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cycles of matter | T_0342 | Living things also need nitrogen. Nitrogen is a key element in proteins. Like carbon, nitrogen cycles through ecosystems. You can see the nitrogen cycle in Figure 18.13. |
cycles of matter | T_0343 | Air is about 78 percent nitrogen. Decomposers release nitrogen into the air from dead organisms and their wastes. However, producers such as plants cant use these forms of nitrogen. Nitrogen must combine with other elements before producers can use it. This is done by certain bacteria in the soil. Its called fixing nitrogen. |
cycles of matter | T_0344 | Nitrogen is one of the most important nutrients needed by plants. Thats why most plant fertilizers contain nitrogen. Adding fertilizer to soil allows more plants to grow. As a result, a given amount of land can produce more food. So far, so good. But what happens next? Rain dissolves fertilizer in the soil. Runoff carries it away. The fertilizer ends up in bodies of water, from ponds to oceans. The nitrogen is a fertilizer in the water bodies. Since there is a lot of nitrogen it causes algae to grow out of control. Figure 18.14 shows a pond covered with algae. Algae may use up so much oxygen in the water that nothing else can grow. Soon, even the algae die out. Decomposers break down the dead tissue and use up all the oxygen in the water. This creates a dead zone. A dead zone is an area in a body of water where nothing grows because there is too little oxygen. There is a large dead zone in the Gulf of Mexico. You can see it Figure 18.14. |
the human population | T_0345 | A population usually grows when it has what it needs. If theres plenty of food and other resources, the population will get bigger. Look at Table 18.1. It shows how a population of bacteria grew. A single bacteria cell was added to a container of nutrients. Conditions were ideal. The bacteria divided every 30 minutes. After just 10 hours, there were more than a million bacteria! Assume the bacteria population keeps growing at this rate. How many bacteria will there be at 10.5 hours? Or at 12 hours? Time (hours) 0 0.5 Number of Bacteria 1 2 Time (hours) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10 Number of Bacteria 4 8 16 32 64 128 256 512 1,024 2,048 4,096 8,192 16,384 32,768 65,536 131,072 262,144 524,288 1,048,576 |
the human population | T_0346 | The population growth rate is how fast a population is growing. The letter r stands for the growth rate. The growth rate equals the number of new members added to the population in a year for each 100 members already in the population. The growth rate includes new members added to the population and old members removed from the population. Births add new members to the population. Deaths remove members from the population. The formula for population growth rate is: r = b - d, where b = birth rate (number of births in 1 year per 100 population members) d = death rate (number of deaths in 1 year per 100 population members) If the birth rate is greater than the death rate, r is positive. This means that the population is growing bigger. For example, if b = 10 and d = 8, r = 2. This means that the population is growing by 2 individuals per year for every 100 members of the population. This may not sound like much, but its a fairly high rate of growth. A population growing at this rate would double in size in just 35 years! If the birth rate is less than the death rate, r is negative. This means that the population is becoming smaller. What do you think might cause this to happen? |
the human population | T_0347 | A population cant keep growing bigger and bigger forever. Sooner or later, it will run out of things it needs. For a given species, there is a maximum population that can be supported by the environment. This maximum is called the carrying capacity. When a population gets close to the carrying capacity, it usually grows more slowly. You can see this in Figure 18.16. When the population reaches the carrying capacity, it stops growing. |
the human population | T_0348 | Figure 18.17 shows how the human population has grown. It grew very slowly for tens of thousands of years. Then, in the 1800s, something happened to change all that. The human population started to grow much faster. |
the human population | T_0349 | The industrial revolution is what happened. The industrial revolution began in the late 1700s in Europe, North America, and a few other places. In these places, the human population grew faster. While there had always been a lot of births, the population grew because the death rate fell. It fell for several reasons: 1. New farm machines were invented. They increased the amount of food that could be produced. With more food, people were healthier and could live longer. 2. Steam engines and railroads were built. These machines could quickly carry food long distances. This made food shortages less likely. 3. Sanitation was improved. Sewers were dug to carry away human wastes (see Figure 18.18). This helped reduce the spread of disease. With better food and less chance of disease, the death rate fell. More children lived long enough to reach adulthood and have children of their own. As the death rate fell, the birth rate stayed high for a while. This caused rapid population growth. However, the birth rate in these countries has since fallen to a rate close to that of the low death rate. The result was slow population growth once again. These changes are called the demographic transition. |
the human population | T_0350 | More recently, the death rate has fallen because of the availability of more food and medical advances: A green revolution began in the mid 1900s. New methods and products increased how much food could be grown. For example, chemicals were developed that killed weeds without harming crops. Pesticides were developed that killed pests that destroyed crops. Vaccinations were developed that could prevent many diseases (see Figure 18.19). Antibiotics were discov- ered that could cure most infections caused by bacteria. Together, these two advances saved countless lives. Today in many countries, death rates have gone down but birth rates remain high. This means that the population is growing. Figure 18.20 shows the growth rates of human populations all over the world. |
the human population | T_0351 | The growth of the human population has started to slow down. You can see this in Figure 18.21. It may stop growing by the mid 2000s. Scientists think that the human population will peak at about 9 billion people. What will need to change for the population to stop growing then? |
the human population | T_0352 | Are 9 billion people the human carrying capacity? It looks that way in Figure 18.21. But some people think there are too many of us already. Thats because we are harming the environment. Supplying all those people with energy creates a lot of pollution. For example, huge oil spills have killed millions of living things. Burning fossil fuels pollutes the air. This also increases causes global warming. Fossil fuels and other resources are being used up. We may run out of oil by the mid 2000s. Many other resources will run out sooner or later. People are killing too many animals for food. For example, some of the best fishing grounds in the oceans have almost no fish left. People have destroyed many habitats. For example, theyve drained millions of acres of wetlands. Wetlands have a great diversity of species. As wetlands shrink, species go extinct. People have allowed alien or invasive species - species originally from a different area - to invade new habitats. Often, the aliens have no natural enemies in their new home. They may drive native species extinct. Figure People themselves are also affected by the large size of the human population. A minority of people use most of the worlds energy and other resources. Many other people lack resources. Many dont have enough to eat or live with |
the human population | T_0353 | Is it possible for all the worlds people to live well and still protect the planet? Thats the aim of sustainable development. Its goals are to: 1. Distribute resources fairly. 2. Conserve resources so they wont run out. 3. Use resources in ways that wont harm ecosystems. A smaller human population may be part of the solution. Better use of resources is another part. For example, when forests are logged, new trees should be planted. Everyone can help in the effort. What will you do? |
pollution of the land | T_0362 | Love Canal gained worldwide attention in the late 1970s when the press started covering its story. The story is outlined below and illustrated in Figure 19.9. |
pollution of the land | T_0363 | The Love Canal disaster actually began back in the mid 1900s. The disaster continues even today. Starting in the early 1940s, a big chemical company put thousands of barrels of chemical waste into an old canal. Over the next 10 years, the company dumped almost 22,000 tons of chemicals into the ground! In the early 1950s, the company covered over the barrels in the canal with soil. Then they sold the land to the city for just a dollar. The city needed the land in order to build an elementary school. The company warned the city that toxic waste was buried there. But they thought the waste was safe. The school and hundreds of homes were also built over the old canal. As it turned out, the cheap price was no bargain. Chemicals started leaking from the barrels. Chemicals seeped into basements. Chemicals bubbled up to the surface of the ground. In some places, plants wouldnt even grow on the soil. People noticed bad smells. Many got sick, especially the children. Residents wanted to know if the old chemicals were the cause. But they had a hard time getting officials to listen. So they demonstrated and demanded answers. Finally, the soil was tested and was found to be contaminated with harmful chemicals. For example, it contained a lot of lead and mercury. Both can cause permanent damage to the human nervous system. The school was closed. More than 200 homes were evacuated. Much of the Love Canal neighborhood was bulldozed away. The area had a massive clean-up effort. The cleanup cost millions of dollars. More than three decades later, much of Love Canal is still too contaminated to be safe for people. |
pollution of the land | T_0364 | Love Canal opened peoples eyes to toxic waste burial. They realized there must be other Love Canals all over the country. Thousands of contaminated sites were found. The Superfund Act was passed in 1980. The law required that money be set aside for cleanup of toxic waste sites, like the Elizabeth Copper Mine in Vermont (see the far-right image in Figure 19.9). The law also required safer disposal of hazardous waste in the future. |
pollution of the land | T_0365 | Love Canal highlighted the problem of pollution by hazardous waste. Hazardous waste is any waste that is dangerous to the health of people or the environment. It may be dangerous because it is toxic, corrosive, flammable, or explosive. Toxic waste is poisonous. Toxic waste may cause cancer or birth defects in people. It may also harm other living things. Corrosive waste is highly reactive with other substances. Corrosive waste may cause burns or destroy other materials that it touches. Flammable waste can burn easily. It may also give off harmful fumes when it burns. Explosive waste is likely to explode. The risk of explosion may be greater if the waste is mixed with other substances. Table 19.1 shows some examples of hazardous waste. Look closely. Are any of these examples lurking around your home? Example Description Cars contain toxic fluids such as brake fluid. The fluids may also be corrosive and flammable. This photo shows one way the fluids can end up in the ground. Cars use gas and oil. These materials are toxic and flammable. They pollute the land when they leak or spill. Batteries contain toxic and corrosive materials. People often toss them in the trash, but they should be disposed of properly. Electronics, such as old computers, contain toxic chem- icals. They may be sent to landfills where the toxic materials end up in the ground. Medical waste can contain many hazards: Human body fluids may cause disease; old thermometers may contain toxic mercury; and pharmaceuticals may be toxic to people and other living things. Example Description Paints can be both toxic and flammable. Paints may spill on the ground or be thrown improperly in the trash. Chemicals are applied to farm fields and lawns. They include fertilizers, herbicides, and pesticides. Many of these chemicals are toxic to people and other animals. |
pollution of the land | T_0366 | The greatest source of hazardous waste is industry. Agriculture is another major source. Even households produce a lot of hazardous waste. |
pollution of the land | T_0367 | Thanks to the lessons of Love Canal, the U.S. now has laws requiring the safe disposal of hazardous waste. Companies must ensure that hazardous waste is not allowed to enter the environment in dangerous amounts. They must also protect their workers from hazardous materials. For example, they must provide employees with the proper safety gear and training (see Figure 19.10). |
pollution of the land | T_0368 | Cleaning products, lawn chemicals, paints, batteries, motor oil these are just some of the many hazardous materials that may be found in households. You might think that a household doesnt produce enough hazardous waste to worry about. But when you add up all the waste from all the households in a community, its a different story. A city of just 50,000 people might produce more than 40 tons of hazardous waste each year! Clearly, how households deal with hazardous waste matters. What can your family do? Reduce, reuse, recycle, or properly dispose of the wastes. 1. Reduce the amount of hazardous products you buy. For example, if you only need a quart of paint for a job, dont buy a gallon. 2. Use less hazardous products if you can. For example, clean windows with vinegar and water instead of toxic window cleaners. 3. Reuse products if its safe to do so. For example, paint thinner that has been used to clean paint brushes can be strained and reused. 4. Recycle whenever possible. For example, some service stations allow you to drop off used motor oil, car batteries, or tires for recycling. 5. Always properly dispose of hazardous waste. For example, let liquid waste evaporate before placing the container in the trash. Proper disposal depends on the waste. Many hazardous products have disposal guidelines on the label. Thats one reason why you should keep the products in their original containers. The labels also explain how to use the products safely. Follow the instructions to protect yourself and the environment. Most communities have centers for disposing of household hazardous waste (see Figure 19.11). Do you know how to dispose of hazardous waste in your community? |
introduction to earths surface | T_0369 | To describe your location wherever you are on Earths surface, you could use a coordinate system. For example, you could say that you are at 1234 Main Street, Springfield, Ohio. Or you could use a point of reference. If you want to meet up with a friend, you could tell him the distance and direction you are from the reference point. An example is, I am at the corner of Maple Street and Main Street, about two blocks north of your apartment. When studying Earths surface, scientists must be able to pinpoint a feature they are interested in. Scientists and others have a system to describe the location of any feature. Usually they use latitude and longitude as a coordinate system. Lines of latitude and longitude form a grid. The grid is centered on a reference point. You will learn about this type of grid when we discuss maps later in this chapter. |
introduction to earths surface | T_0370 | When an object is moving, it is not enough to describe its location. We also need to know direction. Direction is important for describing moving objects. For example, a wind blows a storm over your school. Where is that storm coming from? Where is it going? The most common way to describe direction is by using a compass. A compass is a device with a floating needle (Figure 2.1). The needle is a small magnet that aligns itself with the Earths magnetic field. The compass needle always points to magnetic north. If you have a compass and you find north, you can then know any other direction. See the directions, such as east, south, west, etc., on a compass rose. A compass needle lines up with Earths magnetic north pole. This is different from Earths geographic north pole, or true north. The geographic north pole is the top of the imaginary axis around which Earth rotates. The geographic north pole is much like the spindle of a spinning top. The location of the geographic north pole does not change. However, the magnetic north pole shifts in location over time. Depending on where you live, you can correct for the difference between the two poles when you use a map and a compass (Figure 2.2). Some maps have a double compass rose. This allows users to make the corrections between magnetic north and true north. An example is a nautical chart that boaters use to chart their positions at sea (Figure 2.3). |
introduction to earths surface | T_0371 | As you know, the surface of Earth is not flat. Some places are high and some places are low. For example, mountain ranges like the Sierra Nevada in California or the Andes in South America are high above the surrounding areas. We can describe the topography of a region by measuring the height or depth of that feature relative to sea level (Figure mountains, while others are more like small hills! Relief, or terrain, includes all the landforms of a region. A topographic map shows the height, or elevation, of features in an area. This includes mountains, craters, valleys, and rivers. For example, Figure 2.5 shows the San Francisco Peaks in northern Arizona. Features on the map include mountains, hills and lava flows. You can recognize these features from the differences in elevation. We will talk about some different landforms in the next section. |
introduction to earths surface | T_0372 | If you take away the water in the oceans (Figure 2.6), Earth looks really different. You see that the surface has two main features: continents and ocean basins. Continents are large land areas. Ocean basins extend from the edges of continents to the ocean floor and into deep trenches. Continents are much older than ocean basins. Some rocks on the continents are billions of years old. Ocean basins are only millions of years old at their oldest. Because the continents are so old, a lot has happened to them! As we view the land around us we see landforms. Landforms are physical features on Earths surface. Landforms are introduced in this section but will be discussed more in later chapters. Constructive forces cause landforms to grow. Lava flowing into the ocean can build land outward. A volcano can be a constructive force. Destructive forces may blow landforms apart. A volcano blowing its top off is a destructive force. The destructive forces of weathering and erosion change landforms more slowly. Over millions of years, mountains are worn down by rivers and streams. Constructive and destructive forces work together to create landforms. Constructive forces create mountains and erosion may wear them away. Mountains are very large landforms. Mountains may wear away into a high flat area called a plateau, or a lower-lying plain. Interior plains are in the middle of continents. Coastal plains are on the edge of a continent, where it meets the ocean. Rivers and streams flow across continents. They cut away at rock, forming river valleys (Figure 2.8). These are |
introduction to earths surface | T_0373 | The ocean basin begins where the ocean meets the land. The continental margin begins at the shore and goes down to the ocean floor. It includes the continental shelf, slope, and rise. The continental shelf is part of the continent, but it is underwater today. It is about 100-200 meters deep, much shallower than the rest of the ocean. The continental shelf usually goes out about 100 to 200 kilometers from the shore (Figure 2.9). The continental slope is the slope that forms the edge of the continent. It is seaward of the continental shelf. In some places, a large pile of sediments brought from rivers creates the continental rise. The continental rise ends at the Besides seamounts, there are long, very tall (about 2 km) mountain ranges. These ranges are connected so that they form huge ridge systems called mid-ocean ridges (Figure 2.11). The mid-ocean ridges form from volcanic eruptions. Lava from inside Earth breaks through the crust and creates the mountains. The deepest places of the ocean are the ocean trenches. Many trenches line the edges of the Pacific Ocean. The Mariana Trench is the deepest place in the ocean. (Figure 2.12). At about 11 km deep, it is the deepest place on Earth! To compare, the tallest place on Earth, Mount Everest, is less than 9 km tall. |
modeling earths surface | T_0374 | Imagine you are going on a road trip. Perhaps you are going on vacation. How do you know where to go? Most likely, you will use a map. A map is a picture of specific parts of Earths surface. There are many types of maps. Each map gives us different information. Lets look at a road map, which is the probably the most common map that you use (Figure 2.13). |
modeling earths surface | T_0375 | Look for the legend on the top left side of the map. It explains how this map records different features. You can see the following: The boundaries of the state show its shape. Black dots represent the cities. Each city is named. The size of the dot represents the population of the city. Red and brown lines show major roads that connect the cities. Blue lines show rivers. Their names are written in blue. Blue areas show lakes and other waterways the Gulf of Mexico, Biscayne Bay, and Lake Okeechobee. Names for bodies of water are also written in blue. A line or scale of miles shows the distance represented on the map an inch or centimeter on the map represents a certain amount of distance (miles or kilometers). The legend explains other features and symbols on the map. It is the convention for north to be at the top of a map. For this reason, a compass rose is not needed on most maps. You can use this map to find your way around Florida and get from one place to another along roadways. |
modeling earths surface | T_0376 | There are many other types of maps besides road maps. Some examples include: Political or geographic maps show the outlines and borders of states and/or countries. Satellite view maps show terrains and vegetation forests, deserts, and mountains. Relief maps show elevations of areas, but usually on a larger scale, such as the whole Earth, rather than a local area. Topographic maps show detailed elevations of features on the map. Climate maps show average temperatures and rainfall. Precipitation maps show the amount of rainfall in different areas. Weather maps show storms, air masses, and fronts. Radar maps show storms and rainfall. Geologic maps detail the types and locations of rocks found in an area. These are but a few types of maps that various Earth scientists might use. You can easily carry a map around in your pocket or bag. Maps are easy to use because they are flat or two-dimensional. However, the world is three- dimensional. So, how do map makers represent a three-dimensional world on flat paper? |
modeling earths surface | T_0377 | Earth is a round, three-dimensional ball. In a small area, Earth looks flat, so it is not hard to make accurate maps of a small place. When map makers want to map the round Earth on flat paper, they use projections. What happens if you try to flatten out the skin of a peeled orange? Or if you try to gift wrap a soccer ball? To flatten out, the orange peel must rip and its shape must become distorted. To wrap around object with flat paper requires lots of extra cuts and folds. A projection is a way to represent Earths curved surface on flat paper (Figure 2.14). There are many types of projections. Each uses a different way to change three dimensions into two dimensions. There are two basic methods that the map maker uses in projections: The map maker slices the sphere in some way and unfolds it to make a flat map, like flattening out an orange peel. The map maker can look at the sphere from a certain point and then translate this view onto a flat paper. Lets look at a few commonly used projections. |
modeling earths surface | T_0378 | In 1569, Gerardus Mercator (1512-1594) (Figure 2.15) figured out a way to make a flat map of our round world, called the Mercator projection (Figure 2.16). Imagine wrapping the round, ball-shaped Earth with a big, flat piece of paper. First you make a tube or a cylinder. The cylinder will touch Earth at its fattest part, the equator. The equator is the imaginary line running horizontally around the middle of Earth. The poles are the farthest points from the cylinder. If you shine a light from the inside of your model Earth out to the cylinder, the image projected onto the paper is a Mercator projection. Where does the projection represent Earth best? Where is it worst? Your map would be most correct at the equator. The shapes and sizes of continents become more stretched out near the poles. Early sailors and navigators found the Mercator map useful because most explorations were located near the equator. Many world maps still use the Mercator projection. The Mercator projection is best within 15 degrees north or south of the equator. Landmasses or countries outside that zone get stretched out of shape. The further the feature is from the equator, the more out of shape it is stretched. For example, if you look at Greenland on a globe, you see it is a relatively small country near the North Pole. Yet, on a Mercator projection, Greenland looks almost as big the United States. Because Greenland is closer to the pole, the continents shape and size are greatly increased. The United States is closer to its true dimensions. In a Mercator projection, all compass directions are straight lines. This makes it a good type of map for navigation. The top of the map is north, the bottom is south, the left side is west and the right side is east. However, because it is a flat map of a curved surface, a straight line on the map is not the shortest distance between the two points it connects. |
modeling earths surface | T_0379 | Instead of a cylinder, you could wrap the flat paper into a cone. Conic map projections use a cone shape to better represent regions near the poles (Figure 2.17). Conic projections are best where the cone shape touches the globe. This is along a line of latitude, usually the equator. |
modeling earths surface | T_0380 | What if want to wrap a different approach? Lets say you dont want to wrap a flat piece of paper around a round object? You could put a flat piece of paper right on the area that you want to map. This type of map is called a gnomonic map projection (Figure 2.18). The paper only touches Earth at one point. The sizes and shapes of countries near that point are good. The poles are often mapped this way to avoid distortion. A gnomic projection is best for use over a small area. |
modeling earths surface | T_0381 | In 1963, Arthur Robinson made a map with more accurate sizes and shapes of land areas. He did this using mathematical formulas. The formulas could directly translate coordinates onto the map. This type of projection is shaped like an oval rather than a rectangle (Figure 2.19). Robinsons map is more accurate than a Mercator projection. The shapes and sizes of continents are closer to true. Robinsons map is best within 45 degrees of the equator. Distances along the equator and the lines parallel to it are true. However, the scales along each line of latitude are different. In 1988, the National Geographic Society began to use Robinsons projection for its world maps. Whatever map projection is used, maps help us find places and to be able to get from one place to another. So how do you find your location on a map? |
modeling earths surface | T_0382 | Most maps use a grid of lines to help you to find your location. This grid system is called a geographic coordinate system. Using this system you can define your location by two numbers, latitude and longitude. Both numbers are angles between your location, the center of Earth, and a reference line (Figure 2.20). |
modeling earths surface | T_0383 | Lines of latitude circle around Earth. The equator is a line of latitude right in the middle of the planet. The equator is an equal distance from both the North and South Pole. If you know your latitude, you know how far you are north or south of the equator. |
modeling earths surface | T_0384 | Lines of longitude are circles that go around Earth from pole to pole, like the sections of an orange. Lines of longitude start at the Prime Meridian. The Prime Meridian is a circle that runs north to south and passes through Greenwich, England. Longitude tells you how far you are east or west from the Prime Meridian (Figure 2.21). You can remember latitude and longitude by doing jumping jacks. When your hands are above your head and your feet are together, say longitude (your body is long!). When you put your arms out to the side horizontally, say latitude (your head and arms make a cross, like the t in latitude). While you are jumping, your arms are going the same way as each of these grid lines: horizontal for latitude and vertical for longitude. |
modeling earths surface | T_0385 | If you know the latitude and longitude of a place, you can find it on a map. Simply place one finger on the latitude on the vertical axis of the map. Place your other finger on the longitude along the horizontal axis of the map. Move your fingers along the latitude and longitude lines until they meet. For example, say the location you want to find is at 30o N and 90o W. Place your right finger along 30o N at the right of the map. Place your left finger along the bottom at 90o W. Move your fingers along the lines until they meet. Your location should be near New Orleans, Louisiana, along the Gulf coast of the United States. What if you want to know the latitude and longitude of your location? If you know where you are on a map, point to the place with your fingers. Take one finger and move it along the latitude line to find your latitude. Then move another finger along the longitude line to find your and longitude. |
modeling earths surface | T_0386 | You can also use a polar coordinate system. Your location is marked by an angle and distance from some reference point. The angle is usually the angle between your location, the reference point, and a line pointing north. The distance is given in meters or kilometers. To find your location or to move from place to place, you need a map, a compass, and some way to measure your distance, such as a range finder. Suppose you need to go from your location to a marker that is 20o E and 500 m from your current position. You must do the following: Use the compass and compass rose on the map to orient your map with north. Use the compass to find which direction is 20o E. Walk 500 meters in that direction to reach your destination. Polar coordinates are used in a sport called orienteering. People who do orienteering use a compass and a map with polar coordinates. Participants find their way along a course across wilderness terrain (Figure 2.22). They move to various checkpoints along the course. The winner is the person who completes the course in the fastest time. |
modeling earths surface | T_0387 | Earth is a sphere and so is a globe. A globe is the best way to make a map of the whole Earth. Because both the planet and a globe have curved surfaces, the sizes and shapes of countries are not distorted. Distances are true to scale. (Figure 2.23). Globes usually have a geographic coordinate system and a scale. The shortest distance between two points on a globe is the length of the portion of a circle that connects them. Globes are difficult to make and carry around. They also cannot be enlarged to show the details of any particular area. Globes are best sitting on your desk for reference. Google Earth is a neat site to download to your computer. This is a link that you can follow to get there: http://w tilt your image and lots more. |
topographic maps | T_0388 | Mapping is an important part of Earth Science. Topographic maps use a line, called a contour line, to show different elevations on a map. Contour lines show the location of hills, mountains and valleys. A regular road map shows where a road goes. But a road map doesnt show if the road goes over a mountain pass or through a valley. A topographic map shows you the features the road is going through or past. Lets look at topographic maps. Look at this view of the Swamp Canyon Trail in Bryce Canyon National Park, Utah (Figure 2.25). You can see the rugged canyon walls and valley below. The terrain has many steep cliffs with high and low points between the cliffs. Now look at the same section of the visitors map (Figure 2.26). You can see a green line that is the main road. The black dotted lines are trails. You see some markers for campsites, a picnic area, and a shuttle bus stop. The map does not show the height of the terrain. Where are the hills and valleys located? What is Natural Bridge? How high are the canyon walls? Which way do streams flow? A topographic map represents the elevations in an area (Figure 2.27). We mentioned topographic maps in the section on orienteering above. |
topographic maps | T_0389 | Contour lines connect all the points on the map that have the same elevation. Lets take a closer look at this (Figure Each contour line represents a specific elevation. The contour line connects all the points that are at the same elevation. Every fifth contour line is made bold. The bold contour lines have numbers to show elevation. Contour lines run next to each other and NEVER cross one another. If the lines crossed it would mean that one place had two different elevations. This cannot happen. |
topographic maps | T_0390 | Since each contour line represents a specific elevation, two different contour are separated by the same difference in elevation (e.g. 20 ft or 100 ft.). This difference between contour lines is called the contour interval. You can calculate the contour interval by following these steps: a. Take the difference in elevation between 2 bold lines. b. Divide that difference by the number of contour lines between them. Imagine that the difference between two bold lines is 100 feet and there are five lines between them. What is the contour interval? If you answered 20 feet, then you are correct (100 ft/5 lines = 20 ft between lines). The legend on the map also gives the contour interval. |
topographic maps | T_0391 | How does a topographic map tell you about the terrain? Lets consider the following principles: 1. The spacing of contour lines shows the slope of the land. Contour lines that are close together indicate a steep slope. This is because the elevation changes quickly in a small area. Contour lines that seem to touch indicate a very steep slope, like a cliff. When contour lines are spaced far apart the slope is gentle. So contour lines help us see the three-dimensional shape of the land. Look at the topographic map of Stowe, Vermont (Figure 2.28). There is a steep hill rising just to the right of the city of Stowe. You can tell this because the contour lines there are closely spaced. The contour lines also show that the hill has a sharp rise of about 200 feet. Then the slope becomes less steep toward the right. 2. Concentric circles indicate a hill. Figure 2.29 shows another side of the topographic map of Stowe, Vermont. When contour lines form closed loops, there is a hill. The smallest loops are the higher elevations on the hill. The larger loops encircling the smaller loops are downhill. If you look at the map, you can see Cady Hill in the lower left and another, smaller hill in the upper right. 3. Hatched concentric circles indicate a depression. The hatch marks are short, perpendicular lines inside the circle. The innermost hatched circle represents the deepest part of the depression. The outer hatched circles represent higher elevations (Figure 2.30). 4. V-shaped portions of contour lines indicate stream valleys. The V shape of the contour lines point uphill. There is a V shape because the stream channel passes through the point of the V. The open end of the V represents the downstream portion. A blue line indicates that there is water running through the valley. If there is not a blue line the V pattern indicates which way water flows. In Figure 2.31, you can see examples of V-shaped markings. Try to find the direction a stream flows. 5. Like other maps, topographic maps have a scale so that you can find the horizontal distance. You can use the horizontal scale to calculate the slope of the land (vertical height/horizontal distance). Common scales used in United States Geological Service (USGS) maps include the following: 1:24,000 scale - 1 inch = 2000 ft 1:100,000 scale - 1 inch = 1.6 miles 1:250,000 scale - 1 inch = 4 miles Including contour lines, contour intervals, circles, and V-shapes allows a topographic map to show three-dimensional information on a flat piece of paper. A topographic map gives us a good idea of the shape of the land. |
topographic maps | T_0392 | As we mentioned above, topographic maps show the shape of the land. You can determine a lot of information about the landscape using a topographic map. These maps are invaluable for Earth scientists. |
topographic maps | T_0393 | Earth scientists use topographic maps for many things: Describing and locating surface features, especially geologic features. Determining the slope of the Earths surface. Determining the direction of flow for surface water, groundwater, and mudslides. Hikers, campers, and even soldiers use topographic maps to locate their positions in the field. Civil engineers use topographic maps to determine where roads, tunnels, and bridges should go. Land use planners and architects use topographic maps when planning development projects, such as housing projects, shopping malls, and roads. |
topographic maps | T_0394 | Oceanographers use a type of topographic map that shows water depths (Figure 2.32). On this map, the contour lines represent depth below the surface. Therefore, high numbers are deeper depths and low numbers are shallow depths. These maps are made from depth soundings or sonar data. They help oceanographers understand the shape of bottoms of lakes, bays, and the ocean. This information also helps boaters navigate safely. |
topographic maps | T_0395 | A geologic map shows the different rocks that are exposed at the surface of a region. Rock units are shown in a color identified in a key. On the geologic map of the Grand Canyon, for example, different rock types are shown in different colors. Some people call the Grand Canyon layer cake geology because most of the rock units are in layers. Rock units show up on both sides of a stream valley. A geologic map looks very complicated in a region where rock layers have been folded, like the patterns in marble cake. Faults are seen on this geologic map cutting across rock layers. When rock layers are tilted, you will see stripes of each layer on the map. There are symbols on a geologic map that tell you which direction the rock layers slant, and often there is a cut away diagram, called a cross section, that shows what the rock layers look like below the surface. A large-scale geologic map will just show geologic provinces. They do not show the detail of individual rock layers. |
using satellites and computers | T_0396 | To understand what satellites can do, lets look at an example. One of the deadliest hurricanes in United States history hit Galveston, Texas in 1900. The storm was first spotted at sea on Monday, August 27th , 1900. It was a tropical storm when it hit Cuba on September 3rd . By September 8th , it had intensified to a hurricane over the Gulf of Mexico. It came ashore at Galveston (Figure 2.34). Because there was not advanced warning, more than 8000 people lost their lives. Today, we have satellites with many different types of instruments that orbit the Earth. With these satellites, satellites can see hurricanes form at sea. They can follow hurricanes as they move from far out in the oceans to shore. Weather forecasters can warn people who live along the coasts. These advanced warning give people time to prepare for the storm. They can find a safe place or even evacuate the area, which helps save lives. |
using satellites and computers | T_0397 | Satellites orbit high above the Earth in several ways. Different orbits are important for viewing different things about the planet. |
using satellites and computers | T_0398 | A satellite in a geostationary orbit flies above the planet at a distance of 36,000 km. It takes 24 hours to complete one orbit. The satellite and the Earth both complete one rotation in 24 hours. This means that the satellite stays over the same spot. Weather satellites use this type of orbit to observe changing weather conditions over a region. Communications satellites, like satellite TV, use this type of orbit to keep communications going full time. |
using satellites and computers | T_0399 | Another useful orbit is the polar orbit (Figure 2.35). The satellite orbits at a distance of several hundred kilometers. It makes one complete orbit around the Earth from the North Pole to the South Pole about every 90 minutes. In this same amount of time, the Earth rotates only slightly underneath the satellite. So in less than a day, the satellite can see the entire surface of the Earth. Some weather satellites use a polar orbit to see how the weather is changing globally. Also, some satellites that observe the land and oceans use a polar orbit. |
using satellites and computers | T_0400 | The National Aeronautics and Space Administration (NASA) has launched a fleet of satellites to study the Earth (Figure 2.36). The satellites are operated by several government agencies, including NASA, the National Oceano- graphic and Atmospheric Administration (NOAA), and the United States Geological Survey (USGS). By using different types of scientific instruments, satellites make many kinds of measurements of the Earth. Some satellites measure the temperatures of the land and oceans. Some record amounts of gases in the atmosphere, such as water vapor and carbon dioxide. Some measure their height above the oceans very precisely. From this information, they can measure sea level. Some measure the ability of the surface to reflect various colors of light. This information tells us about plant life. Some examples of the images from these types of satellites are shown in Figure 2.37. |
using satellites and computers | T_0401 | In order to locate your position on a map, you must know your latitude and your longitude. But you need several instruments to measure latitude and longitude. What if you could do the same thing with only one instrument? Satellites can also help you locate your position on the Earths surface. By 1993, the United States military had launched 24 satellites to help soldiers locate their positions on battlefields. This system of satellites was called the Global Positioning System (GPS). Later, the United States government allowed the public to use this system. Heres how it works. You must have a GPS receiver to use the system (Figure 2.38). You can buy many types of these in stores. The |
using satellites and computers | T_0402 | Prior to the late 20th and early 21st centuries, mapmakers sent people out in the field to determine the boundaries and locations for various features for maps. State or county borders were used to mark geological features. Today, people in the field use GPS receivers to mark the locations of features. Map-makers also use various satellite images and computers to draw maps. Computers are able to break apart the fine details of a satellite image, store the pieces of information, and put them back together to make a map. In some instances, computers can make 3-D images of the map and even animate them. For example, scientists used computers and satellite images from Mars to create a 3-D image of Mars ice cap (Figure 2.39). The image makes you feel as if you are looking at the ice cap from the surface of Mars. When you link any type of information to a location, you can put together incredibly useful maps and images. The information could be numbers of people living in an area, types of plants or soil, locations of groundwater or levels of rainfall. As long as you can link the information to a position with a GPS receiver, you can store it in a computer for later processing and map-making. This type of mapping is called a Geographic Information System (GIS). Geologists can use GIS to make maps of natural resources. City leaders might link these resources to where people live and help plan the growth of cities or communities. Other types of data can be linked by GIS. For example, Figure 2.40 shows a map of the counties where farmers made insurance claims for crop damage in 2008. Computers have improved how maps are made. They have also increased the amount of information that can be displayed. During the 21st century, computers will be used more and more in mapping. |
using satellites and computers | T_0403 | 5. What would have happened if there had been satellites during the time of the 1900 Galveston earthquake? 6. What would have happened if there had been no satellites when hurricane Katrina struck the Gulf of Mexico coast in 2005? |
use and conservation of resources | T_0404 | We need natural resources for just about everything we do. We need them for food and clothing, for building materials and energy. We even need them to have fun. Table 20.1 gives examples of how we use natural resources. Can you think of other ways we use natural resources? Use Vehicles Resources Rubber for tires from rubber trees Steel frames and other metal parts from minerals such as iron Example iron ore Use Electronics Resources Plastic cases from petroleum prod- ucts Glass screens from minerals such as lead Example lead ore Homes Nails from minerals such as iron Timber from trees spruce timber Jewelry Gemstones such as diamonds Minerals such as silver silver ore Food Sunlight, water, and soil Minerals such as phosphorus corn seeds in soil Clothing Wool from sheep Cotton from cotton plants cotton plants Recreation Water for boating and swimming Forests for hiking and camping pine forest Some natural resources are renewable. Others are not. It depends in part on how we use them. |
use and conservation of resources | T_0405 | Renewable resources can be renewed as they are used. An example is timber, which comes from trees. New trees can be planted to replace those that are cut down. Sunlight is a renewable resource. It seems we will never run out of that! Just because a resource is renewable, it doesnt mean we should use it carelessly. If we arent careful, we can pollute resources. Then they may no longer be fit for use. Water is one example. If we pollute a water source it may not be usable for drinking, bathing or any other type of use. We can also overuse resources that should be renewable. In this case the resources may not be able to recover. For example, fish are renewable resources. Thats because they can reproduce and make more fish. But water pollution and overfishing can cause them to die out if their population becomes too low. Figure 20.1 shows another example. |
use and conservation of resources | T_0406 | Some resources cant be renewed. At least, they cant be renewed fast enough to keep up with use. Fossil fuels are examples. It takes millions of years for them to form. We are using them up much more quickly. Elements that are used to produce nuclear power are other examples. They include uranium. This element is already rare. Sooner or later, it will run out. Supplies of non-renewable resources are shrinking. This makes them harder to get. Oil is a good example. Oil reserves beneath land are running out. So oil companies have started to drill for oil far out in the ocean. This costs more money. Its also more dangerous. Figure 20.2 shows an oil rig that exploded in 2010. The explosion killed 11 people. Millions of barrels of oil spilled into the water. It took months to plug the leak. |
use and conservation of resources | T_0407 | Rich nations use more natural resources than poor nations. In fact, the richest 20 percent of people use 85 percent of the worlds resources. What about the poorest 20 percent of people? They use only 1 percent of the worlds resources. You can see this unequal distribution of oil resources in Figure 20.3. Imagine a world in which everybody had equal access to resources. Some people would have fewer resources than they do now. But many people would have more. In the real world, the difference between rich and poor just keeps growing. |
use and conservation of resources | T_0408 | Every 20 minutes, the human population adds 3,500 more people. More people need more resources. For example, we now use five times more fossil fuels than we did in 1970. The human population is expected to increase for at least 40 years. What will happen to resource use? |
use and conservation of resources | T_0409 | How can we protect Earths natural resources? One answer is conservation. This means saving resources. We need to save resources so some will be left for the future. We also need to protect resources from pollution and overuse. When we conserve resources, we also cut down on the trash we produce. Americans throw out 340 million tons of trash each year. We throw out 2.5 million plastic bottles alone every hour! Most of what we throw out ends up in landfills. You can see a landfill in Figure 20.4. In a landfill, all those plastic bottles take hundreds of years to break down. What are the problems caused by producing so much trash? Natural resources must be used to produce the materials. Land must be given over to dump the materials. If the materials are toxic, they may cause pollution. |
use and conservation of resources | T_0410 | You probably already know about the three Rs. They stand for reduce, reuse, and recycle. The third R recycle has caught on in a big way. Thats because its easy. There are thousands of places to drop off items such as aluminum cans for recycling. Many cities allow you to just put your recycling in a special can and put it at the curb. We havent done as well with the first two Rs reducing and reusing. But they arent always as easy as recycling. Recycling is better than making things from brand new materials. But it still takes some resources to turn recycled items into new ones. It takes no resources at all to reuse items or not buy them in the first place. |
use and conservation of resources | T_0411 | Reducing resource use means just what it says using fewer resources. There are lots of ways to reduce our use of resources. Buy durable goods. Choose items that are well made so they will last longer. Youll buy fewer items in the long run, so youll save money as well as resources. Thats a win-win! Repair rather than replace. Fix your bike rather than buying a new one. Sew on a button instead of buying a new shirt. Youll use fewer resources and save money. Buy only what you need. Dont buy a gallon of milk if you can only drink half of it before it spoils. Instead, buy a half gallon and drink all of it. You wont be wasting resources (or money!). Buy local. For example, buy local produce at a farmers market, like the one in Figure 20.5. A lot of resources are saved by not shipping goods long distances. Products bought at farmers markets use less packaging, too! About a third of what we throw out is packaging. Try to buy items with the least amount of packaging. For example, buy bulk items instead of those that are individually wrapped. Also, try to select items with packaging that can be reused or recycled. This is called precycling. Pop cans and plastic water bottles, for example, are fairly easy to recycle. Some types of packaging are harder to recycle. You can see examples in Figure 20.6. If it cant be reused or recycled, its a waste of resources. Many plastics: The recycling symbol on the bottom of plastic containers shows the type of plastic they contain. Numbers 1 and 2 are easier to recycle than higher numbers. Mixed materials: Packaging that contains more than one material may be hard to recycle. This carton is made mostly of cardboard. But it has plastic around the opening. |
use and conservation of resources | T_0412 | Reusing resources means using items again instead of throwing them away. A reused item can be used in the same way by someone else. Or it can be used in a new way. For example, Shana has a pair of jeans she has outgrown. She might give them to her younger sister to wear. Or she might use them to make something different for herself, say, a denim shoulder bag. Some other ideas for reusing resources are shown in Figure 20.7. |
use and conservation of resources | T_0413 | Many things can be recycled. The materials in them can be reused in new products. For example, plastic water bottles can be recycled. The recycled material can be made into t-shirts! Old phone books can also be recycled and made into textbooks. When you shop for new products, look for those that are made of recycled materials (see Figure 20.8). Even food scraps and lawn waste can be recycled. They can be composted and turned into humus for the garden. At most recycling centers, you can drop off metal cans, cardboard and paper products, glass containers, and plastic bottles. Recycling stations like the one in Figure 20.9 are common. Curbside recycling usually takes these items too. Do you know how to recycle in your community? Contact your local solid waste authority to find out. If you dont already recycle, start today. Its a big way you can help the planet! |
use and conservation of energy | T_0414 | Think about your typical day. How do you use energy? Do you take a shower when you first get out of bed? What about taking a shower uses energy? It takes energy to heat the water and to pump the water to your home. Do you eat a hot breakfast? Energy is used to cook your food. Do you ride a bus or have someone drive you to school? Motor vehicles need energy from fossil fuels to run. |
use and conservation of energy | T_0415 | Figure 20.10 shows the major ways energy is used in the U.S. A lot of energy is used in homes. In fact, more energy is used in homes than in stores and businesses. Even more energy is used for transportation. A lot of fuel is necessary to move people and goods around the country. Industry uses the most energy. Industrial uses account for one-third of all the energy used in the U.S. |
use and conservation of energy | T_0416 | Figure 20.11 shows the energy resources used in the U.S. The U.S. depends mainly on fossil fuels. Petroleum is used more than any other resource. Renewable energy resources, such as solar and wind energy, could provide all the energy we need, but they are not yet widely used in the U.S. |
use and conservation of energy | T_0417 | We must use energy to get energy resources. This is true of non-renewable and renewable energy. Getting fossil fuels so that they can be used takes many steps. All of these steps use energy. 1. 2. 3. 4. 5. Fossil fuels must be found. The resources must be removed from the ground. These resources need to be refined, some more than others. Fossil fuels may need to be changed to a different form of energy. Energy resources must be transported from where they are produced to where they are sold or used. Consider petroleum as an example. Oil companies explore for petroleum in areas where they think it might be. When they find it, they must determine how much is there. They must also know how hard it will be to get. If theres enough to make it worthwhile, they will decide to go for it. To extract petroleum, companies they must build huge rigs, like the one in Figure 20.12. An oil rig drills deep into the ground and pumps the oil to the surface. The oil is then transported to a refinery. At the refinery, the oil is heated. It will then separate into different products, such as gasoline and motor oil. Finally, the oil products are transported to gas stations, stores, and industries. At every step, energy is used. For every five barrels of oil we use, it takes at least one barrel to get the oil. Less energy is needed to get renewable energy sources. Solar energy is a good example. Sunlight is everywhere, so no one needs to go out and find it. We dont have to drill for it or pump it to the surface. We just need to install solar panels like the ones in Figure 20.13 and let sunlight strike them. The energy from the sunlight is changed to electricity. The electricity is used to power lights and appliances in the house. So solar energy doesnt have to be transported. |
use and conservation of energy | T_0418 | Nonrenewable energy resources will run out before long. Using these energy resources also produces pollution and increases global warming. For all these reasons, we need to use less of these energy sources. We also need to use them more efficiently. |
use and conservation of energy | T_0419 | There are many ways to use less energy. Table 20.2 lists some of them. Can you think of other ways to use less energy? For example, how might schools use less energy? Use of Energy Transportation How to Use Less Plan ahead to reduce the number of trips you make. Take a bus or train instead of driving. Walk or bike rather than ride. Home Unplug appliances when not in use. Turn off lights when you leave a room. Put on a sweater instead of turning up the heat. Run the dishwasher and washing machine only when full. |
use and conservation of energy | T_0420 | We can get more work out of the energy we use. Table 20.3 show some ways to use energy more efficiently. By getting more bang for the buck, we wont need to use as much energy overall. Does your family use energy efficiently? How could you find out? Use of Energy More Efficient Use Another way to use energy more efficiently is with Energy Star appliances. They carry the Energy Star logo, shown in Figure 20.14. To be certified as Energy Star, the appliance must use less energy. Energy Star appliances save a lot of energy over their lifetime. What if millions of households used Energy Star appliances? How much energy would it save? |
humans and the water supply | T_0421 | Figure 21.1 shows how people use water worldwide. The greatest use is for agriculture and then industry. Municipal use is last, but is also important. Municipal use refers to water used by homes and businesses in communities. |
humans and the water supply | T_0422 | Many crops are grown where there isnt enough rainfall for plants to thrive. For example, crops are grown in deserts of the American southwest. How is this possible? The answer is irrigation. Irrigation is any way of providing extra water to plants. Most of the water used in agriculture is used for irrigation. Livestock also use water, but they use much less. Irrigation can waste a lot of water. The type of irrigation shown in Figure 21.2 is the most wasteful. The water is sprayed into the air and then falls to the ground. But much of the water never reaches the crops. Instead, it evaporates in the air or runs off the fields. Irrigation water may cause other problems. The water may dissolve agricultural chemicals such as pesticides. When the water soaks into the ground, the dissolved chemicals do, too. They may enter groundwater or run off into rivers or lakes. Salts in irrigation water can also collect in the soil. The soil may get too salty for plants to grow. |
humans and the water supply | T_0423 | Almost a quarter of the water used worldwide is used in industry. Industries use water for many purposes. Chemical processes need a lot of water. Water is used to generate electricity. An important way that industries use water is to cool machines and power plants. |
humans and the water supply | T_0424 | Think about all the ways people use water at home. Besides drinking it, they use it for cooking, bathing, washing dishes, doing laundry, and flushing toilets. The water used inside homes goes down the drain. From there it usually ends up in a sewer system. At the sewage treatment plant, water can be is treated and prepared for reuse. Households may also use water outdoors. If your family has a lawn or garden, you may water them with a hose or sprinkler. You probably use water to wash the car, like the teen in Figure 21.3. Much of the water used outdoors evaporates or runs off into the gutter. The runoff water may end up in storm sewers that flow into a body of water, such as the ocean. |
humans and the water supply | T_0425 | There are many ways to use water for fun, from white water rafting to snorkeling. When you do these activities you dont actually use water. You are doing the activity on or in the water. What do you think is the single biggest use of water for fun? Believe it or not, its golf! Keeping golf courses green uses an incredible amount of water. Since many golf courses are in sunny areas, much of the water is irrigation water. Many golf courses, like the one in Figure 21.4, have sprinkler systems. Like any similar sprinkler system, much of this water is wasted. It evaporates or runs off the ground. |
humans and the water supply | T_0426 | Most Americans have plenty of fresh, clean water. But many people around the world do not. In fact, water scarcity is the worlds most serious resource problem. How can that be? Water is almost everywhere. More than 70 percent of Earths surface is covered by water. |
humans and the water supply | T_0427 | One problem is that only a tiny fraction of Earths water is fresh, liquid water that people can use. More than 97 percent of Earths water is salt water in the oceans. Just 3 percent is freshwater. Most of the freshwater is frozen in ice sheets, icebergs, and glaciers (see Figure 21.5). |
humans and the water supply | T_0428 | Rainfall varies around the globe. About 40 percent of the land gets very little rain. About the same percentage of the worlds people dont have enough water. You can compare global rainfall with the worldwide freshwater supply at the two URLs below. Drier climates generally have less water for people to use. In some places, people may have less water available to them for an entire year than many Americans use in a single day! How much water is there where you live? Global rainfall: http://commons.wikimedia.org/wiki/File:World_precip_annual.png Freshwater supply: http://commons.wikimedia.org/wiki/File:2006_Global_Water_Availability.svg |
humans and the water supply | T_0429 | Richer nations can drill deep wells, build large dams or supply people with water in other ways. In these countries, just about everyone has access to clean running water in their homes. Its no surprise that people in these countries also use the most water. In poorer nations, there is little money to develop water supplies. Look at the people in Figure 21.6. These people must carry water home in a bucket from a distant pump. |
humans and the water supply | T_0430 | Water shortages are common in much of the world. People are most likely to run short of water during droughts. A drought is a period of unusually low rainfall. Human actions have increased how often droughts occur. One way people can help to bring on drought is by cutting down trees. Trees add a lot of water vapor to the air. With fewer trees, the air is drier and droughts are more common. We already use six times as much water today as we did a hundred years ago. As the number of people rises, our need for water will grow. By the year 2025, only half the worlds people will have enough clean water. Water is such a vital resource that serious water shortages may cause other problems. Crops and livestock may die, so people will have less food available. Other uses of water, such as industry, may have to stop. This reduces the jobs people can get and the products they can buy. People and nations may fight over water resources. In extreme cases, people may die from lack of water. The Figure 21.7 shows the global water situation in the 2030s with water stress and water scarcity on the map. |
humans and the water supply | T_0431 | The water Americans get from their faucets is generally safe. This water has been treated and purified. But at least 20 percent of the worlds people do not have clean drinking water. Their only choice may be to drink water straight from a river (see Figure 21.8). If the river is polluted with wastes, it will contain bacteria and other organisms that cause disease. Almost 9 out of 10 cases of disease worldwide are caused by unsafe drinking water. Diseases from unsafe drinking water are the leading cause of death in young children. |
water pollution | T_0432 | Pollution that enters water at just one point is called point source pollution. For example, chemicals from a factory might empty into a stream through a pipe or set of pipes (see Figure 21.9). Pollution that enters in many places is called non-point source pollution. This means that the pollution is from multiple sources. With non-point source pollution, runoff may carry the pollution into a body of water. Which type of pollution do you think is harder to control? |
water pollution | T_0433 | There are three main sources of water pollution: 1. Agriculture. 2. Industry. 3. Municipal, or community, sources. |
water pollution | T_0434 | Huge amounts of chemicals, such as fertilizers and pesticides, are applied to farm fields (see Figure 21.10). Some of the chemicals are picked up by rainwater. Runoff then carries the chemicals to nearby rivers or lakes. Dissolved fertilizer causes too much growth of water plants and algae. This can lead to dead zones where nothing can live in lakes and at the mouths of rivers. Some of the chemicals can infiltrate into groundwater. The contaminated water comes up in water wells. If people drink the polluted water, they may get sick. Waste from livestock can also pollute water. The waste contains bacteria and other organisms that cause disease. In fact, more than 40 human diseases can be caused by water polluted with animal waste. Many farms in the U.S. have thousands of animals. These farms produce millions of gallons of waste. The waste is stored in huge lagoons, like the one in Figure 21.11. Unfortunately, many leaks from these lagoons have occurred. Two examples are described below. In North Carolina, 25 million gallons of hog manure spilled into a nearby river. The contaminated water killed |
water pollution | T_0435 | Factories and power plants may pollute water with harmful substances. Many industries produce toxic chemicals. Some of the worst are arsenic, lead, and mercury. Nuclear power plants produce radioactive chemicals. They cause cancer and other serious health problems. Oil tanks and pipelines can leak. Leaks may not be noticed until a lot of oil has soaked into the ground. The oil may pollute groundwater so it is no longer fit to drink. |
water pollution | T_0436 | Municipal refers to the community. Households and businesses in a community are also responsible for polluting the water supply. For example: People apply chemicals to their lawns. The chemicals may be picked up by rainwater. The contaminated runoff enters storm sewers and ends up in nearby rivers or lakes. Underground septic tanks can develop leaks. This lets household sewage seep into groundwater. Municipal sewage treatment plants dump treated wastewater into rivers or lakes. Sometimes the wastewater is not treated enough and contains bacteria or toxic chemicals. |
water pollution | T_0437 | The oceans are vast. You might think they are too big to be harmed by pollution. But thats not the case. Ocean water is becoming seriously polluted. |
water pollution | T_0438 | The oceans are most polluted along coasts. Why do you think thats the case? Of course, its because most pollution enters the oceans from the land. Runoff and rivers carry the majority of pollution into the ocean. Many cities dump their wastewater directly into coastal waters. In some parts of the world, raw sewage and trash may be thrown into the water (see Figure 21.12). Coastal water may become so polluted that people get sick if they swim in it or eat seafood from it. The polluted water may also kill fish and other ocean life. |
water pollution | T_0439 | Oil spills are another source of ocean pollution. To get at oil buried beneath the seafloor, oil rigs are built in the oceans. These rigs pump oil from beneath the ocean floor. Huge ocean tankers carry oil around the world. If something goes wrong with a rig on a tanker, millions of barrels of oil may end up in the water. The oil may coat and kill ocean animals. Some of the oil will wash ashore. This oil may destroy coastal wetlands and ruin beaches. Figure 21.13 shows an oil spill on a beach. The oil washed ashore after a deadly oil rig explosion in the Gulf of Mexico in 2010. |
water pollution | T_0440 | Thermal pollution is pollution that raises the temperature of water. This is caused by power plants and factories that use the water to cool their machines. The plants pump cold water from a lake or coastal area through giant cooling towers, like those in Figure 21.14. As it flows through the towers, the cold water absorbs heat. This warmed water is returned to the lake or sea. Thermal pollution can kill fish and other water life. Its not just the warm temperature that kills them. Warm water cant hold as much oxygen as cool water. If the water gets too warm, there may not be enough oxygen for living things. |
protecting the water supply | T_0441 | In the mid 1900s, people were startled to see the Cuyahoga River in Cleveland, Ohio, burst into flames! The river was so polluted with oil and other industrial wastes that it was flammable. Nothing could live in it. You can see the Cuyahoga River in Figure 21.16 |
protecting the water supply | T_0442 | Disasters such as rivers burning led to new U.S. laws to protect the water. For example, the Environmental Protection Agency (EPA) was established, and the Clean Water Act was passed. Now, water is routinely tested. Pollution is tracked to its source, and polluters are forced to fix the problem and clean up the pollution. They are also fined. These consequences have led industries, agriculture, and communities to pollute the water much less than before. |
protecting the water supply | T_0443 | Most water pollution comes from industry, agriculture, and municipal sources. Homes are part of the municipal source and the individuals and families that live in them can pollute the water supply. What can you do to reduce water pollution? Read the tips below. Properly dispose of motor oil and household chemicals. Never pour them down the drain. Also, dont let them spill on the ground. This keeps them out of storm sewers and bodies of water. Use fewer lawn and garden chemicals. Use natural products instead. For example, use compost instead of fertilizer. Or grow plants that can thrive on their own without any extra help. Repair engine oil leaks right away. A steady drip of oil from an engine can quickly add up to gallons. When the oil washes off driveways and streets it can end up in storm drains and pollute the water supply. Dont let pet litter or pet wastes get into the water supply (see Figure 21.17). The nitrogen they contain can cause overgrowth of algae. The wastes may also contain bacteria and other causes of disease. |
protecting the water supply | T_0444 | Water treatment is a series of processes that remove unwanted substances from water. The goal of water treatment is to make the water safe to return to the natural environment or to the human water supply. Treating water for other purposes may not include all the same steps. Thats because water used in agriculture or industry may not have to be as clean as drinking water. You can see how water for drinking is treated in Figure 21.18. Treating drinking water requires at least four processes: 1. Chemicals are added to untreated water. They cause solids in the water to clump together. This is called coagulation. 2. The water is moved to tanks. The clumped solids sink to the bottom of the water. This is called sedimentation. 3. The water is passed through filters that remove smaller particles from the water. This is called filtration. 4. Chlorine is added to the water to kill bacteria and other microbes. This is called disinfection. Finally, the water is pure enough to drink. |
protecting the water supply | T_0445 | Conserving water means using less of it. Of course, this mostly applies to people in the wealthy nations that have the most water and also waste the most. |
protecting the water supply | T_0446 | Irrigation is the single biggest use of water. Overhead irrigation wastes a lot of water. Drip irrigation wastes a lot less. Figure 21.19 shows a drip irrigation system. Water pipes run over the surface of the ground. Tiny holes in the pipes are placed close to each plant. Water slowly drips out of the holes and soaks into the soil around the plants. Very little of the water evaporates or runs off the ground. |
protecting the water supply | T_0447 | Some communities save water with rationing. Much rationing takes place only during times of drought. During rationing, water may not be used for certain things. For example, communities may ban lawn watering and car washing. People may be fined if they use water in these ways. You can do your part. Follow any bans where you live. |
protecting the water supply | T_0448 | Its easy to save water at home. If you save even a few gallons a day you can make a big difference over the long run. The best place to start saving water is in the bathroom. Toilet flushing is the single biggest use of water in the home. Showers and baths are the next biggest use. Follow the tips below to save water at home. Install water-saving toilets. They use only about half as much water per flush. A single household can save up to 20,000 gallons a year with this change alone! Take shorter showers. You can get just as clean in 5 minutes as you can in 10. And youll save up to 50 gallons of water each time you shower. Thats thousands of gallons each year. Use low-flow shower heads. They use about half as much water as regular shower heads. They save thousands of gallons of water. Fix leaky shower heads and faucets. All those drips really add up. At one drip per second, more than 6,000 gallons go down the drain in a year per faucet! Dont leave the water running while you brush your teeth. You could save as much as 10 gallons each time you brush. That could add up to 10,000 gallons in a year. Landscape your home with plants that need little water. This could result in a huge savings in water use. Look at the garden in Figure 21.20. It shows that you dont have to sacrifice beauty to save water. |
air pollution | T_0452 | Air quality is a measure of the pollutants in the air. More pollutants mean poorer air quality. Air quality, in turn, depends on many factors. Some natural processes add pollutants to the air. For example, forest fires and volcanoes add carbon dioxide and soot. In dry areas, the air often contains dust. However, human actions cause the most air pollution. The single biggest cause is fossil fuel burning. |