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L_0032 | ecosystems | T_0335 | Food chains are too simple to represent the real world. They dont show all the ways that energy flows through an ecosystem. A more complex diagram is called a food web. You can see an example in Figure 18.8. A food web consists of many overlapping food chains. Can you identify the food chains in the figure? How many food chains include the mouse? | text | null |
L_0032 | ecosystems | T_0336 | Living things need nonliving matter as well as energy. What do you think matter is used for? One thing is to build bodies. They also need it to carry out the processes of life. Any nonliving matter that living things need is called a nutrient. Carbon and nitrogen are examples of nutrients. Unlike energy, matter is recycled in ecosystems. You can see how in Figure 18.9. Decomposers release nutrients when they break down dead organisms. The nutrients are taken up by plants through their roots. The nutrients pass to primary consumers when they eat the plants. The nutrients pass to higher level consumers when they eat lower level consumers. When living things die, the cycle repeats. | text | null |
L_0032 | ecosystems | T_0336 | Living things need nonliving matter as well as energy. What do you think matter is used for? One thing is to build bodies. They also need it to carry out the processes of life. Any nonliving matter that living things need is called a nutrient. Carbon and nitrogen are examples of nutrients. Unlike energy, matter is recycled in ecosystems. You can see how in Figure 18.9. Decomposers release nutrients when they break down dead organisms. The nutrients are taken up by plants through their roots. The nutrients pass to primary consumers when they eat the plants. The nutrients pass to higher level consumers when they eat lower level consumers. When living things die, the cycle repeats. | text | null |
L_0093 | air masses | T_0914 | An air mass is a batch of air that has nearly the same temperature and humidity (Figure 1.1). An air mass acquires these characteristics above an area of land or water known as its source region. When the air mass sits over a region for several days or longer, it picks up the distinct temperature and humidity characteristics of that region. | text | null |
L_0093 | air masses | T_0915 | Air masses form over a large area; they can be 1,600 km (1,000 miles) across and several kilometers thick. Air masses form primarily in high pressure zones, most commonly in polar and tropical regions. Temperate zones are ordinarily too unstable for air masses to form. Instead, air masses move across temperate zones, so the middle latitudes are prone to having interesting weather. The source regions of air masses found around the world. Symbols: (1) origin over a continent (c) or an ocean (m, for maritime); (2) arctic (A), polar (P,) tropical (T), and equatorial (E); (3) properties relative to the ground it moves over: k, for colder, w for warmer. What does an air mass with the symbol cPk mean? The symbol cPk is an air mass with a continental polar source region that is colder than the region it is now moving over. | text | null |
L_0093 | air masses | T_0916 | Air masses are slowly pushed along by high-level winds. When an air mass moves over a new region, it shares its temperature and humidity with that region. So the temperature and humidity of a particular location depends partly on the characteristics of the air mass that sits over it. | text | null |
L_0093 | air masses | T_0917 | Storms arise if the air mass and the region it moves over have different characteristics. For example, when a colder air mass moves over warmer ground, the bottom layer of air is heated. That air rises, forming clouds, rain, and sometimes thunderstorms. How would a moving air mass form an inversion? When a warmer air mass travels over colder ground, the bottom layer of air cools and, because of its high density, is trapped near the ground. | text | null |
L_0093 | air masses | T_0918 | In general, cold air masses tend to flow toward the Equator and warm air masses tend to flow toward the poles. This brings heat to cold areas and cools down areas that are warm. It is one of the many processes that act to balance out the planets temperatures. Click image to the left or use the URL below. URL: | text | null |
L_0100 | biological communities | T_0946 | A population consists of all individuals of a single species that exist together at a given place and time. A species is a single type of organism that can interbreed and produce fertile offspring. All of the populations living together in the same area make up a community. | text | null |
L_0100 | biological communities | T_0947 | An ecosystem is made up of the living organisms in a community and the nonliving things, the physical and chemical factors, that they interact with. The living organisms within an ecosystem are its biotic factors (Figure 1.1). Living things include bacteria, algae, fungi, plants, and animals, including invertebrates, animals without backbones, and vertebrates, animals with backbones. (a) The horsetail Equisetum is a primitive plant. (b) Insects are among the many different types of invertebrates. (c) A giraffe is an example of a vertebrate. Physical and chemical features are abiotic factors. Abiotic factors include resources living organisms need, such as light, oxygen, water, carbon dioxide, good soil, and nitrogen, phosphorous, and other nutrients. Nutrients cycle through different parts of the ecosystem and can enter or leave the ecosystem at many points. Abiotic factors also include environmental features that are not materials or living things, such as living space and the right temperature range. Energy moves through an ecosystem in one direction. Click image to the left or use the URL below. URL: | text | null |
L_0100 | biological communities | T_0948 | Organisms must make a living, just like a lawyer or a ballet dancer. This means that each individual organism must acquire enough food energy to live and reproduce. A species way of making a living is called its niche. An example of a niche is making a living as a top carnivore, an animal that eats other animals, but is not eaten by any other animals (Figure 1.2). Every species fills a niche, and niches are almost always filled in an ecosystem. The top carnivore niche is filled by lions on the savanna. Click image to the left or use the URL below. URL: | text | null |
L_0100 | biological communities | T_0949 | An organisms habitat is where it lives (Figure 1.3). The important characteristics of a habitat include climate, the availability of food, water, and other resources, and other factors, such as weather. | text | null |
L_0101 | blizzards | T_0950 | A blizzard is distinguished by certain conditions: Temperatures below -7 C (20 F); -12 C (10 F) for a severe blizzard. Winds greater than 56 kmh (35 mph); 72 kmh (45 mph) for a severe blizzard. Snow so heavy that visibility is 2/5 km (1/4 mile) or less for at least three hours; near zero visibility for a severe blizzard. | text | null |
L_0101 | blizzards | T_0951 | Blizzards happen across the middle latitudes and toward the poles, usually as part of a mid-latitude cyclone. Bliz- zards are most common in winter, when the jet stream has traveled south and a cold, northern air mass comes into contact with a warmer, semitropical air mass (Figure 1.2). The very strong winds develop because of the pressure gradient between the low-pressure storm and the higher pressure west of the storm. Snow produced by the storm gets caught in the winds and blows nearly horizontally. Blizzards can also produce sleet or freezing rain. A blizzard obscures the Capitol in Wash- ington, DC. Blizzard snows blanket the East Coast of the United States in February 2010. | text | null |
L_0101 | blizzards | T_0951 | Blizzards happen across the middle latitudes and toward the poles, usually as part of a mid-latitude cyclone. Bliz- zards are most common in winter, when the jet stream has traveled south and a cold, northern air mass comes into contact with a warmer, semitropical air mass (Figure 1.2). The very strong winds develop because of the pressure gradient between the low-pressure storm and the higher pressure west of the storm. Snow produced by the storm gets caught in the winds and blows nearly horizontally. Blizzards can also produce sleet or freezing rain. A blizzard obscures the Capitol in Wash- ington, DC. Blizzard snows blanket the East Coast of the United States in February 2010. | text | null |
L_0101 | blizzards | T_0952 | In winter, a continental polar air mass travels down from Canada. As the frigid air travels across one of the Great Lakes, it warms and absorbs moisture. When the air mass reaches the leeward side of the lake, it is very unstable and it drops tremendous amounts of snow. This lake-effect snow falls on the snowiest metropolitan areas in the United States: Buffalo and Rochester, New York (Figure 1.3). Click image to the left or use the URL below. URL: Frigid air travels across the Great Lakes and dumps lake-effect snow on the lee- ward side. | text | null |
L_0102 | branches of earth science | T_0953 | Geology is the study of the Earths solid material and structures and the processes that create them. Some ideas geologists might consider include how rocks and landforms are created or the composition of rocks, minerals, or various landforms. Geologists consider how natural processes create and destroy materials on Earth, and how humans can use Earth materials as resources, among other topics. Geologists study rocks in the field to learn what they can from them. | text | null |
L_0102 | branches of earth science | T_0954 | Oceanography is the study of everything in the ocean environment, which covers about 70% of the Earths surface. Recent technology has allowed people and probes to venture to the deepest parts of the ocean, but much of the ocean remains unexplored. Marine geologists learn about the rocks and geologic processes of the ocean basins. | text | null |
L_0102 | branches of earth science | T_0955 | Meteorology includes the study of weather patterns, clouds, hurricanes, and tornadoes. Using modern technology such as radars and satellites, meteorologists are getting more accurate at forecasting the weather all the time. Climatology is the study of the whole atmosphere, taking a long-range view. Climatologists can help us better understand how and why climate changes (Figure 1.2). Carbon dioxide released into the atmo- sphere is causing the global climate to change. | text | null |
L_0102 | branches of earth science | T_0956 | Environmental scientists study the effects people have on their environment, including the landscape, atmosphere, water, and living things. Climate change is part of climatology or environmental science. | text | null |
L_0102 | branches of earth science | T_0957 | Astronomy is the study of outer space and the physical bodies beyond the Earth. Astronomers use telescopes to see things far beyond what the human eye can see. Astronomers help to design spacecraft that travel into space and send back information about faraway places or satellites (Figure 1.3). The Hubble Space Telescope. 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_0115 | collecting weather data | T_1018 | To make a weather forecast, the conditions of the atmosphere must be known for that location and for the surrounding area. Temperature, air pressure, and other characteristics of the atmosphere must be measured and the data collected. | text | null |
L_0115 | collecting weather data | T_1019 | Thermometers measure temperature. In an old-style mercury thermometer, mercury is placed in a long, very narrow tube with a bulb. Because mercury is temperature sensitive, it expands when temperatures are high and contracts when they are low. A scale on the outside of the thermometer matches up with the air temperature. Some modern thermometers use a coiled strip composed of two kinds of metal, each of which conducts heat differently. As the temperature rises and falls, the coil unfolds or curls up tighter. Other modern thermometers measure infrared radiation or electrical resistance. Modern thermometers usually produce digital data that can be fed directly into a computer. | text | null |
L_0115 | collecting weather data | T_1020 | Meteorologists use barometers to measure air pressure. A barometer may contain water, air, or mercury, but like thermometers, barometers are now mostly digital. A change in barometric pressure indicates that a change in weather is coming. If air pressure rises, a high pressure cell is on the way and clear skies can be expected. If pressure falls, a low pressure cell is coming and will likely bring storm clouds. Barometric pressure data over a larger area can be used to identify pressure systems, fronts, and other weather systems. | text | null |
L_0115 | collecting weather data | T_1021 | Weather stations contain some type of thermometer and barometer. Other instruments measure different characteris- tics of the atmosphere, such as wind speed, wind direction, humidity, and amount of precipitation. These instruments are placed in various locations so that they can check the atmospheric characteristics of that location (Figure 1.1). Weather stations are located on land, the surface of the sea, and in orbit all around the world. According to the World Meteorological Organization, weather information is collected from 15 satellites, 100 stationary buoys, 600 drifting buoys, 3,000 aircraft, 7,300 ships, and some 10,000 land-based stations. | text | null |
L_0115 | collecting weather data | T_1022 | Radiosondes measure atmospheric characteristics, such as temperature, pressure, and humidity as they move through the air. Radiosondes in flight can be tracked to obtain wind speed and direction. Radiosondes use a radio to communicate the data they collect to a computer. Radiosondes are launched from about 800 sites around the globe twice daily to provide a profile of the atmosphere. Radiosondes can be dropped from a balloon or airplane to make measurements as they fall. This is done to monitor storms, for example, since they are dangerous places for airplanes to fly. | text | null |
L_0115 | collecting weather data | T_1023 | Radar stands for Radio Detection and Ranging (Figure 1.2). A transmitter sends out radio waves that bounce off the nearest object and then return to a receiver. Weather radar can sense many characteristics of precipitation: its location, motion, intensity, and the likelihood of future precipitation. Doppler radar can also track how fast the precipitation falls. Radar can outline the structure of a storm and can be used to estimate its possible effects. Radar view of a line of thunderstorms. | text | null |
L_0115 | collecting weather data | T_1024 | Weather satellites have been increasingly important sources of weather data since the first one was launched in 1952. Weather satellites are the best way to monitor large-scale systems, such as storms. Satellites are able to record long-term changes, such as the amount of ice cover over the Arctic Ocean in September each year. Weather satellites may observe all energy from all wavelengths in the electromagnetic spectrum. Visible light images record storms, clouds, fires, and smog. Infrared images record clouds, water and land temperatures, and features of the ocean, such as ocean currents (Figure 1.3). Click image to the left or use the URL below. URL: Infrared data superimposed on a satellite image shows rainfall patterns in Hurricane Ernesto in 2006. | text | null |
L_0126 | development of theories | T_1052 | Scientists seek evidence that supports or refutes a hypothesis. If there is no significant evidence to refute the hypothesis and there is an enormous amount of evidence to support it, the idea is accepted. It may become a theory. A scientific theory is strongly supported by many different lines of evidence. A theory has no major inconsistencies. A theory must be constantly tested and revised. A theory provides a model of reality that is simpler than the phenomenon itself. Scientists can use a theory to offer reliable explanations and make accurate predictions. A theory can be revised or thrown out if conflicting data is discovered. However, a longstanding theory that has lots of evidence to back it up is less likely to be overthrown than a newer theory. But science does not prove anything beyond a shadow of a doubt. Click image to the left or use the URL below. URL: | text | null |
L_0126 | development of theories | T_1053 | Many people think that any idea that is completely accepted in science is a law. In science, a law is something that always applies under the same conditions. If you hold something above the ground and let go it will fall. This phenomenon is recognized by the law of gravity. A law explains a simpler phenomenon or set of phenomena than does a theory. But a theory tells you why something happens and a law only tells you that it happens. Amazingly, scientific laws may have exceptions. Even the law of gravity does not always hold! If water is in an enclosed space between a hillside and a glacier, the weight of the glacier at the bottom of the hill may force the water to flow uphill - against gravity! That doesnt mean that gravity is not a law. A law always applies under the right circumstances. Click image to the left or use the URL below. URL: | text | null |
L_0149 | effect of continental position on climate | T_1125 | When a particular location is near an ocean or large lake, the body of water plays an extremely important role in affecting the regions climate. A maritime climate is strongly influenced by the nearby sea. Temperatures vary a relatively small amount seasonally and daily. For a location to have a true maritime climate, the winds must most frequently come off the sea. A continental climate is more extreme, with greater temperature differences between day and night and between summer and winter. The oceans influence in moderating climate can be seen in the following temperature comparisons. Each of these cities is located at 37o N latitude, within the westerly winds (Figure 1.1). The climate of San Francisco is influenced by the cool California current and offshore upwelling. Wichita has a more extreme continental climate. Virginia Beach, though, is near the Atlantic Ocean. Why is the climate there less influenced by the ocean than is the climate in San Francisco? Hint: Think about the direction the winds are going at that latitude. The weather in San Francisco comes from over the Pacific Ocean while much of the weather in Virginia comes from the continent. How does the ocean influence the climate of these three cities? | text | null |
L_0149 | effect of continental position on climate | T_1126 | The temperature of the water offshore influences the temperature of a coastal location, particularly if the winds come off the sea. The cool waters of the California Current bring cooler temperatures to the California coastal region. Coastal upwelling also brings cold, deep water up to the ocean surface off of California, which contributes to the cool coastal temperatures. Further north, in southern Alaska, the upwelling actually raises the temperature of the surrounding land because the ocean water is much warmer than the land. The important effect of the Gulf Stream on the climate of northern Europe is described in the chapter Water on Earth. | text | null |
L_0152 | effects of air pollution on the environment | T_1132 | All air pollutants cause some damage to living creatures and the environment. Different types of pollutants cause different types of harm. | text | null |
L_0152 | effects of air pollution on the environment | T_1133 | Particulates reduce visibility. In the western United States, people can now ordinarily see only about 100 to 150 kilometers (60 to 90 miles), which is one-half to two-thirds the natural (pre-pollution) range on a clear day. In the East, people can only see about 40 to 60 kilometers (25-35 miles), about one-fifth the distance they could see without any air pollution (Figure 1.1). Particulates reduce the amount of sunshine that reaches the ground, which may reduce photosynthesis. Since particulates form the nucleus for raindrops, snowflakes, or other forms of precipitation, precipitation may increase Smog in New York City. when particulates are high. An increase in particles in the air seems to increase the number of raindrops, but often decreases their size. By reducing sunshine, particulates can also alter air temperature as mentioned above. Imagine how much all of the sources of particulates combine to reduce temperatures. What affect might this have on global warming? | text | null |
L_0152 | effects of air pollution on the environment | T_1134 | Ozone damages some plants. Since ozone effects accumulate, plants that live a long time show the most damage. Some species of trees appear to be the most susceptible. If a forest contains ozone-sensitive trees, they may die out and be replaced by species that are not as easily harmed. This can change an entire ecosystem, because animals and plants may not be able to survive without the habitats created by the native trees. Some crop plants show ozone damage (Figure 1.2). When exposed to ozone, spinach leaves become spotted. Soybeans and other crops have reduced productivity. In developing nations, where getting every last bit of food energy out of the agricultural system is critical, any loss is keenly felt. | text | null |
L_0152 | effects of air pollution on the environment | T_1135 | Oxide air pollutants also damage the environment. NO2 is a toxic, orange-brown colored gas that gives air a distinctive orange color and an unpleasant odor. Nitrogen and sulfur-oxides in the atmosphere create acids that fall as acid rain. Lichen get a lot of their nutrients from the air so they may be good indicators of changes in the atmosphere such as increased nitrogen. In Yosemite National Park, this could change the ecosystem of the region and lead to fires and other problems. The spots on this leaf are caused by ozone damage. Click image to the left or use the URL below. URL: | text | null |
L_0160 | evolution plate tectonics and climate change | T_1154 | Scientific theories are sometimes thrown out when the data shows them to be wrong. Before plate tectonics theory was accepted, people thought that fossil organisms had spread around using land bridges. Although a land bridge across the Atlantic seemed a bit far-fetched, there was no better idea. Most scientists were relieved when they could toss that theory out. But some theories account for so many phenomena and are so broadly supported by so many lines of evidence that they are unlikely ever to be disproved. Additional scientific evidence may reveal problems and scientists may need to modify the theories. But there is so much evidence to support them and nothing major to refute them that they have become essential to their fields of science. | text | null |
L_0160 | evolution plate tectonics and climate change | T_1155 | Darwins theory of evolution has been under attack ever since Darwin proposed it. But nearly all biologists accept the theory and recognize that everything they learn about life on Earth supports the theory. Evolution is seen in the fossil record, in the developmental paths of organisms, in the geographic distribution of organisms, and in the genetic codes of living organisms. Evolution has a mechanism, called natural selection. People often refer to natural selection as the survival of the fittest. With natural selection, the organism that is best adapted to its environment will be most likely to survive and produce offspring, thus spreading its genes to the next generation. The theory of evolution maintains that modern humans evolved from ape-like ancestors. | text | null |
L_0160 | evolution plate tectonics and climate change | T_1156 | The theory of plate tectonics is the most important theory in much of earth science. Plate tectonics explains why much geological activity happens where it does, why many natural resources are found where they are, and can be used to determine what was happening long ago in Earths history. The theory of plate tectonics will be explored in detail in later concepts. | text | null |
L_0160 | evolution plate tectonics and climate change | T_1157 | The theory of climate change is a much newer theory than the previous two. We know that average global tempera- tures are rising. We even know why: Carbon dioxide is released into the atmosphere when fossil fuels are burned. Carbon dioxide is a greenhouse gas. In the atmosphere, greenhouse gases trap heat. This is like putting an extra blanket over Earth. Since more heat is being trapped, global temperature is rising. There is very little information that contradicts the theory that climate is changing due in large part to human activities. Unless some major discrepancy is discovered about how the atmosphere works, the theory is very likely to stand. So far, the evidence that is being collected supports the idea and global warming can be used to predict future events, which are already taking place. This idea will be explored in detail in later concepts. | text | null |
L_0164 | extinction and radiation of life | T_1167 | Most of the species that have lived have also gone extinct. There are two ways to go extinct: besides the obvious way of dying out completely, a species goes extinct if it evolves into a different species. Extinction is a normal part of Earths history. But sometimes large numbers of species go extinct in a short amount of time. This is a mass extinction. The causes of different mass extinctions are different: collisions with comets or asteroids, massive volcanic eruptions, or rapidly changing climate are all possible causes of some of these disasters (Figure 1.1). | text | null |
L_0164 | extinction and radiation of life | T_1168 | After a mass extinction, many habitats are no longer inhabited by organisms because they have gone extinct. With new habitats available, some species will adapt to the new environments. Evolutionary processes act rapidly during An extinct Tyrannosaurus rex. This fossil resembles a living organism. these times and many new species evolve to fill those available habitats. The process in which many new species evolve in a short period of time to fill available niches is called adaptive radiation. At the end of this period of rapid evolution the life forms do not look much like the ones that were around before the mass extinction. For example, after the extinction of the dinosaurs, mammals underwent adaptive radiation and became the dominant life form. | text | null |
L_0168 | flow of matter in ecosystems | T_1184 | The flow of matter in an ecosystem is not like energy flow. Matter enters an ecosystem at any level and leaves at any level. Matter cycles freely between trophic levels and between the ecosystem and the physical environment (Figure | text | null |
L_0168 | flow of matter in ecosystems | T_1185 | Nutrients are ions that are crucial to the growth of living organisms. Nutrients such as nitrogen and phosphorous are important for plant cell growth. Animals use silica and calcium to build shells and skeletons. Cells need nitrates and phosphates to create proteins and other biochemicals. From nutrients, organisms make tissues and complex molecules such as carbohydrates, lipids, proteins, and nucleic acids. What are the sources of nutrients in an ecosystem? Rocks and minerals break down to release nutrients. Some enter the soil and are taken up by plants. Nutrients can be brought in from other regions, carried by wind or water. When one organism eats another organism, it receives all of its nutrients. Nutrients can also cycle out of an ecosystem. Decaying leaves may be transported out of an ecosystem by a stream. Wind or water carries nutrients out of an ecosystem. Nutrients cycle through ocean food webs. Decomposers play a key role in making nutrients available to organisms. Decomposers break down dead organisms into nutrients and carbon dioxide, which they respire into the air. If dead tissue would remain as it is, eventually nutrients would run out. Without decomposers, life on Earth would have died out long ago. | text | null |
L_0182 | global wind belts | T_1233 | Global winds blow in belts encircling the planet. Notice that the locations of these wind belts correlate with the atmospheric circulation cells. Air blowing at the base of the circulation cells, from high pressure to low pressure, creates the global wind belts. The global wind belts are enormous and the winds are relatively steady (Figure 1.1). | text | null |
L_0182 | global wind belts | T_1234 | Lets look at the global wind belts in the Northern Hemisphere. In the Hadley cell air should move north to south, but it is deflected to the right by Coriolis. So the air blows from northeast to the southwest. This belt is the trade winds, so called because at the time of sailing ships they were good for trade. In the Ferrel cell air should move south to north, but the winds actually blow from the southwest. This belt is the westerly winds or westerlies. In the Polar cell, the winds travel from the northeast and are called the polar easterlies. The wind belts are named for the directions from which the winds come. The westerly winds, for example, blow from west to east. These names hold for the winds in the wind belts of the Southern Hemisphere as well. Click image to the left or use the URL below. URL: | text | null |
L_0182 | global wind belts | T_1235 | The high and low pressure areas created by the six atmospheric circulation cells also determine in a general way the amount of precipitation a region receives. Rain is common in low pressure regions due to rising air. Air sinking in high pressure areas causes evaporation; these regions are usually dry. These features have a great deal of influence on climate. | text | null |
L_0182 | global wind belts | T_1236 | The polar front is the junction between the Ferrell and Polar cells. At this low pressure zone, relatively warm, moist air of the Ferrell Cell runs into relatively cold, dry air of the Polar cell. The weather where these two meet is extremely variable, typical of much of North America and Europe. | text | null |
L_0182 | global wind belts | T_1237 | The polar jet stream is found high up in the atmosphere where the two cells come together. A jet stream is a fast- flowing river of air at the boundary between the troposphere and the stratosphere. Jet streams form where there is a large temperature difference between two air masses. This explains why the polar jet stream is the worlds most powerful (Figure 1.2). A cross section of the atmosphere with major circulation cells and jet streams. The polar jet stream is the site of extremely turbulent weather. Jet streams move seasonally just as the angle of the Sun in the sky moves north and south. The polar jet stream, known as the jet stream, moves south in the winter and north in the summer between about 30 N and 50 to 75 N. Click image to the left or use the URL below. URL: | text | null |
L_0193 | history of cenozoic life | T_1263 | The extinction of so many species at the end of the Mesozoic again left many niches available to be filled. Although we call the Cenozoic the age of mammals, birds are more common and more diverse. Early in the era, terrestrial crocodiles lumbered around along with large, primitive mammals and prehistoric birds. | text | null |
L_0193 | history of cenozoic life | T_1264 | Their adaptations have allowed mammals to spread to even more environments than reptiles. The success of mammals is due to several of their unique traits. Mammals are endothermic and have fur, hair, or blubber for warmth. Mammals can swim, fly, and live in nearly all terrestrial environments. Mammals initially filled the forests that covered many early Cenozoic lands. Over time, the forests gave way to grasslands, which created more niches for mammals to fill. | text | null |
L_0193 | history of cenozoic life | T_1265 | As climate cooled during the ice ages, large mammals were able to stand the cold weather, so many interesting megafauna developed. These included giant sloths, saber-toothed cats, wooly mammoths, giant condors, and many other animals that are now extinct (Figure 1.1). Many of the organisms that made up the Pleistocene megafauna went extinct as conditions warmed. Some may have been driven to extinction by human activities. Imagine a vast grassy plain covered with herds of elephants, bison and camels stretching as far as the eye can see. Lions, tigers, wolves and later, humans, hunt the herds on their summer migration. This was the San Francisco Bay Area at the close of the last Ice Age. Click image to the left or use the URL below. URL: | text | null |
L_0194 | history of mesozoic life | T_1266 | With most niches available after the mass extinction, a great diversity of organisms evolved. Mostly these niches were filled with reptiles. Climate alternated between cool, warm, and tropical, but overall the planet was much warmer than today. These conditions were good for reptiles. Surprisingly, there was more oxygen in the Mesozoic atmosphere than there is today. | text | null |
L_0194 | history of mesozoic life | T_1267 | Tiny phytoplankton arose to become the base of the marine food web. At the beginning of the Mesozoic, Pangaea began to break apart, so more beaches and continental shelf areas were available for colonization by new species of marine organisms. Marine reptiles colonized the seas and diversified. Some became huge, filling the niches that are filled by large marine mammals today. | text | null |
L_0194 | history of mesozoic life | T_1268 | On land, seed plants and trees diversified and spread widely. Ferns were common at the time of the dinosaurs (Figure | text | null |
L_0194 | history of mesozoic life | T_1269 | Of course the most famous Mesozoic reptiles were the dinosaurs (Figure 1.2). Dinosaurs reigned for 160 million years and had tremendous numbers and diversity. Species of dinosaurs filled all the niches that are currently filled by mammals. Dinosaurs were plant eaters, meat eaters, bipedal, quadrupedal, endothermic (warm-blooded), exothermic (cold-blooded), enormous, small, and some could swim or fly. Scientists now think that some dinosaurs were endotherms (warm-blooded) due to the evidence that has been collected over the decades. There are still some scientists who do not agree, but the amount of evidence makes it likely. Some dinosaurs lived in polar regions where animals that needed sunlight for warmth could not survive in winter. Dinosaurs bones had canals, similar to those of birds, indicating that they grew fast and were very active. Fast growth usually indicates an active metabolism typical of endotherms. Dinosaurs had erect posture and large brains, both correlated with endothermy. The earliest known fossil of a flowering plant is this 125 million year old Creta- ceous fossil. | text | null |
L_0194 | history of mesozoic life | T_1270 | Mammals appeared near the end of the Triassic, but the Mesozoic is known as the age of the reptiles. In a great advance over amphibians, which must live near water, reptiles developed adaptations for living away from water. Their thick skin keeps them from drying out, and the evolution of the amniote egg allowed them to lay their eggs on dry land. The amniote egg has a shell and contains all the nutrients and water required for the developing embryo (Figure 1.3). | text | null |
L_0194 | history of mesozoic life | T_1271 | Between the Mesozoic and the Cenozoic, 65 million years ago, about 50% of all animal species, including the dinosaurs, became extinct. Although there are other hypotheses, most scientists think that this mass extinction took place when a giant meteorite struck Earth with 2 million times the energy of the most powerful nuclear weapon (Figure 1.4). The impact kicked up a massive dust cloud, and when the particles rained back onto the surface they heated the atmosphere until it became as hot as a kitchen oven. Animals roasted. Dust that remained in the atmosphere blocked sunlight for a year or more, causing a deep freeze and temporarily ending photosynthesis. Sulfur from the impact mixed with water in the atmosphere to form acid rain, which dissolved the shells of the tiny marine plankton that form the base of the food chain. With little food being produced by land plants and plankton, animals starved. Carbon dioxide was also released from the impact and eventually caused global warming. Life forms could not survive the dramatic temperature swings. You may be surprised to know that dinosaurs in one form survived the mass extinctions and live all over the world today. Birds evolved from theropod dinosaurs, and these creatures not only survived the asteroid impact and its aftermath, but they have also diversified into some of the most fantastic creatures we know (Figure 1.5). | text | null |
L_0195 | history of paleozoic life | T_1272 | The Paleozoic saw the evolution a tremendous diversity of life throughout the seas and onto land. | text | null |
L_0195 | history of paleozoic life | T_1273 | The Cambrian began with the most rapid and far-reaching evolution of life forms ever in Earths history. Evolving to inhabit so many different habitats resulted in a tremendous diversification of life forms. Shallow seas covered the lands, so every major marine organism group, including nearly all invertebrate animal phyla, evolved during this time. With the evolution of hard body parts, fossils are much more abundant and better preserved from this period than from the Precambrian. The Burgess shale formation in the Rocky Mountains of British Columbia, Canada, contains an amazing diversity of middle Cambrian life forms, from about 505 million years ago. Paleontologists do not agree on whether the Burgess shale fossils can all be classified into modern groups of organisms or whether many represent lines that have gone completely extinct. | text | null |
L_0195 | history of paleozoic life | T_1274 | Throughout the Paleozoic, seas transgressed and regressed. When continental areas were covered with shallow seas, the number and diversity of marine organisms increased. During regressions the number shrank. Arthropods, fish, amphibians and reptiles all originated in the Paleozoic. Simple plants began to colonize the land during the Ordovician, but land plants really flourished when seeds evolved during the Carboniferous (Figure 1.2). The abundant swamps became the coal and petroleum deposits that are the source of much of our fossil fuels today. During the later part of the Paleozoic, land animals and insects greatly increased in numbers and diversity. A modern rainforest has many seed- bearing plants that are similar to those that were common during the Carbonifer- ous. | text | null |
L_0195 | history of paleozoic life | T_1274 | Throughout the Paleozoic, seas transgressed and regressed. When continental areas were covered with shallow seas, the number and diversity of marine organisms increased. During regressions the number shrank. Arthropods, fish, amphibians and reptiles all originated in the Paleozoic. Simple plants began to colonize the land during the Ordovician, but land plants really flourished when seeds evolved during the Carboniferous (Figure 1.2). The abundant swamps became the coal and petroleum deposits that are the source of much of our fossil fuels today. During the later part of the Paleozoic, land animals and insects greatly increased in numbers and diversity. A modern rainforest has many seed- bearing plants that are similar to those that were common during the Carbonifer- ous. | text | null |
L_0195 | history of paleozoic life | T_1275 | Large extinction events separate the periods of the Paleozoic. After extinctions, new life forms evolved (Figure ). For example, after the extinction at the end of the Ordovician, fish and the first tetrapod animals appeared. Tetrapods are four legged vertebrates, but the earliest ones did not leave shallow, brackish water. | text | null |
L_0195 | history of paleozoic life | T_1276 | The largest mass extinction in Earths history occurred at the end of the Permian period, about 250 million years ago. In this catastrophe, it is estimated that more than 95% of marine species on Earth went extinct. Marine species with calcium carbonate shells and skeletons suffered worst. About 70% of terrestrial vertebrate species (land animals) suffered the same fate. This was the only known mass extinction of insects. This mass extinction appears to have taken place in three pulses, with three separate causes. Gradual environmental change, an asteroid impact, intense volcanism, or changes in the composition of the atmosphere may all have played a role. Click image to the left or use the URL below. URL: | text | null |
L_0200 | hurricanes | T_1292 | Hurricanes called typhoons in the Pacific are also cyclones. They are cyclones that form in the tropics and so they are also called tropical cyclones. By any name, they are the most damaging storms on Earth. | text | null |
L_0200 | hurricanes | T_1293 | Hurricanes arise in the tropical latitudes (between 10o and 25o N) in summer and autumn when sea surface temper- ature are 28o C (82o F) or higher. The warm seas create a large humid air mass. The warm air rises and forms a low pressure cell, known as a tropical depression. Thunderstorms materialize around the tropical depression. If the temperature reaches or exceeds 28o C (82o F), the air begins to rotate around the low pressure (counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere). As the air rises, water vapor condenses, releasing energy from latent heat. If wind shear is low, the storm builds into a hurricane within two to three days. Hurricanes are huge and produce high winds. The exception is the relatively calm eye of the storm, where air is rising upward. Rainfall can be as high as 2.5 cm (1") per hour, resulting in about 20 billion metric tons of water released daily in a hurricane. The release of latent heat generates enormous amounts of energy, nearly the total annual electrical power consumption of the United States from one storm. Hurricanes can also generate tornadoes. A cross-sectional view of a hurricane. Hurricanes move with the prevailing winds. In the Northern Hemisphere, they originate in the trade winds and move to the west. When they reach the latitude of the westerlies, they switch direction and travel toward the north or northeast. Hurricanes may cover 800 km (500 miles) in one day. Click image to the left or use the URL below. URL: | text | null |
L_0200 | hurricanes | T_1294 | Hurricanes are assigned to categories based on their wind speed. The categories are listed on the Saffir-Simpson hurricane scale (Table 1.1). Category 1 (weak) Kph 119-153 Mph 74-95 2 (moderate) 154-177 96-110 3 (strong) 178-209 111-130 Estimated Damage Above normal; no real damage to structures Some roofing, door, and window damage, consid- erable damage to vegeta- tion, mobile homes, and piers Some buildings damaged; mobile homes destroyed Category 4 (very strong) Kph 210-251 Mph 131-156 5 (devastating) >251 >156 Estimated Damage Complete roof failure on small residences; major erosion of beach areas; major damage to lower floors of structures near shore Complete roof failure on many residences and in- dustrial buildings; some complete building failures | text | null |
L_0200 | hurricanes | T_1295 | Damage from hurricanes comes from the high winds, rainfall, and storm surge. Storm surge occurs as the storms low pressure center comes onto land, causing the sea level to rise unusually high. A storm surge is often made worse by the hurricanes high winds blowing seawater across the ocean onto the shoreline. Flooding can be devastating, especially along low-lying coastlines such as the Atlantic and Gulf Coasts. Hurricane Camille in 1969 had a 7.3 m (24 foot) storm surge that traveled 125 miles (200 km) inland. | text | null |
L_0200 | hurricanes | T_1296 | Hurricanes typically last for 5 to 10 days. The winds push them to the northwest and then to the northeast. Eventually a hurricane will end up over cooler water or land. At that time the hurricanes latent heat source shut downs and the storm weakens. When a hurricane disintegrates, it is replaced with intense rains and tornadoes. There are about 100 hurricanes around the world each year, plus many smaller tropical storms and tropical depres- sions. As people develop coastal regions, property damage from storms continues to rise. However, scientists are becoming better at predicting the paths of these storms and fatalities are decreasing. There is, however, one major exception to the previous statement: Hurricane Katrina. | text | null |
L_0200 | hurricanes | T_1297 | The 2005 Atlantic hurricane season was the longest, costliest, and deadliest hurricane season so far. Total damage from all the storms together was estimated at more than $128 billion, with more than 2,280 deaths. Hurricane Katrina was both the most destructive hurricane and the most costly (Figure 1.2). | text | null |
L_0219 | local winds | T_1372 | Local winds result from air moving between small low and high pressure systems. High and low pressure cells are created by a variety of conditions. Some local winds have very important effects on the weather and climate of some regions. | text | null |
L_0219 | local winds | T_1373 | Since water has a very high specific heat, it maintains its temperature well. So water heats and cools more slowly than land. If there is a large temperature difference between the surface of the sea (or a large lake) and the land next to it, high and low pressure regions form. This creates local winds. Sea breezes blow from the cooler ocean over the warmer land in summer. Where is the high pressure zone and where is the low pressure zone (Figure 1.1)? Sea breezes blow at about 10 to 20 km (6 to 12 miles) per hour and lower air temperature much as 5 to 10o C (9 to 18o F). Land breezes blow from the land to the sea in winter. Where is the high pressure zone and where is the low pressure zone? Some warmer air from the ocean rises and then sinks on land, causing the temperature over the land to become warmer. How do sea and land breezes moderate coastal climates? Land and sea breezes create the pleasant climate for which Southern California is known. The effect of land and sea breezes are felt only about 50 to 100 km (30 to 60 miles) inland. This same cooling and warming effect occurs to a smaller degree during day and night, because land warms and cools faster than the ocean. | text | null |
L_0219 | local winds | T_1374 | Monsoon winds are larger scale versions of land and sea breezes; they blow from the sea onto the land in summer and from the land onto the sea in winter. Monsoon winds occur where very hot summer lands are next to the sea. Thunderstorms are common during monsoons (Figure 1.2). In the southwestern United States rela- tively cool moist air sucked in from the Gulf of Mexico and the Gulf of California meets air that has been heated by scorch- ing desert temperatures. The most important monsoon in the world occurs each year over the Indian subcontinent. More than two billion residents of India and southeastern Asia depend on monsoon rains for their drinking and irrigation water. Back in the days of sailing ships, seasonal shifts in the monsoon winds carried goods back and forth between India and Africa. | text | null |
L_0219 | local winds | T_1375 | Temperature differences between mountains and valleys create mountain and valley breezes. During the day, air on mountain slopes is heated more than air at the same elevation over an adjacent valley. As the day progresses, warm air rises and draws the cool air up from the valley, creating a valley breeze. At night the mountain slopes cool more quickly than the nearby valley, which causes a mountain breeze to flow downhill. | text | null |
L_0219 | local winds | T_1376 | Katabatic winds move up and down slopes, but they are stronger mountain and valley breezes. Katabatic winds form over a high land area, like a high plateau. The plateau is usually surrounded on almost all sides by mountains. In winter, the plateau grows cold. The air above the plateau grows cold and sinks down from the plateau through gaps in the mountains. Wind speeds depend on the difference in air pressure over the plateau and over the surroundings. Katabatic winds form over many continental areas. Extremely cold katabatic winds blow over Antarctica and Greenland. | text | null |
L_0219 | local winds | T_1377 | Chinook winds (or Foehn winds) develop when air is forced up over a mountain range. This takes place, for example, when the westerly winds bring air from the Pacific Ocean over the Sierra Nevada Mountains in California. As the relatively warm, moist air rises over the windward side of the mountains, it cools and contracts. If the air is humid, it may form clouds and drop rain or snow. When the air sinks on the leeward side of the mountains, it forms a high pressure zone. The windward side of a mountain range is the side that receives the wind; the leeward side is the side where air sinks. The descending air warms and creates strong, dry winds. Chinook winds can raise temperatures more than 20o C (36o F) in an hour and they rapidly decrease humidity. Snow on the leeward side of the mountain melts quickly. If precipitation falls as the air rises over the mountains, the air will be dry as it sinks on the leeward size. This dry, sinking air causes a rainshadow effect (Figure 1.3), which creates many of the worlds deserts. | text | null |
L_0219 | local winds | T_1378 | Santa Ana winds are created in the late fall and winter when the Great Basin east of the Sierra Nevada cools, creating a high pressure zone. The high pressure forces winds downhill and in a clockwise direction (because of Coriolis). The air pressure rises, so temperature rises and humidity falls. The winds blow across the Southwestern deserts and then race downhill and westward toward the ocean. Air is forced through canyons cutting the San Gabriel and San Bernardino mountains. (Figure 1.4). The winds are especially fast through Santa Ana Canyon, for which they are named. Santa Ana winds blow dust and smoke westward over the Pacific from Southern California. The Santa Ana winds often arrive at the end of Californias long summer drought season. The hot, dry winds dry out the landscape even more. If a fire starts, it can spread quickly, causing large-scale devastation (Figure 1.5). In October 2007, Santa Ana winds fueled many fires that together burned 426,000 acres of wild land and more than 1,500 homes in Southern California. | text | null |
L_0219 | local winds | T_1378 | Santa Ana winds are created in the late fall and winter when the Great Basin east of the Sierra Nevada cools, creating a high pressure zone. The high pressure forces winds downhill and in a clockwise direction (because of Coriolis). The air pressure rises, so temperature rises and humidity falls. The winds blow across the Southwestern deserts and then race downhill and westward toward the ocean. Air is forced through canyons cutting the San Gabriel and San Bernardino mountains. (Figure 1.4). The winds are especially fast through Santa Ana Canyon, for which they are named. Santa Ana winds blow dust and smoke westward over the Pacific from Southern California. The Santa Ana winds often arrive at the end of Californias long summer drought season. The hot, dry winds dry out the landscape even more. If a fire starts, it can spread quickly, causing large-scale devastation (Figure 1.5). In October 2007, Santa Ana winds fueled many fires that together burned 426,000 acres of wild land and more than 1,500 homes in Southern California. | text | null |
L_0219 | local winds | T_1379 | High summer temperatures on the desert create high winds, which are often associated with monsoon storms. Desert winds pick up dust because there is not as much vegetation to hold down the dirt and sand. (Figure 1.6). A haboob forms in the downdrafts on the front of a thunderstorm. Dust devils, also called whirlwinds, form as the ground becomes so hot that the air above it heats and rises. Air flows into the low pressure and begins to spin. Dust devils are small and short-lived, but they may cause damage. | text | null |
L_0239 | mid latitude cyclones | T_1436 | Cyclones can be the most intense storms on Earth. A cyclone is a system of winds rotating counterclockwise in the Northern Hemisphere around a low pressure center. The swirling air rises and cools, creating clouds and precipitation. Mid-latitude cyclones form at the polar front when the temperature difference between two air masses is large. These air masses blow past each other in opposite directions. Coriolis effect deflects winds to the right in the Northern Hemisphere, causing the winds to strike the polar front at an angle. Warm and cold fronts form next to each other. Most winter storms in the middle latitudes, including most of the United States and Europe, are caused by mid-latitude cyclones (Figure 1.1). The warm air at the cold front rises and creates a low pressure cell. Winds rush into the low pressure and create a rising column of air. The air twists, rotating counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Since the rising air is moist, rain or snow falls. Mid-latitude cyclones form in winter in the mid-latitudes and move eastward with the westerly winds. These two- to five-day storms can reach 1,000 to 2,500 km (625 to 1,600 miles) in diameter and produce winds up to 125 km (75 miles) per hour. | text | null |
L_0239 | mid latitude cyclones | T_1437 | Mid-latitude cyclones are especially fierce in the mid-Atlantic and New England states, where they are called noreasters because they come from the northeast. About 30 noreasters strike the region each year. (Figure A hypothetical mid-latitude cyclone affect- ing the United Kingdom. The arrows point the wind direction and its relative temper- ature; L is the low pressure area. Notice the warm, cold, and occluded fronts. The 1993 Storm of the Century was a noreaster that covered the entire eastern seaboard of the United States. | text | null |
L_0239 | mid latitude cyclones | T_1437 | Mid-latitude cyclones are especially fierce in the mid-Atlantic and New England states, where they are called noreasters because they come from the northeast. About 30 noreasters strike the region each year. (Figure A hypothetical mid-latitude cyclone affect- ing the United Kingdom. The arrows point the wind direction and its relative temper- ature; L is the low pressure area. Notice the warm, cold, and occluded fronts. The 1993 Storm of the Century was a noreaster that covered the entire eastern seaboard of the United States. | text | null |
L_0245 | modern biodiversity | T_1471 | There are more than 1 million species of plants and animals known to be currently alive on Earth (Figure 1.1) and many millions more that have not been discovered yet. The tremendous variety of creatures is due to the tremendous numbers of habitats that organisms have evolved to fill. | text | null |
L_0245 | modern biodiversity | T_1472 | Many adaptations protect organisms from the external environment (Figure 1.2). Other adaptations help an organism move or gather food. Reindeer have sponge-like hoofs that help them walk on snowy ground without slipping and falling. Hummingbirds have long, thin beaks that help them drink nectar from flowers. Organisms have special features that help them avoid being eaten. When a herd of zebras run away from lions, the zebras dark stripes confuse the predators so that they have difficulty focusing on just one zebra during the chase. Some plants have poisonous or foul-tasting substances in them that keep animals from eating them. Their brightly colored flowers serve as a warning. There is an amazing diversity of organisms on Earth. How do the organisms in this picture each make their living? Cacti have thick, water- retaining bodies that help them conserve water. Poison dart frogs have toxins in their skin. Their bright colors warn potential predators not to take a bite! Thousands of northern elephant seals some weighing up to 4,500 pounds make an annual migration to breed each winter at Ao Nuevo State Reserve in California. Marine biologists are using high-tech tools to explore the secrets of these amazing creatures. Click image to the left or use the URL below. URL: | text | null |
L_0245 | modern biodiversity | T_1472 | Many adaptations protect organisms from the external environment (Figure 1.2). Other adaptations help an organism move or gather food. Reindeer have sponge-like hoofs that help them walk on snowy ground without slipping and falling. Hummingbirds have long, thin beaks that help them drink nectar from flowers. Organisms have special features that help them avoid being eaten. When a herd of zebras run away from lions, the zebras dark stripes confuse the predators so that they have difficulty focusing on just one zebra during the chase. Some plants have poisonous or foul-tasting substances in them that keep animals from eating them. Their brightly colored flowers serve as a warning. There is an amazing diversity of organisms on Earth. How do the organisms in this picture each make their living? Cacti have thick, water- retaining bodies that help them conserve water. Poison dart frogs have toxins in their skin. Their bright colors warn potential predators not to take a bite! Thousands of northern elephant seals some weighing up to 4,500 pounds make an annual migration to breed each winter at Ao Nuevo State Reserve in California. Marine biologists are using high-tech tools to explore the secrets of these amazing creatures. Click image to the left or use the URL below. URL: | text | null |
L_0245 | modern biodiversity | T_1472 | Many adaptations protect organisms from the external environment (Figure 1.2). Other adaptations help an organism move or gather food. Reindeer have sponge-like hoofs that help them walk on snowy ground without slipping and falling. Hummingbirds have long, thin beaks that help them drink nectar from flowers. Organisms have special features that help them avoid being eaten. When a herd of zebras run away from lions, the zebras dark stripes confuse the predators so that they have difficulty focusing on just one zebra during the chase. Some plants have poisonous or foul-tasting substances in them that keep animals from eating them. Their brightly colored flowers serve as a warning. There is an amazing diversity of organisms on Earth. How do the organisms in this picture each make their living? Cacti have thick, water- retaining bodies that help them conserve water. Poison dart frogs have toxins in their skin. Their bright colors warn potential predators not to take a bite! Thousands of northern elephant seals some weighing up to 4,500 pounds make an annual migration to breed each winter at Ao Nuevo State Reserve in California. Marine biologists are using high-tech tools to explore the secrets of these amazing creatures. Click image to the left or use the URL below. URL: | text | null |
L_0254 | observations and experiments | T_1499 | If we were doing a scientific investigation we need to gather the information to test the hypotheses ourselves. We would do this by making observations or running experiments. | text | null |
L_0254 | observations and experiments | T_1500 | Observations of Earths surface may be made from the land surface or from space. Many important observations are made by orbiting satellites, which have a birds eye view of how the planet is changing (for example, see Figure Often, observation is used to collect data when it is not possible for practical or ethical reasons to perform experi- ments. Scientists may send devices to make observations for them when it is too dangerous or impractical for them to make the observations directly. They may use microscopes to explore tiny objects or telescopes to learn about the universe (see Figure 1.2). Artists concept of the Juno orbiter circling Jupiter. The mission is ongoing. | text | null |
L_0254 | observations and experiments | T_1500 | Observations of Earths surface may be made from the land surface or from space. Many important observations are made by orbiting satellites, which have a birds eye view of how the planet is changing (for example, see Figure Often, observation is used to collect data when it is not possible for practical or ethical reasons to perform experi- ments. Scientists may send devices to make observations for them when it is too dangerous or impractical for them to make the observations directly. They may use microscopes to explore tiny objects or telescopes to learn about the universe (see Figure 1.2). Artists concept of the Juno orbiter circling Jupiter. The mission is ongoing. | text | null |
L_0254 | observations and experiments | T_1501 | Answering some questions requires experiments. An experiment is a test that may be performed in the field or in a laboratory. An experiment must always done under controlled conditions. The goal of an experiment is to verify or falsify a hypothesis. In an experiment, it is important to change only one factor. All other factors must be kept the same. Independent variable: The factor that will be manipulated. Dependent variable: The factors that depend on the independent variable. An experiment must have a control group. The control group is not subjected to the independent variable. For example, if you want to test if Vitamin C prevents colds, you must divide your sample group up so that some receive Vitamin C and some do not. Those who do not receive the Vitamin C are the control group. | text | null |
L_0254 | observations and experiments | T_1502 | Scientists often make many measurements during experiments. As in just about every human endeavor, errors are unavoidable. In a scientific experiment, this is called experimental error. Systematic errors are part of the experimental setup, so that the numbers are always skewed in one direction. For example, a scale may always measure one-half of an ounce high. Random errors occur because a measurement is not made precisely. For example, a stopwatch may be stopped too soon or too late. To correct for this, many measurements are taken and then averaged. Experiments always have a margin of error associated with them. In an experiment, if a result is inconsistent with the results from other samples and many tests have been done, it is likely that a mistake was made in that experiment. The inconsistent data point can be thrown out. Click image to the left or use the URL below. URL: | text | null |
L_0275 | predicting weather | T_1577 | The most accurate weather forecasts are made by advanced computers, with analysis and interpretation added by experienced meteorologists. These computers have up-to-date mathematical models that can use much more data and make many more calculations than would ever be possible by scientists working with just maps and calculators. Meteorologists can use these results to give much more accurate weather forecasts and climate predictions. In Numerical Weather Prediction (NWP), atmospheric data from many sources are plugged into supercomputers running complex mathematical models (Figure 1.1). The models then calculate what will happen over time at various altitudes for a grid of evenly spaced locations. The grid points are usually between 10 and 200 kilometers apart. Using the results calculated by the model, the program projects weather further into the future. It then uses these results to project the weather still further into the future, as far as the meteorologists want to go. Once a forecast is made, it is broadcast by satellites to more than 1,000 sites around the world. NWP produces the most accurate weather forecasts, but as anyone knows, even the best forecasts are not always right. Weather prediction is extremely valuable for reducing property damage and even fatalities. If the proposed track of a hurricane can be predicted, people can try to secure their property and then evacuate (Figure 1.2). A weather forecast using numerical weather prediction. | text | null |
L_0275 | predicting weather | T_1577 | The most accurate weather forecasts are made by advanced computers, with analysis and interpretation added by experienced meteorologists. These computers have up-to-date mathematical models that can use much more data and make many more calculations than would ever be possible by scientists working with just maps and calculators. Meteorologists can use these results to give much more accurate weather forecasts and climate predictions. In Numerical Weather Prediction (NWP), atmospheric data from many sources are plugged into supercomputers running complex mathematical models (Figure 1.1). The models then calculate what will happen over time at various altitudes for a grid of evenly spaced locations. The grid points are usually between 10 and 200 kilometers apart. Using the results calculated by the model, the program projects weather further into the future. It then uses these results to project the weather still further into the future, as far as the meteorologists want to go. Once a forecast is made, it is broadcast by satellites to more than 1,000 sites around the world. NWP produces the most accurate weather forecasts, but as anyone knows, even the best forecasts are not always right. Weather prediction is extremely valuable for reducing property damage and even fatalities. If the proposed track of a hurricane can be predicted, people can try to secure their property and then evacuate (Figure 1.2). A weather forecast using numerical weather prediction. | text | null |
L_0276 | pressure and density of the atmosphere | T_1578 | The atmosphere has different properties at different elevations above sea level, or altitudes. | text | null |
L_0276 | pressure and density of the atmosphere | T_1579 | The air density (the number of molecules in a given volume) decreases with increasing altitude. This is why people who climb tall mountains, such as Mt. Everest, have to set up camp at different elevations to let their bodies get used to the decreased air density (Figure 1.1). Why does air density decrease with altitude? Gravity pulls the gas molecules towards Earths center. The pull of gravity is stronger closer to the center, at sea level. Air is denser at sea level, where the gravitational pull is greater. Click image to the left or use the URL below. URL: | text | null |
L_0276 | pressure and density of the atmosphere | T_1580 | Gases at sea level are also compressed by the weight of the atmosphere above them. The force of the air weighing down over a unit of area is known as its atmospheric pressure, or air pressure. Why are we not crushed? The molecules inside our bodies are pushing outward to compensate. Air pressure is felt from all directions, not just from above. This bottle was closed at an altitude of 3,000 meters where air pressure is lower. When it was brought down to sea level, the higher air pressure caused the bottle to collapse. At higher altitudes the atmospheric pressure is lower and the air is less dense than at lower altitudes. Thats what makes your ears pop when you change altitude. Gas molecules are found inside and outside your ears. When you change altitude quickly, like when an airplane is descending, your inner ear keeps the density of molecules at the original altitude. Eventually the air molecules inside your ear suddenly move through a small tube in your ear to equalize the pressure. This sudden rush of air is felt as a popping sensation. Click image to the left or use the URL below. URL: | text | null |
L_0290 | roles in an ecosystem | T_1631 | There are many different types of ecosystems. Climate conditions determine which ecosystems are found in a particular location. A biome encompasses all of the ecosystems that have similar climate and organisms. Different organisms live in different types of ecosystems because they are adapted to different conditions. Lizards thrive in deserts, but no reptiles are found in any polar ecosystems. Amphibians cant live too far from the water. Large animals generally do better in cold climates than in hot climates. Despite this, every ecosystem has the same general roles that living creatures fill. Its just the organisms that fill those niches that are different. For example, every ecosystem must have some organisms that produce food in the form of chemical energy. These organisms are primarily algae in the oceans, plants on land, and bacteria at hydrothermal vents. | text | null |
L_0290 | roles in an ecosystem | T_1632 | The organisms that produce food are extremely important in every ecosystem. Organisms that produce their own food are called producers. There are two ways of producing food energy: Photosynthesis: plants on land, phytoplankton in the surface ocean, and some other organisms. Chemosynthesis: bacteria at hydrothermal vents. Organisms that use the food energy that was created by producers are named consumers. There are many types of consumers: Herbivores eat producers directly. These animals break down the plant structures to get the materials and energy they need. Carnivores eat animals; they can eat herbivores or other carnivores. Omnivores eat plants and animals as well as fungi, bacteria, and organisms from the other kingdoms. | text | null |
L_0290 | roles in an ecosystem | T_1633 | There are many types of feeding relationships (Figure 1.2) between organisms. A predator is an animal that kills and eats another animal, known as its prey. Scavengers are animals, such as vultures and hyenas, that eat organisms that are already dead. Decomposers break apart dead organisms or the waste material of living organisms, returning the nutrients to the ecosystem. (a) Predator and prey; (b) Scavengers; (c) Bacteria and fungi, acting as decomposers. | text | null |
L_0290 | roles in an ecosystem | T_1634 | Species have different types of relationships with each other. Competition occurs between species that try to use the same resources. When there is too much competition, one species may move or adapt so that it uses slightly different resources. It may live at the tops of trees and eat leaves that are somewhat higher on bushes, for example. If the competition does not end, one species will die out. Each niche can only be inhabited by one species. Some relationships between species are beneficial to at least one of the two interacting species. These relationships are known as symbiosis and there are three types: In mutualism, the relationship benefits both species. Most plant-pollinator relationships are mutually benefi- cial. What does each get from the relationship? In commensalism, one organism benefits and the other is not harmed. In parasitism, the parasite species benefits and the host is harmed. Parasites do not usually kill their hosts because a dead host is no longer useful to the parasite. Humans host parasites, such as the flatworms that cause schistosomiasis. Choose which type of relationship is described by each of the images and captions below (Figure 1.3). Click image to the left or use the URL below. URL: (a) The pollinator gets food; the plants pollen gets caught in the birds feathers so it is spread to far away flowers. (b) The barnacles receive protection and get to move to new locations; the whale is not harmed. (c) These tiny mites are parasitic and consume the insect called a harvestman. Click image to the left or use the URL below. URL: | text | null |
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