null |
L_0128 | distribution of water on earth | T_1056 | Earths oceans contain 97% of the planets water. That leaves just 3% as fresh water, water with low concentrations of salts (Figure 1.1). Most fresh water is trapped as ice in the vast glaciers and ice sheets of Greenland and Antarctica. How is the 3% of fresh water divided into different reservoirs? How much of that water is useful for living creatures? How much for people? A storage location for water such as an ocean, glacier, pond, or even the atmosphere is known as a reservoir. A water molecule may pass through a reservoir very quickly or may remain for much longer. The amount of time a molecule stays in a reservoir is known as its residence time. The distribution of Earths water. Click image to the left or use the URL below. URL: | text | null |
L_0131 | dwarf planets | T_1062 | In 2006, the International Astronomical Union decided that there were too many questions surrounding what could be called a planet, and so refined the definition of a planet. According to the new definition, a planet must: Orbit a star. Be big enough that its own gravity causes it to be shaped as a sphere. Be small enough that it isnt a star itself. Have cleared the area of its orbit of smaller objects. | text | null |
L_0131 | dwarf planets | T_1063 | The dwarf planets of our solar system are exciting proof of how much we are learning about our solar system. With the discovery of many new objects in our solar system, astronomers refined the definition of a dwarf planet in 2006. According to the IAU, a dwarf planet must: Orbit a star. Have enough mass to be nearly spherical. Not have cleared the area around its orbit of smaller objects. Not be a moon. | text | null |
L_0131 | dwarf planets | T_1064 | The reclassification of Pluto to the new category dwarf planet stirred up a great deal of controversy. How the classification of Pluto has evolved is an interesting story in science. From the time it was discovered in 1930 until the early 2000s, Pluto was considered the ninth planet. When astronomers first located Pluto, the telescopes were not as good, so Pluto and its moon, Charon, were seen as one much larger object (Figure 1.1). With better telescopes, astronomers realized that Pluto was much smaller than they had thought. Pluto and its moon, Charon, are actually two objects. Better technology also allowed astronomers to discover many smaller objects like Pluto that orbit the Sun. One of them, Eris, discovered in 2005, is even larger than Pluto. Even when it was considered a planet, Pluto was an oddball. Unlike the other outer planets in the solar system, which are all gas giants, it is small, icy, and rocky. With a diameter of about 2,400 km, it is only about one-fifth the mass of Earths Moon. Plutos orbit is tilted relative to the other planets and is shaped like a long, narrow ellipse. Plutos orbit sometimes even passes inside Neptunes orbit. From what youve read above, do you think Pluto should be called a planet? Why are people hesitant to take away Plutos planetary status? Is Pluto a dwarf planet? Pluto has three moons of its own. The largest, Charon, is big enough that the Pluto-Charon system is sometimes considered to be a double dwarf planet (Figure 1.1). Two smaller moons, Nix and Hydra, were discovered in 2005. But having moons is not enough to make an object a planet. Pluto and the other dwarf planets, besides Ceres, are found orbiting out beyond Neptune. Click image to the left or use the URL below. URL: | text | null |
L_0131 | dwarf planets | T_1065 | Ceres is by far the closest dwarf planet to the Sun; it resides between Mars and Jupiter. Ceres is the largest object in the asteroid belt (Figure 1.2). Before 2006, Ceres was considered the largest of the asteroids, with only about 1.3% of the mass of the Earths Moon. But unlike the asteroids, Ceres has enough mass that its gravity causes it to be shaped like a sphere. Like Pluto, Ceres is rocky. Is Ceres a planet? How does it match the criteria above? Ceres orbits the Sun, is round, and is not a moon. As part of the asteroid belt, its orbit is full of other smaller bodies, so Ceres fails the fourth criterion for being a planet. | text | null |
L_0131 | dwarf planets | T_1066 | Makemake is the third largest and second brightest dwarf planet we have discovered so far (Figure 1.3). With a diameter estimated to be between 1,300 and 1,900 km, it is about three-quarters the size of Pluto. Makemake orbits the Sun in 310 years at a distance between 38.5 to 53 AU. It is thought to be made of methane, ethane, and nitrogen ices. Largest Known Trans-Neptunian Objects. Makemake is named after the deity that created humanity in the mythology of the people of Easter Island. | text | null |
L_0131 | dwarf planets | T_1067 | Eris is the largest known dwarf planet in the solar system it has about 27% more mass than Pluto (Figure 1.3). The object was not discovered until 2003 because it is about three times farther from the Sun than Pluto, and almost 100 times farther from the Sun than Earth is. For a short time Eris was considered the tenth planet in the solar system, but its discovery helped to prompt astronomers to better define planets and dwarf planets in 2006. Eris also has a small moon, Dysnomia, that orbits it once about every 16 days. Astronomers know there may be other dwarf planets in the outer reaches of the solar system. Haumea was made a dwarf planet in 2008, so the total number of dwarf planets is now five. Quaoar, Varuna, and Orcus may be added to the list of dwarf planets in the future. We still have a lot to discover and explore. Click image to the left or use the URL below. URL: | text | null |
L_0132 | early atmosphere and oceans | T_1068 | Earths first atmosphere was made of hydrogen and helium, the gases that were common in this region of the solar system as it was forming. Most of these gases were drawn into the center of the solar nebula to form the Sun. When Earth was new and very small, the solar wind blew off atmospheric gases that collected. If gases did collect, they were vaporized by impacts, especially from the impact that brought about the formation of the Moon. Eventually things started to settle down and gases began to collect. High heat in Earths early days meant that there were constant volcanic eruptions, which released gases from the mantle into the atmosphere (see opening image). Just as today, volcanic outgassing was a source of water vapor, carbon dioxide, small amounts of nitrogen, and other gases. Scientists have calculated that the amount of gas that collected to form the early atmosphere could not have come entirely from volcanic eruptions. Frequent impacts by asteroids and comets brought in gases and ices, including water, carbon dioxide, methane, ammonia, nitrogen, and other volatiles from elsewhere in the solar system (Figure Calculations also show that asteroids and comets cannot be responsible for all of the gases of the early atmosphere, so both impacts and outgassing were needed. | text | null |
L_0132 | early atmosphere and oceans | T_1069 | The second atmosphere, which was the first to stay with the planet, formed from volcanic outgassing and comet ices. This atmosphere had lots of water vapor, carbon dioxide, nitrogen, and methane but almost no oxygen. Why was there so little oxygen? Plants produce oxygen when they photosynthesize but life had not yet begun or had not yet developed photosynthesis. In the early atmosphere, oxygen only appeared when sunlight split water molecules into hydrogen and oxygen and the oxygen accumulated in the atmosphere. Without oxygen, life was restricted to tiny simple organisms. Why is oxygen essential for most life on Earth? 1. Oxygen is needed to make ozone, a molecule made of three oxygen ions, O3 . Ozone collects in the atmospheric ozone layer and blocks harmful ultraviolet radiation from the Sun. Without an ozone layer, life in the early Earth was almost impossible. 2. Animals need oxygen to breathe. No animals would have been able to breathe in Earths early atmosphere. | text | null |
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 |
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