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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 |
L_0296 | scientific community | T_1654 | A hypothesis will not be fully accepted unless it is supported by the work of many scientists. Although a study may take place in a single laboratory, a scientist must present her work to the community of scientists in her field. Initially, she may present her data and conclusions at a scientific conference where she will talk with many other scientists. Later, she will write a paper to be published in a scientific journal. After she submits the paper, several scientists will review the paper - a process called peer review - to suggest further investigations or changes in interpretation to make the paper stronger. The scientists will then recommend or deny the paper for publication. Once it is published, other scientists incorporate the results into their own research. If they cannot replicate her results, her work will be thrown out! Scientific ideas are advanced after many papers on a topic are published. | text | null |
L_0296 | scientific community | T_1655 | There scientific community controls the quality and type of research that is done by project funding. Most scientific research is expensive, so scientists must write a proposal to a funding agency, such as the National Science Foun- dation or the National Aeronautics and Space Administration (NASA), to pay for equipment, supplies, and salaries. Scientific proposals are reviewed by other scientists in the field and are evaluated for funding. In many fields, the funding rate is low and the money goes only to the most worthy research projects. The scientific community monitors scientific integrity. During their training, students learn how to conduct good scientific experiments. They learn not to fake, hide, or selectively report data, and they learn how to fairly evaluate data and the work of other scientists. Scientists who do not have scientific integrity are strongly condemned by the scientific community. Nothing is perfect, but considering all the scientific research that is done, there are few incidences of scientific dishonesty. Yet when they do occur, they are often reported with great vehemence by the media. Often this causes the public to mistrust scientists in ways that are unwarranted. 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_0297 | scientific explanations and interpretations | T_1656 | Scientists usually begin an investigation with facts. A fact is a bit of information that is true. Facts come from data collected from observations or from experiments that have already been run. Data is factual information that is not subject to opinion or bias. What is a fact? Look at the following list and identify if the statement is a fact (from observation or prior experi- ments), an opinion, or a combination. Can you be sure from the photo that Susan has a cold? 1. 2. 3. 4. 5. 6. 7. Susan has long hair. Susan is sneezing and has itchy eyes. She is not well. She has a cold. Colds are caused by viruses. Echinacea is an herb that prevents colds. Bill Gates is the smartest man in the United States. People born under the astrological sign Leo are fiery, self-assured, and charming. Average global temperature has been rising at least since 1960. | text | null |
L_0297 | scientific explanations and interpretations | T_1657 | The following is an analysis of the statements above: 1. This is a fact made from observation. 2. The first part is from observations. The second is a fact drawn from the prior observations. The third is an opinion, since she might actually have allergies or the flu. Tests could be done to see what is causing her illness. 3. This is a fact. Many, many scientific experiments have shown that colds are caused by viruses. 4. While that sounds like a fact, the scientific evidence is mixed. One reputable study published in 2007 showed a decrease of 58%, but several other studies have shown no beneficial effect. 5. Bill Gates is the wealthiest man in the United States; thats a fact. But theres no evidence that hes also the smartest man, and chances are hes not. This is an opinion. 6. This sounds like a fact, but it is not. It is easy to test. Gather together a large number of subjects, each with a friend. Have the friends fill out a questionnaire describing the subject. Match the traits against the persons astrological sign to see if the astrological predictions fit. Are Leos actually more fiery, self assured, and charming? Tests like this have not supported the claims of astrologers, yet astrologers have not modified their opinions. 7. This is a fact. The Figure 1.2 shows the temperature anomaly since 1880. Theres no doubt that temperature has risen overall since 1880 and especially since the late 1970s. Global Average Annual Temperatures are Rising. This graph shows temperature anomaly relative to the 1951-1980 aver- age (the average is made to be 0). The green bars show uncertainty. | text | null |
L_0298 | scientific method | T_1658 | The goal of science is to answer questions about the natural world. Scientific questions must be testable. Which of these two questions is a good scientific question and which is not? What is the age of our planet Earth? How many angels can dance on the head of a pin? The first is a good scientific question that can be answered by radiometrically dating rocks among other techniques. The second cannot be answered using data, so it is not a scientific question. | text | null |
L_0298 | scientific method | T_1659 | Scientists use the scientific method to answer questions. The scientific method is a series of steps that help to investigate a question. Often, students learn that the scientific method is a linear process that goes like this: Ask a question. The question is based on one or more observations or on data from a previous experiment. Do some background research. Create a hypothesis. Do experiments or make observations to test the hypothesis. Gather the data. Formulate a conclusion. The process doesnt always go in a straight line. A scientist might ask a question, then do some background research and discover that the question needed to be asked a different way, or that a different question should be asked. Click image to the left or use the URL below. URL: | text | null |
L_0298 | scientific method | T_1660 | Now, lets ask a scientific question. Remember that it must be testable. We learned above that average global temperature has been rising since record keeping began in 1880. We know that carbon dioxide is a greenhouse gas. Greenhouse gases trap heat in the atmosphere. This leads us to a question: Question: Is the amount of carbon dioxide in Earths atmosphere changing? This is a good scientific question because it is testable. How has carbon dioxide in the atmosphere changed over those 50-plus years (see Figure 1.1)? About how much has atmospheric CO2 risen between 1958 and 2011 in parts per million? | text | null |
L_0298 | scientific method | T_1661 | So weve answered the question using data from research that has already been done. If scientists had not been monitoring CO2 levels over the years, wed have had to start these measurements now. Because this question can be answered with data, it is testable. Click image to the left or use the URL below. URL: | text | null |
L_0325 | temperature of the atmosphere | T_1753 | The atmosphere is layered, corresponding with how the atmospheres temperature changes with altitude. By under- standing the way temperature changes with altitude, we can learn a lot about how the atmosphere works. | text | null |
L_0325 | temperature of the atmosphere | T_1754 | Why does warm air rise (Figure 1.1)? Gas molecules are able to move freely, and if they are uncontained, as they are in the atmosphere, they can take up more or less space. When gas molecules are cool, they are sluggish and do not take up as much space. With the same number of molecules in less space, both air density and air pressure are higher. When gas molecules are warm, they move vigorously and take up more space. Air density and air pressure are lower. Warmer, lighter air is more buoyant than the cooler air above it, so it rises. The cooler air then sinks down, because it is denser than the air beneath it. This is convection, which was described in the chapter Plate Tectonics. | text | null |
L_0325 | temperature of the atmosphere | T_1755 | The property that changes most strikingly with altitude is air temperature. Unlike the change in pressure and density, which decrease with altitude, changes in air temperature are not regular. A change in temperature with distance is called a temperature gradient. | text | null |
L_0325 | temperature of the atmosphere | T_1756 | The atmosphere is divided into layers based on how the temperature in that layer changes with altitude, the layers temperature gradient (Figure 1.2). The temperature gradient of each layer is different. In some layers, temperature increases with altitude and in others it decreases. The temperature gradient in each layer is determined by the heat source of the layer (See opening image). The four main layers of the atmosphere have different temperature gradients, cre- ating the thermal structure of the atmo- sphere. This video is very thorough in its discussion of the layers of the atmosphere. Remember that the chemical composi- tion of each layer is nearly the same except for the ozone layer that is found in the stratosphere. Click image to the left or use the URL below. URL: | text | null |
L_0332 | tornadoes | T_1782 | Tornadoes, also called twisters, are fierce products of severe thunderstorms (Figure 1.1). As air in a thunderstorm rises, the surrounding air races in to fill the gap. This forms a tornado, a funnel-shaped, whirling column of air extending downward from a cumulonimbus cloud. A tornado lasts from a few seconds to several hours. The average wind speed is about 177 kph (110 mph), but some winds are much faster. A tornado travels over the ground at about 45 km per hour (28 miles per hour) and goes about 25 km (16 miles) before losing energy and disappearing (Figure 1.2). The formation of this tornado outside Dimmit, Texas, in 1995 was well studied. This tornado struck Seymour, Texas, in 1979. | text | null |
L_0332 | tornadoes | T_1782 | Tornadoes, also called twisters, are fierce products of severe thunderstorms (Figure 1.1). As air in a thunderstorm rises, the surrounding air races in to fill the gap. This forms a tornado, a funnel-shaped, whirling column of air extending downward from a cumulonimbus cloud. A tornado lasts from a few seconds to several hours. The average wind speed is about 177 kph (110 mph), but some winds are much faster. A tornado travels over the ground at about 45 km per hour (28 miles per hour) and goes about 25 km (16 miles) before losing energy and disappearing (Figure 1.2). The formation of this tornado outside Dimmit, Texas, in 1995 was well studied. This tornado struck Seymour, Texas, in 1979. | text | null |
L_0332 | tornadoes | T_1783 | An individual tornado strikes a small area, but it can destroy everything in its path. Most injuries and deaths from tornadoes are caused by flying debris (Figure 1.3). In the United States an average of 90 people are killed by tornadoes each year. The most violent two percent of tornadoes account for 70% of the deaths by tornadoes. | text | null |
L_0332 | tornadoes | T_1784 | Tornadoes form at the front of severe thunderstorms. Lines of these thunderstorms form in the spring where where maritime tropical (mT) and continental polar (cP) air masses meet. Although there is an average of 770 tornadoes annually, the number of tornadoes each year varies greatly (Figure 1.4). | text | null |
L_0332 | tornadoes | T_1785 | In late April 2011, severe thunderstorms pictured in the satellite image spawned the deadliest set of tornadoes in more than 25 years. In addition to the meeting of cP and mT mentioned above, the jet stream was blowing strongly Tornado damage at Ringgold, Georgia in April 2011. The frequency of F3, F4, and F5 torna- does in the United States. The red region that starts in Texas and covers Oklahoma, Nebraska, and South Dakota is called Tornado Alley because it is where most of the violent tornadoes occur. in from the west. The result was more than 150 tornadoes reported throughout the day (Figure 1.5). The entire region was alerted to the possibility of tornadoes in those late April days. But meteorologists can only predict tornado danger over a very wide region. No one can tell exactly where and when a tornado will touch down. Once a tornado is sighted on radar, its path is predicted and a warning is issued to people in that area. The exact path is unknown because tornado movement is not very predictable. | text | null |
L_0332 | tornadoes | T_1785 | In late April 2011, severe thunderstorms pictured in the satellite image spawned the deadliest set of tornadoes in more than 25 years. In addition to the meeting of cP and mT mentioned above, the jet stream was blowing strongly Tornado damage at Ringgold, Georgia in April 2011. The frequency of F3, F4, and F5 torna- does in the United States. The red region that starts in Texas and covers Oklahoma, Nebraska, and South Dakota is called Tornado Alley because it is where most of the violent tornadoes occur. in from the west. The result was more than 150 tornadoes reported throughout the day (Figure 1.5). The entire region was alerted to the possibility of tornadoes in those late April days. But meteorologists can only predict tornado danger over a very wide region. No one can tell exactly where and when a tornado will touch down. Once a tornado is sighted on radar, its path is predicted and a warning is issued to people in that area. The exact path is unknown because tornado movement is not very predictable. | text | null |
L_0332 | tornadoes | T_1786 | The intensity of tornadoes is measured on the Fujita Scale (see Table 1.1), which assigns a value based on wind speed and damage. F Scale F0 (km/hr) 64-116 (mph) 40-72 F1 117-180 73-112 F2 181-253 113-157 F3 254-333 158-206 F4 333-419 207-260 F5 420-512 261-318 F6 >512 >318 Damage Light - tree branches fall and chimneys may col- lapse Moderate - mobile homes, autos pushed aside Considerable - roofs torn off houses, large trees up- rooted Severe - houses torn apart, trees uprooted, cars lifted Devastating - houses lev- eled, cars thrown Incredible - structures fly, cars become missiles Maximum tornado wind speed Click image to the left or use the URL below. URL: | text | null |
L_0339 | types of marine organisms | T_1806 | The smallest and largest animals on Earth live in the oceans. Why do you think the oceans can support large animals? Marine animals breathe air or extract oxygen from the water. Some float on the surface and others dive into the oceans depths. There are animals that eat other animals, and plants generate food from sunlight. A few bizarre creatures break down chemicals to make food! The following section divides ocean life into seven basic groups. | text | null |
L_0339 | types of marine organisms | T_1807 | Plankton are organisms that cannot swim but that float along with the current. The word "plankton" comes from the Greek for wanderer. Most plankton are microscopic, but some are visible to the naked eye (Figure 1.1). Phytoplankton are tiny plants that make food by photosynthesis. Because they need sunlight, phytoplankton live in the photic zone. Phytoplankton are responsible for about half of the total primary productivity (food energy) on Earth. Like other plants, phytoplankton release oxygen as a waste product. Microscopic diatoms are a type of phyto- plankton. Zooplankton, or animal plankton, eat phytoplankton as their source of food (Figure 1.2). Some zooplankton live as plankton all their lives and others are juvenile forms of animals that will attach to the bottom as adults. Some small invertebrates live as zooplankton. Copepods are abundant and so are an important food source for larger animals. | text | null |
L_0339 | types of marine organisms | T_1807 | Plankton are organisms that cannot swim but that float along with the current. The word "plankton" comes from the Greek for wanderer. Most plankton are microscopic, but some are visible to the naked eye (Figure 1.1). Phytoplankton are tiny plants that make food by photosynthesis. Because they need sunlight, phytoplankton live in the photic zone. Phytoplankton are responsible for about half of the total primary productivity (food energy) on Earth. Like other plants, phytoplankton release oxygen as a waste product. Microscopic diatoms are a type of phyto- plankton. Zooplankton, or animal plankton, eat phytoplankton as their source of food (Figure 1.2). Some zooplankton live as plankton all their lives and others are juvenile forms of animals that will attach to the bottom as adults. Some small invertebrates live as zooplankton. Copepods are abundant and so are an important food source for larger animals. | text | null |
L_0339 | types of marine organisms | T_1808 | The few true plants found in the oceans include salt marsh grasses and mangrove trees. Although they are not true plants, large algae, which are called seaweed, also use photosynthesis to make food. Plants and seaweeds are found in the neritic zone, where the light they need penetrates so that they can photosynthesize (Figure 1.3). Kelp grows in forests in the neritic zone. Otters and other organisms depend on the kelp-forest ecosystem. | text | null |
L_0339 | types of marine organisms | T_1809 | The variety and number of invertebrates, animals without a backbone, is truly remarkable (Figure 1.4). Marine invertebrates include sea slugs, sea anemones, starfish, octopuses, clams, sponges, sea worms, crabs, and lobsters. Most of these animals are found close to the shore, but they can be found throughout the ocean. Jellies are otherworldly creatures that glow in the dark, without brains or bones, some more than 100 feet long. Along with many other ocean areas, they live just off Californias coast. Click image to the left or use the URL below. URL: | text | null |
L_0339 | types of marine organisms | T_1810 | Fish are vertebrates; they have a backbone. What are some of the features fish have that allows them to live in the oceans? All fish have most or all of these traits: Fins with which to move and steer. Scales for protection. Gills for extracting oxygen from the water. A swim bladder that lets them rise and sink to different depths. (a) Mussels; (b) Crown of thorns sea star; (c) Moon jelly; (d) A squid. Ectothermy (cold-bloodedness), so that their bodies are the same temperature as the surrounding water. Bioluminescence, or light created from a chemical reaction that can attract prey or mates in the dark ocean. Included among the fish are sardines, salmon, and eels, as well as the sharks and rays (which lack swim bladders) (Figure 1.5). | text | null |
L_0339 | types of marine organisms | T_1811 | Only a few types of reptiles live in the oceans and they live in warm water. Why are reptiles so restricted in their ability to live in the sea? Sea turtles, sea snakes, saltwater crocodiles, and marine iguana that are found only at the Galapagos Islands sum up the marine reptile groups (Figure 1.6). Sea snakes bear live young in the ocean, but turtles, crocodiles, and marine iguanas all lay their eggs on land. The Great White Shark is a fish that preys on other fish and marine mammals. Sea turtles are found all over the oceans, but their numbers are diminishing. | text | null |
L_0339 | types of marine organisms | T_1811 | Only a few types of reptiles live in the oceans and they live in warm water. Why are reptiles so restricted in their ability to live in the sea? Sea turtles, sea snakes, saltwater crocodiles, and marine iguana that are found only at the Galapagos Islands sum up the marine reptile groups (Figure 1.6). Sea snakes bear live young in the ocean, but turtles, crocodiles, and marine iguanas all lay their eggs on land. The Great White Shark is a fish that preys on other fish and marine mammals. Sea turtles are found all over the oceans, but their numbers are diminishing. | text | null |
L_0339 | types of marine organisms | T_1812 | Many types of birds are adapted to living in the sea or on the shore. With their long legs for wading and long bills for digging in sand for food, shorebirds are well adapted for the intertidal zone. Many seabirds live on land but go to sea to fish, such as gulls, pelicans, and frigate birds. Some birds, like albatross, spend months at sea and only come on shore to raise chicks (Figure 1.7). | text | null |
L_0339 | types of marine organisms | T_1813 | What are the common traits of mammals? Mammals are endothermic (warm-blooded) vertebrates that give birth to live young, feed them with milk, and have hair, ears, and a jaw bone with teeth. What traits might mammals have to be adapted to life in the ocean? (a) Shorebirds; (b) Seabirds; (c) Albatross. For swimming: streamlined bodies, slippery skin or hair, fins. For warmth: fur, fat, high metabolic rate, small surface area to volume, specialized blood system. For salinity: kidneys that excrete salt, impervious skin. The five types of marine mammals are pictured here: (Figure 1.8). (a) Cetaceans: whales, dolphins, and porpoises. (b) Sirenians: manatee and the dugong. (c) Mustelids: Sea otters (terrestrial members are skunks, badgers and weasels). (d) Pinnipeds: Seals, sea lions, and walruses. (e) Polar bear. | text | null |
L_0339 | types of marine organisms | T_1813 | What are the common traits of mammals? Mammals are endothermic (warm-blooded) vertebrates that give birth to live young, feed them with milk, and have hair, ears, and a jaw bone with teeth. What traits might mammals have to be adapted to life in the ocean? (a) Shorebirds; (b) Seabirds; (c) Albatross. For swimming: streamlined bodies, slippery skin or hair, fins. For warmth: fur, fat, high metabolic rate, small surface area to volume, specialized blood system. For salinity: kidneys that excrete salt, impervious skin. The five types of marine mammals are pictured here: (Figure 1.8). (a) Cetaceans: whales, dolphins, and porpoises. (b) Sirenians: manatee and the dugong. (c) Mustelids: Sea otters (terrestrial members are skunks, badgers and weasels). (d) Pinnipeds: Seals, sea lions, and walruses. (e) Polar bear. | text | null |
L_0352 | weather fronts | T_1877 | Two air masses meet at a front. At a front, the two air masses have different densities and do not easily mix. One air mass is lifted above the other, creating a low pressure zone. If the lifted air is moist, there will be condensation and precipitation. Winds are common at a front. The greater the temperature difference between the two air masses, the stronger the winds will be. Fronts are the main cause of stormy weather. There are four types of fronts, three moving and one stationary. With cold fronts and warm fronts, the air mass at the leading edge of the front gives the front its name. In other words, a cold front is right at the leading edge of moving cold air and a warm front marks the leading edge of moving warm air. | text | null |
L_0352 | weather fronts | T_1878 | At a stationary front the air masses do not move (Figure 1.1). A front may become stationary if an air mass is stopped by a barrier, such as a mountain range. A stationary front may bring days of rain, drizzle, and fog. Winds usually blow parallel to the front, but in opposite directions. After several days, the front will likely break apart. | text | null |
L_0352 | weather fronts | T_1879 | When a cold air mass takes the place of a warm air mass, there is a cold front (Figure 1.2). The map symbol for a stationary front has red domes for the warm air mass and blue triangles for the cold air mass. Imagine that you are standing in one spot as a cold front approaches. Along the cold front, the denser, cold air pushes up the warm air, causing the air pressure to decrease (Figure 1.2). If the humidity is high enough, some types of cumulus clouds will grow. High in the atmosphere, winds blow ice crystals from the tops of these clouds to create cirrostratus and cirrus clouds. At the front, there will be a line of rain showers, snow showers, or thunderstorms with blustery winds (Figure 1.3). A squall line is a line of severe thunderstorms that forms along a cold front. Behind the front is the cold air mass. This mass is drier, so precipitation stops. The weather may be cold and clear or only partly cloudy. Winds may continue to blow into the low pressure zone at the front. The weather at a cold front varies with the season. Spring and summer: the air is unstable so thunderstorms or tornadoes may form. Spring: if the temperature gradient is high, strong winds blow. Autumn: strong rains fall over a large area. Winter: the cold air mass is likely to have formed in the frigid arctic, so there are frigid temperatures and heavy snows. | text | null |
L_0352 | weather fronts | T_1879 | When a cold air mass takes the place of a warm air mass, there is a cold front (Figure 1.2). The map symbol for a stationary front has red domes for the warm air mass and blue triangles for the cold air mass. Imagine that you are standing in one spot as a cold front approaches. Along the cold front, the denser, cold air pushes up the warm air, causing the air pressure to decrease (Figure 1.2). If the humidity is high enough, some types of cumulus clouds will grow. High in the atmosphere, winds blow ice crystals from the tops of these clouds to create cirrostratus and cirrus clouds. At the front, there will be a line of rain showers, snow showers, or thunderstorms with blustery winds (Figure 1.3). A squall line is a line of severe thunderstorms that forms along a cold front. Behind the front is the cold air mass. This mass is drier, so precipitation stops. The weather may be cold and clear or only partly cloudy. Winds may continue to blow into the low pressure zone at the front. The weather at a cold front varies with the season. Spring and summer: the air is unstable so thunderstorms or tornadoes may form. Spring: if the temperature gradient is high, strong winds blow. Autumn: strong rains fall over a large area. Winter: the cold air mass is likely to have formed in the frigid arctic, so there are frigid temperatures and heavy snows. | text | null |
L_0352 | weather fronts | T_1880 | At a warm front, a warm air mass slides over a cold air mass (Figure 1.4). When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable. Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching. The transition from cold air to warm air takes place over a long distance, so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other. Warm air moves forward to take over the position of colder air. Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray. Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches. As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that. The weather worsens. As the warm air mass approaches, temperatures rise and snow turns to sleet and freezing rain. Warm and cold air mix at the front, leading to the formation of stratus clouds and fog (Figure 1.5). Cumulus clouds build at a warm front. | text | null |
L_0352 | weather fronts | T_1880 | At a warm front, a warm air mass slides over a cold air mass (Figure 1.4). When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable. Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching. The transition from cold air to warm air takes place over a long distance, so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other. Warm air moves forward to take over the position of colder air. Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray. Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches. As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that. The weather worsens. As the warm air mass approaches, temperatures rise and snow turns to sleet and freezing rain. Warm and cold air mix at the front, leading to the formation of stratus clouds and fog (Figure 1.5). Cumulus clouds build at a warm front. | text | null |
L_0352 | weather fronts | T_1880 | At a warm front, a warm air mass slides over a cold air mass (Figure 1.4). When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable. Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching. The transition from cold air to warm air takes place over a long distance, so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other. Warm air moves forward to take over the position of colder air. Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray. Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches. As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that. The weather worsens. As the warm air mass approaches, temperatures rise and snow turns to sleet and freezing rain. Warm and cold air mix at the front, leading to the formation of stratus clouds and fog (Figure 1.5). Cumulus clouds build at a warm front. | text | null |
L_0352 | weather fronts | T_1881 | An occluded front usually forms around a low pressure system (Figure 1.6). The occlusion starts when a cold front catches up to a warm front. The air masses, in order from front to back, are cold, warm, and then cold again. The map symbol for an occluded front is mixed cold front triangles and warm front domes. Coriolis effect curves the boundary where the two fronts meet towards the pole. If the air mass that arrives third is colder than either of the first two air masses, that air mass slip beneath them both. This is called a cold occlusion. If the air mass that arrives third is warm, that air mass rides over the other air mass. This is called a warm occlusion (Figure 1.7). The weather at an occluded front is especially fierce right at the occlusion. Precipitation and shifting winds are typical. The Pacific Coast has frequent occluded fronts. An occluded front with the air masses from front to rear in order as cold, warm, cold. 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_0352 | weather fronts | T_1881 | An occluded front usually forms around a low pressure system (Figure 1.6). The occlusion starts when a cold front catches up to a warm front. The air masses, in order from front to back, are cold, warm, and then cold again. The map symbol for an occluded front is mixed cold front triangles and warm front domes. Coriolis effect curves the boundary where the two fronts meet towards the pole. If the air mass that arrives third is colder than either of the first two air masses, that air mass slip beneath them both. This is called a cold occlusion. If the air mass that arrives third is warm, that air mass rides over the other air mass. This is called a warm occlusion (Figure 1.7). The weather at an occluded front is especially fierce right at the occlusion. Precipitation and shifting winds are typical. The Pacific Coast has frequent occluded fronts. An occluded front with the air masses from front to rear in order as cold, warm, cold. 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_0353 | weather maps | T_1882 | Weather maps simply and graphically depict meteorological conditions in the atmosphere. Weather maps may display only one feature of the atmosphere or multiple features. They can depict information from computer models or from human observations. On a weather map, important meteorological conditions are plotted for each weather station. Meteorologists use many different symbols as a quick and easy way to display information on the map (Figure 1.1). Once conditions have been plotted, points of equal value can be connected by isolines. Weather maps can have many types of connecting lines. For example: Explanation of some symbols that may appear on a weather map. Lines of equal temperature are called isotherms. Isotherms show temperature gradients and can indicate the location of a front. In terms of precipitation, what does the 0o C (32o F) isotherm show? Isobars are lines of equal average air pressure at sea level (Figure 1.2). Closed isobars represent the locations of high and low pressure cells. Isotachs are lines of constant wind speed. Where the minimum values occur high in the atmosphere, tropical cyclones may develop. The highest wind speeds can be used to locate the jet stream. Surface weather analysis maps are weather maps that only show conditions on the ground (Figure 1.3). Surface analysis maps may show sea level mean pressure, temperature, and amount of cloud cover. Click image to the left or use the URL below. URL: | text | null |
L_0353 | weather maps | T_1882 | Weather maps simply and graphically depict meteorological conditions in the atmosphere. Weather maps may display only one feature of the atmosphere or multiple features. They can depict information from computer models or from human observations. On a weather map, important meteorological conditions are plotted for each weather station. Meteorologists use many different symbols as a quick and easy way to display information on the map (Figure 1.1). Once conditions have been plotted, points of equal value can be connected by isolines. Weather maps can have many types of connecting lines. For example: Explanation of some symbols that may appear on a weather map. Lines of equal temperature are called isotherms. Isotherms show temperature gradients and can indicate the location of a front. In terms of precipitation, what does the 0o C (32o F) isotherm show? Isobars are lines of equal average air pressure at sea level (Figure 1.2). Closed isobars represent the locations of high and low pressure cells. Isotachs are lines of constant wind speed. Where the minimum values occur high in the atmosphere, tropical cyclones may develop. The highest wind speeds can be used to locate the jet stream. Surface weather analysis maps are weather maps that only show conditions on the ground (Figure 1.3). Surface analysis maps may show sea level mean pressure, temperature, and amount of cloud cover. Click image to the left or use the URL below. URL: | text | null |
L_0353 | weather maps | T_1882 | Weather maps simply and graphically depict meteorological conditions in the atmosphere. Weather maps may display only one feature of the atmosphere or multiple features. They can depict information from computer models or from human observations. On a weather map, important meteorological conditions are plotted for each weather station. Meteorologists use many different symbols as a quick and easy way to display information on the map (Figure 1.1). Once conditions have been plotted, points of equal value can be connected by isolines. Weather maps can have many types of connecting lines. For example: Explanation of some symbols that may appear on a weather map. Lines of equal temperature are called isotherms. Isotherms show temperature gradients and can indicate the location of a front. In terms of precipitation, what does the 0o C (32o F) isotherm show? Isobars are lines of equal average air pressure at sea level (Figure 1.2). Closed isobars represent the locations of high and low pressure cells. Isotachs are lines of constant wind speed. Where the minimum values occur high in the atmosphere, tropical cyclones may develop. The highest wind speeds can be used to locate the jet stream. Surface weather analysis maps are weather maps that only show conditions on the ground (Figure 1.3). Surface analysis maps may show sea level mean pressure, temperature, and amount of cloud cover. Click image to the left or use the URL below. URL: | text | null |
L_0354 | weather versus climate | T_1883 | All weather takes place in the atmosphere, virtually all of it in the lower atmosphere. Weather describes what the atmosphere is like at a specific time and place. A locations weather depends on: air temperature air pressure fog humidity cloud cover precipitation wind speed and direction All of these characteristics are directly related to the amount of energy that is in the system and where that energy is. The ultimate source of this energy is the Sun. Weather is the change we experience from day to day. Weather can change rapidly. | text | null |
L_0354 | weather versus climate | T_1884 | Although almost anything can happen with the weather, climate is more predictable. The weather on a particular winter day in San Diego may be colder than on the same day in Lake Tahoe, but, on average, Tahoes winter climate is significantly colder than San Diegos (Figure 1.1). Climate is the long-term average of weather in a particular spot. Good climate is why we choose to vacation in Hawaii in February, even though the weather is not guaranteed to be good! A locations climate can be described by its air temperature, humidity, wind speed and direction, and the type, quantity, and frequency of precipitation. The climate for a particular place is steady, and changes only very slowly. Climate is determined by many factors, including the angle of the Sun, the likelihood of cloud cover, and the air pressure. All of these factors are related to the amount of energy that is found in that location over time. The climate of a region depends on its position relative to many things. These factors are described in the next sections. 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_0357 | wind power | T_1890 | Energy from the Sun also creates wind, which can be used as wind power. The Sun heats different locations on Earth by different amounts. Air that becomes warm rises and then sucks cooler air into that spot. The movement of air from one spot to another along the ground creates wind. Since wind is moving, it has kinetic energy. Wind power is the fastest growing renewable energy source in the world. Windmills are now seen in many locations, either individually or, more commonly, in large fields. | text | null |
L_0357 | wind power | T_1891 | Wind is the source of energy for wind power. Wind has been used for power for centuries. For example, windmills were used to grind grain and pump water. Sailing ships traveled by wind power long before ships were powered by fossil fuels. Wind can be used to generate electricity, as the moving air spins a turbine to create electricity (Figure Click image to the left or use the URL below. URL: | text | null |
L_0357 | wind power | T_1892 | Wind power has many advantages. It does not burn, so it does not release pollution or carbon dioxide. Also, wind is plentiful in many places. Wind, however, does not blow all of the time, even though power is needed all of the time. Just as with solar power, engineers are working on technologies that can store wind power for later use. Windmills are expensive and wear out quickly. A lot of windmills are needed to power a region, so nearby residents may complain about the loss of a nice view if a wind farm is built. Coastlines typically receive a lot of wind, but wind farms built near beaches may cause unhappiness for local residents and tourists. The Cape Wind project off of Cape Cod, Massachusetts has been approved but is generating much controversy. Opponents are in favor of green power but not at that location. Proponents say that clean energy is needed and the project would supply 75% of the electricity needed for Cape Cod and nearby islands (Figure 1.2). California was an early adopter of wind power. Windmills are found in mountain passes, where the cooler Pacific Ocean air is sucked through on its way to warmer inland valleys. Large fields of windmills can be seen at Altamont Pass in the eastern San Francisco Bay Area, San Gorgonio Pass east of Los Angeles, and Tehachapi Pass at the southern end of the San Joaquin Valley. | text | null |
L_0359 | scientific ways of thinking | T_1898 | Most people think of science as a collection of facts or a body of knowledge. For example, you may have memorized the processes of the water cycle. As shown in Figure 1.1, the processes include evaporation and precipitation. Such knowledge of the natural world is only part of what science is. Science is as much about doing as knowing. Science is a way of learning about the natural world that depends on evidence, reasoning, and repeated testing. Scientists explain the world based on their observations. If they develop new ideas about the way the world works, they set up ways to test these new ideas. Scientific knowledge keeps changing because scientists are always doing science. | text | null |
L_0359 | scientific ways of thinking | T_1899 | When Miranda and Jeanny wondered whether bacteria might decompose plastic, they were thinking like a scientist. What does it mean to think like a scientist? A scientist is observant. Miranda and Jeanny observed all the plastic trash when they visited a landfill. They also saw a lot of plastic trash along a local river. A scientist wonders and asks questions. Miranda and Jeanny wondered if any bacteria could help break down plastic. They asked: Can some bacteria consume chemicals in plastic for food? A scientist tries to find answers using evidence and logic. Often, a scientist does experiments to gather more evidence and test ideas. Miranda and Jeanny did a lot of online research to find out what other scientists had already learned. Then they did their own experiments. They gathered and tested bacteria. For example, they grew bacteria on gel like the red gel in Figure 1.2. You can learn the details of their research and their amazing results by watching this video: A scientist is skeptical. Claims must be backed by adequate evidence. Miranda and Jeanny repeated their experiments so they were confident in their results. Only then did they draw conclusions. A scientist has an open mind. Scientific knowledge is always evolving as new evidence comes in. Miranda and Jeanny made an important contribution with the evidence they gathered. They discovered two species of bacteria that could consume a harmful chemical in plastic. | text | null |
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