570

How AreCotton & Cookies

Connected?

How AreCotton & Cookies

Connected?

Joseph Sohm/ChromoSohm, Inc./CORBIS

UO6_MSS05ges 8/20/04 1:37 PM Page 570

In the 1800s, the economy of the South depended heavily on cotton andtobacco—two crops that rob the soil of nutrients, especially nitrogen. By the

late 1800s, the soil was in poor shape. A scientist named George WashingtonCarver set out to change that. He promoted the technique of crop rotation—alternating soil-depleting crops such as cotton with soil-enriching crops such aspeanuts. Many farmers listened to Carver and began planting peanuts. However,there was little market for the crop. So Carver poured his energy into developinguses for peanuts. Ultimately, he came up with more than 300 products madefrom peanuts—everything from soap to axle grease. He also created the firstrecipe for peanut butter cookies, which have become an American favorite.

Visit to find project ideas and resources.Projects include:• History Investigate land use in the U.S. during the past 200 years. Design flip

charts to compare, and then predict, the land use of the future.• Technology Research how legumes “fix” nitrogen and why crop rotation

keeps farm land more productive.• Model Explore peanut inventions. Design your own creative use for peanuts,

write directions, and build a prototype for a class peanut invention fair.Recycling Plastics explores the seven classes of plastics and theiruses, as well as the chemistry of plastic. Discover what it takes torecycle plastic, glass, paper, and aluminum.

earth.msscience.com/unit_project

(background)Joseph Sohm/ChromoSohm, Inc./CORBIS, (c)Andrew A. Wagner

UO6_MSS05ges 8/20/04 1:37 PM Page 571

sections

1 Population Impact on theEnvironment

2 Using LandLab What to wear?

3 Conserving ResourcesLab A World Full of People

Virtual Lab How muchlandfill space can be savedeach year by recycling?

How many peoplelive on your street?There are a lot of people on Earth and moreare added every second. Each person usesland for food, shelter, transportation, andwaste disposal. Fortunately, scientists andcommunity leaders are discovering manyways to protect the land we live on.

Write three ways you can reducethe amount of trash you throw in the garbage.Science Journal

Our Impacton Land

George D. Lepp/Photo Researchers

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573573

1. On a piece of paper, draw a square that is10 cm on each side. This square represents1 km2 of land.

2. In 1965, an average of 22 people lived on1 km2 of land. Draw 22 small circles insideyour square to represent this.

3. In 1990, the average was 35. Add 13 cir-cles to illustrate this increase.

4. In 2025, the estimated number of peoplewill be 52. Add enough circles to repre-sent this increase.

5. Prepare a bar graph that shows popula-tion density for these years.

6. Think Critically Use your bar graph toexplain how Earth’s human populationhas changed over time.

What happens as the humanpopulation grows?You’re the first one on the school bus in themorning. After a few more stops, you noticethat the bus is rather noisy. By the time youget to school, every seat is taken. Like theschool bus, space on Earth is limited.

Start-Up Activities

Preview this chapter’s contentand activities atearth.msscience.com

How Human Acivities ImpactLand Make the followingFoldable to help identify what

you know, what you want to know, and whatyou learned about how humans impact land.

Fold a verticalsheet of paper fromside to side. Makethe front edgeabout 1.25 cmshorter than theback edge.

Turn lengthwiseand fold intothirds.

Unfold and cut only the top layeralong both folds to make three tabs.Label each tab as shown.

Identify Questions Before you read the chapter,write what you already know about the impact ofhuman activities on land under the left tab of yourFoldable, and write questions about what you’dlike to know under the center tab. As you read thechapter, list what you learned under the right tab.

STEP 3

STEP 2

STEP 1

Know? Learned?Like to know?

George D. Lepp/Photo Researchers

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574 CHAPTER 20 Our Impact on Land

Population and Carrying Capacity Look around and identify the kinds of living things you see.

You might see students, fish in an aquarium, or squirrels in thetrees. Perhaps plants are on the windowsill. These are examplesof populations. A population is all of the individuals of onespecies occupying a particular area. As you can see in Figure 1,the area can be small or large. For example, a human popula-tion can be of one community, such as Los Angeles, or theentire planet.

Earth’s Increasing Population Do you ever wonder howmany people live on Earth? The global population in 2000 was6.1 billion. Each day, the number of humans increases byapproximately 200,000. Earth is now experiencing a populationexplosion. The word explosion is used because the rate at whichthe population is growing has increased rapidly in recent history.

Why is the increasing number of humans onEarth called a population explosion?

Population Impact onthe Environment

■ Describe how fast the humanpopulation is increasing.

■ Identify reasons for Earth’s rapidincrease in human population.

■ List several ways each personcan affect the environment.

As the human population grows,resources are depleted and morewaste is produced.

Review Vocabularynatural resource: materials sup-plied by nature that are necessaryor useful for life

New Vocabulary

• population

• carrying capacity

• pollutant

Figure 1 A population is thenumber of individuals occupyingan area. The population ofCranford includes the populationof the classroom.

(inset)Joseph Sohm; ChromoSohm Inc./CORBIS, (r)Bob Daemmrich/Stock Boston

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SECTION 1 Population Impact on the Environment 575

Population Growth Many years ago, few people lived onEarth. You can see in Figure 2 that it took thousands of years forthe population to reach one billion people. After the mid 1800’s,the population increased much faster. The human population hasincreased because modern medicine, clean water, and betternutrition have decreased the death rate. This means that morepeople are living longer. In addition, the number of births hasincreased because more people survive to the age at which theycan have children.

By 2050, the population is predicted to be about 9 billion—one and a half times what it is now. Imagine the effect such alarge human population will have on the environment. Will thethings that have helped the population grow, such as improvedhealth care, agriculture, and clean water, be maintainable? WillEarth have enough natural resources to support such a largepopulation?

Population Limits Each person uses space and resources.Population size depends on the amount of available resourcesand how members of the population use them. If resourcesbecome scarce or if the environment is damaged, members ofthe population can suffer and population size could decrease.

People once thought that Earth had an endless supply ofresources such as fossil fuels, metals, rich soils, and clean water. It’snow known that this isn’t true. Earth’s resources are limited. Theplanet has a carrying capacity. Carrying capacity is the largestnumber of individuals of a particular species that the environmentcan support. Unless Earth’s resources are treated with care, theycould disappear and the human population might reach its carry-ing capacity.

Figure 2 Human populationgrowth remained relatively steadyuntil the beginning of the nine-teenth century. The growth ratethen began to increase rapidly.Infer why the human populationhas experienced a sharp increase ingrowth rate since 1800.

Population Growth of Modern Humans

4

6

2

0

8

10

3

5

1

7

9

Year

Hu

man

pop

ula

tion

(bill

ion

s)

100,000(years ago)

1700 A.D. 1800 A.D. 1900 A.D. 2000 A.D. 2100 A.D.

9.1 billion2050

6.1 billion2000

1 billion1810

3 billion1960

600 million1700

Topic: Human PopulationVisit for Weblinks to information aboutpopulation updates.

Activity Compare the rate ofpeople added every 30 seconds inthe U.S. to the global rate.

earth.msscience.com

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576 CHAPTER 20 Our Impact on Land

People and the EnvironmentHow will you affect the environment over your lifetime? By the

time you’re 75 years old, you will have produced enough garbageto equal the mass of eleven African elephants (53,000 kg).You will have consumed enough water to fill 68,000 bathtubs(18 million L). If you live in the United States, you will have usedseveral times as much energy as an average person living elsewherein the world.

Daily Activities Every day you affect the environment. Theelectricity you use might be generated by burning fossil fuels.The environment changes when fuels are mined, and again laterwhen they are burned. The water that you use must be treatedto make it as clean as possible before being returned to the envi-ronment. You eat food, which needs soil to grow. Much of thefood you eat is grown using chemical substances, such as pesti-cides and herbicides, to kill insects and weeds. These chemicalscan get into water supplies and threaten the health of livingthings if the chemicals become too concentrated. How else doyou and other people affect the environment?

As you can see in Figure 3, many of the products you use aremade of plastic and paper. Plastic begins as oil. The process ofrefining oil can produce pollutants—substances that contami-nate the environment. In the process of changing trees to paper,several things happen that impact the environment. Trees are cutdown. Oil is used to transport the trees to the paper mill, andwater and air pollutants are given off in the papermaking process.

How do the products you use affect theenvironment?

Figure 3 You use manyresources every day. State what resources were con-sumed to produce items such asthose shown in the photo.

Pesticides Bald eaglesare fish-eating birdswhose population in theUnited States declinedrapidly during the 1950sand early 1960s. One ofthe reasons this occurredwas the use of pesticides,which affected reproduc-tion. Researchers whostudy how pesticidesapplied to land can endup in an eagle’s bodyinclude biologists,chemists, mathemati-cians, and toxicologists.

Timothy Fuller

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SECTION 1 Population Impact on the Environment 577

Self Check1. Use Graphs Using Figure 2, estimate the human

population increase from 1800 to 1960.

2. State three reasons why the human population isincreasing rapidly.

3. Infer what might happen if the human populationreaches its carrying capacity.

4. Think Critically How do your daily activities affectEarth’s available resources?

SummaryPopulation and Carrying Capacity

• Population growth rate has rapidly increasedsince 1800.

• The human population might reach Earth’scarrying capacity if resources are not usedwisely.

People and the Environment

• A person’s daily activities use resources andproduce waste.

• Less packaging produces less waste.

• Conserving resources can lessen our impacton land.

5. Research Information Some areas of the world areexperiencing a decrease in population. Find out whereand some reasons for the decrease.

Packaging Produces WasteThe land is changed when resourcesare removed from it. The environ-ment is further impacted whenthose resources are shaped intousable products. After the productsare produced and consumed, theymust be discarded. Look at Figure 4.Unnecessary packaging is only oneof the problems associated withwaste disposal.

The Future As the populationcontinues to grow, more resourcesare used and more waste is created.If these resources are not usedwisely and if waste is not managedproperly, environmental problemsare possible. What can be done toprevent these problems? As you learn more about howyou affect the environment, you’ll discover what you cando to help make the future world one that everyone canlive in and enjoy. An important step that you can take isto think carefully about your use of natural resources. Ifyou conserve resources, you can lessen the impact on theenvironment.

Figure 4 Packagingfoods for single servingsuses more paper andplastic than buying foodin bulk does.

earth.msscience.com/self_check_quizAaron Haupt

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578 CHAPTER 20 Our Impact on Land

Land UsageYou may not think of land as a natural resource. Yet it is as

important to people as oil, clean air, and clean water. We useland for agriculture, logging, garbage disposal, and urban devel-opment. These activities often impact Earth’s land resources.

Agriculture About 16 million km2 of Earth’s total land sur-face is used as farmland. To feed the growing world population,some farmers use higher-yielding seeds and chemical fertilizers.These methods help increase the amount of food grown on eachkm2 of land. Herbicides and pesticides also are used to reduceweeds, insects, and other pests that can damage crops.

Organic farming techniques, as shown in Figure 5, use nat-ural fertilizers, crop rotation, and biological pest controls. Thesemethods help crops grow without using chemicals. However,organic farming cannot currently produce enough food to feedall of Earth’s people.

Whenever vegetation is removed from an area, such as a construction site or tilled farmland, soil is exposed. With-out plant roots to hold soil in place, nothing prevents the soil from being carried away by running water and wind.Several centimeters of topsoil may be lost in one year. In someplaces, it can take more than 1,000 years for new topsoil to develop.

■ Identify ways that land is used.■ Explain how land use creates

environmental problems. ■ Identify things you can do to

help protect the environment.

Using land responsibly will helpconserve this natural resource.

Review Vocabularyerosion: a process that wearsaway surface materials andmoves them from one place toanother

New Vocabulary

• stream discharge

• sanitary landfill

• hazardous waste

• enzyme

Using Land

Figure 5 Organic farms such asthis one reduce the environmentalimpact of chemicals on land. Compare and contrast organicfarming and other techniques.

Paul Bousquet

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SECTION 2 Using Land 579

Reducing Erosion Some farmers practice no-till farm-ing, as shown in Figure 6. They don’t plow the soil from harvestuntil planting. Instead, farmers plant seed between the stubbleleft from the previous year.

Other methods also are used to reduce soil loss. One methodis contour plowing. The rows are tilled across hills and valleys.When it rains, water and soil are captured by the plowed rows,reducing erosion. Other techniques include planting trees inrows along fields. The trees slow the wind, which reduces theamount of soil blown from the land. Cover crops, crops that arenot harvested, also can be planted to reduce erosion.

Feeding Livestock Land also is used for feeding livestock.Animals such as cattle eat vegetation and then are used as foodfor humans. About sixty-five percent of the farmland in Texas isused for grazing cattle. Other regions of the United States suchas the west and midwest also set aside land as pasture. Otherland is used to grow crops to be fed to cattle. Many farmers raisecorn and hay for this purpose. These crops provide cattle with avariety of nutrients and can improve the quality of the meat.

Figure 6 No-till farming canreduce erosion of topsoil. Describe other techniques that canbe used to reduce soil erosion.

Modeling Earth’sFarmlandProcedure

1. Cut an apple into fourquarters and set asidethree. One quarter ofEarth’s surface is land. Theremaining 3/4 is coveredwith water.

2. Slice the remaining quarterinto thirds.

3. Set aside two of the threepieces, because 2/3 ofEarth’s land is too hot, toocold, or too mountainousto farm or live on.

4. Carefully peel the remain-ing piece. This representsthe usable land surfacethat must support theentire human population.

AnalysisWhat may happen if availablefarmland is converted to otheruses?

Gene Alexander/Soil Conservation Service

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Forest Resources According to the Food andAgriculture Organization of the United Nations,approximately one-fourth of the land area on Earth iscovered by forest. About 55% of this forest is found indeveloping countries. The remaining 45% occurs indeveloped countries. The distribution of Earth’s for-est according to region is shown in Figure 7.

Deforestation is the clearing of forested land foragriculture, grazing, development, or logging. It isestimated that the amount of forested land in theworld decreased by 0.24% (94,000 km2) each yearbetween 1990 and 2000. Most of this deforestationoccurred in tropical regions.

What is deforestation?

Many people are concerned about forest conser-vation and management. For example, tropical rainforests contain diverse populations of plants and ani-mals that don’t live in other places. Many of theseplants might be important for developing new medi-cines. Some people also worry that removing toomuch of these forests could lead to the extinction ofsome organisms. Scientists currently are doingresearch to better understand the effects of deforesta-tion on species of plants and animals.

Cutting trees can have a regional effect on climateas well. Water from tree leaves evaporates into theatmosphere where it can condense to form rain. Ifmany trees are cut down, less water enters the atmo-sphere and the region receives less rainfall. This is oneway humans can affect the water cycle.

Forested Land by Region

North America13.2%

Europe27.0%

Asia/Oceania17.2%

Latin America and the Caribbean

27.5%

Africa15.1%Figure 7 Forests occur in

many regions on Earth. Use Graphs Which region hasthe most forested land?

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SECTION 2 Using Land 581

Development From 1900 to 2000, the number of kilometersof urban roadways in the United States increased by more than13 percent. Highway building often leads to more paving asoffice buildings, stores, and parking lots are constructed.

Paving land prevents water from soaking into the soil. Instead,it runs off into sewers or streams. A stream’s discharge increaseswhen more water enters its channel. Stream discharge is the vol-ume of water flowing past a point per unit of time. During heavyrainstorms in paved areas, rainwater flows directly into streams,increasing stream discharge and the risk of flooding.

Many communities use underground water supplies fordrinking. Covering land with roads, sidewalks, and parking lotsreduces the amount of rainwater that soaks into the ground torefill underground water supplies.

Some communities, businesses, and private groups pre-serve areas rather than pave them. Land is set aside for envi-ronmental protection, as shown in Figure 8. Preserving spacebeautifies the environment, increases the area into which watercan soak, and provides space for recreation and other outdooractivities.

Figure 8 Some land in urbanareas is preserved, such as this areanear Portland, Oregon.Discuss how preserving greenspace near cities helps protect theenvironment.

It’s not unusual for streams and riversto flood after heavy rain. The amount

of water flowing quickly into waterwaysmay be more than streams and riverscan carry. Land use can affect howmuch runoff enters a waterway. Wouldchanging the landscape increase flood-ing? Use your ability to interpret a datatable to find out.

Identifying the Problem The table above lists the percentageof rainfall that runs off land. Comparethe amount of runoff for each of theland uses listed. Assume that all ofthe regions are the same size and havethe same slope. Looking at the table,do you see a relationship between whatis on the land and how much waterruns off of it?

How does land use affect stream discharge?

Solving the Problem 1. Two years after construction of

a commercial development neara stream, houses downstreamflooded after a heavy rain. Whatcontributed to the flooding?

2. What are some ways that devel-opers can help reduce the riskof flooding?

Rich Iwasaki

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582 CHAPTER 20 Our Impact on Land

Sanitary Landfills Land also is used when consumed prod-ucts are thrown away. About 60 percent of our garbage goes intosanitary landfills. A sanitary landfill, like the one illustrated inFigure 9, is an area where each day’s garbage is deposited andcovered with soil. The soil prevents the deposit from blowingaway, helps decompose some materials, and reduces the odorproduced by the decaying waste.

Sanitary landfills also are designed to prevent liquid wastesfrom draining into the soil and groundwater below. New sani-tary landfills are lined with plastic, concrete, or clay-rich soilsthat trap the liquid waste. Because of these linings, sanitarylandfills greatly reduce the chance that pollutants will leak intothe surrounding soil and groundwater.

Since many materials do not decompose in landfills, or theydecompose slowly, landfills fill with garbage, and new ones mustbe built. Locating an acceptable area to build a landfill can bedifficult. Type of soil, the depth to groundwater, and neighbor-hood concerns must be considered.

Hazardous Wastes Some of the wastes that are thrown away are dangerous to

organisms. Wastes that are poisonous, that cause cancer, or thatcan catch fire are called hazardous wastes. Previously, every-one—industries and individuals alike—put hazardous wastesinto landfills, along with household garbage. In the 1980s, manystates passed environmental laws that prohibit industries fromdisposing of hazardous wastes in sanitary landfills. New tech-nologies which help recycle hazardous wastes have decreased theneed to dispose of them.

Figure 9 The majority ofgarbage is deposited in sanitarylandfills designed to containgarbage and prevent contamin-ation of the surrounding landand water.Describe the problems associatedwith landfill disposal.

Garbage Soil

Fluid collectionsystem

Cement, clay,or plastic liner

Gravel/Rock layer

Pipes for venting gas

Nuclear Waste Wastesfrom nuclear powerplants must be storedsafely because radioactiv-ity is dangerous. The U.S.government is currentlystudying a site in Nevadafor nuclear waste dis-posal because the area isremote, little rain falls,and the undergroundwater supply is far belowthe proposed storagefacility. What is radioac-tivity and how can itharm the environment?

Simon Fraser/Northumbrian Environmental Management Ltd./Science Photo Library/Photo Researchers

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Metal recovery

CuCuCuCu CuCu

CuCu

CuCu

CuCuCuCu

CuCu

Metal absorbed

Composting Burning

Ash disposal

SECTION 2 Using Land 583

Household Hazardous Waste Unlike most industries, indi-viduals discard hazardous wastes such as insect sprays, batteries,drain cleaners, bleaches, medicines, and paints in the trash. Itmay seem that when you throw something in the garbage, it’sgone and you don’t need to be concerned with it anymore.Unfortunately, some garbage can remain unchanged in a landfillfor hundreds of years. You can help by disposing of hazardouswastes at special hazardous waste-collection sites. Contact yourlocal government to find out about collections in your area.

Phytoremediation Hazardous substances can contaminatesoil. These contaminants may come from nearby industries orleaking landfills. Water contaminated from such a source can fil-ter into the ground and leave the toxic substances in the soil.Some plants can help fix this problem in a method called phyto-remediation (FI toh ruh mee dee AY shun). Phyto means “plant”and remediation means “to fix or remedy a problem.”

During phytoremediation, roots of certain plants such asalfalfa, grasses, and pine trees can absorb metals, including cop-per, lead, and zinc from contaminated soil just as they absorbother nutrients. Figure 10 shows how metals are absorbed fromthe soil and taken into plant tissue.

What happens to these plants after they absorb metals? Iflivestock were to eat contaminated alfalfa, the harmful metalscould end up in your milk or meat. Plants that become concen-trated with metals from soil eventually must be harvested andeither composted to recycle the metals or burned. If these plantsare destroyed by burning, the ash residue contains the haz-ardous waste that was in the plant tissue and must be disposedof at a hazardous waste site.

Breaking Down Organic PollutantsLiving things also can clean up pollutants

other than metals. Substances that contain carbon and other ele-ments like hydrogen, oxygen, and nitrogen, are called organiccompounds. Examples of organic pollutants are gasoline, oil,and solvents.

Organic pollutants can be broken down into simpler, harm-less substances, some of which plants use for growth. Someplant roots release enzymes (EN zimez) into the soil. Enzymesare substances that make chemical reactions go faster. Enzymesfrom plant roots increase the rate at which organic pollutantsare broken down into simpler substances. Plants use these sub-stances for growth.

How do enzymes affect organic pollutants in soil?

Figure 10 Metals such as cop-per can be removed from soil andbe absorbed by plant tissues.State why this vegetation can’t befed to livestock.

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584 CHAPTER 20 Our Impact on Land

Self Check1. List six ways that people use land.

2. Discuss environmental problems that can be created byagriculture and trash disposal.

3. Infer what you can do that would benefit the environment.

4. Describe how development can increase flooding.

5. Think Critically Preserving land beautifies the environ-ment, provides recreational space, and benefits futuregenerations. Are there any disadvantages to settingaside large areas of land as natural preserves?

SummaryLand Usage

• Pesticides and herbicides may be used onfarms to grow more food per km2.

• No-till farming can reduce erosion.

• Development can increase runoff.

• A sanitary landfill is designed to protect soiland groundwater.

Hazardous Wastes

• New technologies help recycle hazardouswastes.

• Hazardous wastes can be broken down byenzymes or phytoremediation.

Natural Preserves

• Many countries set aside land for protection.

6. Form a Hypothesis Develop a hypothesis about howmigrating birds might be affected by cutting down forests.

Natural Preserves Not all land on Earth is being utilized to produce usable

materials or for storing waste. As shown in Figure 11, some landremains mostly uninhabited by people. National forestlands,grasslands, and national parks in the United States are protectedfrom many problems that you’ve read about in this section. Inmany other countries throughout the world, land also is setaside for natural preserves. As the world population continuesto rise, the strain on the environment may worsen. Preservingsome land in its natural state will benefit future generations.

Figure 11 Many countries setaside land in the form of nationalparks as natural preserves.Discuss how natural preservesmight benefit humans and otherliving things.

Olympic N.P.

Mount Rainier N.P.

CraterLake N.P.Lassen Volcanic N.P.

Glacier N.P.

Yellowstone N.P.

Badlands N.P.

Rocky Mountain N.P.

Grand Canyon N.P.

Canyonlands N.P.

Saguaro N.P.Carlsbad Caverns N.P.

Big Bend N.P.

Yosemite N.P.

DeathValleyN.P.

Kings Canyon/Sequoia N.P.

Joshua Tree N.P.

Isle Royale N.P.

Mammoth Cave N.P.

Acadia N.P.

Great SmokyMountains N.P.

Shenandoah N.P.

Everglades N.P.

earth.msscience.com/self_check_quiz(tl)Gloria H. Chomica/Masterfile, (r)Raymond Gehman/CORBIS, (bl)David Muench/Getty Images

519-S2-MSS05ges 8/20/04 12:59 PM Page 584

What items in your house will end up in a land-fill? You might think about milk jugs or foodscraps. What about old clothing? In this lab,you’ll observe what happens to different typesof clothes that are buried in a landfill.

Real-World QuestionDo materials decompose at the same rate?

Goals■ Compare the decomposing rates of natural

and artificial clothing materials.■ Infer the effect of these materials on landfills.

Materials identical baking trays (2) garden soilclothing made of natural fibers (linen, cotton,

wool, silk)clothing made of artificial materials (fleece,

polyester, acrylic, rayon)toothpickstransparent tapescissorsspray bottle filled with water

Safety Precautions

Procedure1. Collect several articles of clothing and sepa-

rate those made with natural fibers fromthose made from artificial materials.

2. Cut 3-cm squares of each type of clothing.

3. Cut 1-cm � 3-cm labels from a sheet ofnotebook paper, and write one label foreach of your clothing squares. Tape eachlabel to the tip of a toothpick.

4. Fill each tray halfway with garden soil. Layyour artificial cloth squares in one tray andyour natural cloth squares in the other tray. Becertain the squares don’t overlap. Thoroughlymoisten all squares using the spray bottle.

5. Identify each clothing square by attaching atoothpick label.

6. Cover your squares withsoil. Moisten the soiland place the trays in adark place. Keep the soilmoist for three weeks.

7. After three weeks, dig upyour samples and observe each square. Recordyour observations in your Science Journal.

Conclude and Apply1. Compare the amount of decomposition of

the two types of materials.

2. Infer the effects of clothing made withnatural materials on landfills.

3. Infer the effects of clothing made withartificial materials on landfills.

4. Research materials used to manufactureclothing. Determine if the material is madefrom recycled products such as plastic bottles.

What to Wear?

LAB 585

Compare the types of clothing worn by yourclassmates with the types you used in yourexperiment. Contrast the results of theirexperiments with your observations. Formore help, refer to the Science SkillHandbook.

John Evans

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Figure 12 A person in theUnited States uses moreresources than the averageperson elsewhere.

586 CHAPTER 20 Our Impact on Land

Resource UseResources such as petroleum and metals are important for

making the products you use every day at home and in school.For example, petroleum is used to produce plastics and fuel.Minerals are used to make automobiles and bicycles. However,if these resources are not used carefully, the environment canbe damaged. Conservation is the careful use of earth materi-als to reduce damage to the environment. Conservation canprevent future shortages of some materials, such as certainmetals.

Reduce, Reuse, RecycleDeveloped countries such as the United States use more

natural resources than other regions, as shown in Figure 12.Ways to conserve resources include reducing the use of materi-als, and reusing and recycling materials. You can reduce theconsumption of materials in simple ways, such as using bothsides of notebook paper or carrying lunch to school in anondisposable container. Reusing an item means findinganother use for it instead of throwing it away. You can reuse oldclothes by giving them to someone else or by cutting them intorags. The rags can be used in place of paper towels for cleaningjobs around your home.

■ Identify three ways to conserveresources.

■ Explain the advantages ofrecycling.

Conserving resources helps reducesolid waste.

Review Vocabularyconsumption: using up materials

New Vocabulary

• conservation

• composting

• recycling

Conserving Resources

Yearly Consumption per Person

U.S. Rest of world

Oil(L)

Steel(kg)

Metals(kg)

Paper(kg)

3,800

700

340

151

31

5

328

181

519-S3-MSS05ges 8/20/04 1:01 PM Page 586

SECTION 3 Conserving Resources 587

Reusing Yard Waste Outdoors, you can do helpful things,too. If you cut grass or rake leaves, you can compost these itemsinstead of putting them into the trash. Composting means pilingyard wastes where they can decompose gradually. Decomposedmaterial provides needed nutrients for your garden or flowerbed. Some cities no longer pick up yard waste to take to landfills.In these places, composting is common. If everyone in theUnited States composted, it would reduce the trash put intolandfills by 20 percent.

Recycling Materials Using materials again is calledrecycling. When you recycle wastes such as glass, paper, plastic,steel, or tires, you help conserve Earth’s resources, energy, andlandfill space.

Paper makes up about 40 percent of the mass of trash. Asshown in Figure 13, Americans throw away a large amount ofpaper each year. Recycling this paper would use 58 percent lesswater and generate 74 percent less air pollution than producingnew paper from trees. The paper shown in the figure doesn’teven include newspapers. More than 500,000 trees are cut everyweek just to print newspapers.

Companies have found that recycling can be good for busi-ness. For example, companies can recover part of the cost ofmany materials by recycling the waste. Some businesses usescrap materials such as steel to make new products. These prac-tices save money, benefit the environment, and reduce theamount of waste sent to landfills.

Figure 14 shows that the amount of material deposited inlandfills has decreased since 1980. In addition to saving landfillspace, reducing, reusing and recycling can reduce energy useand minimize the need to extract raw materials from Earth.

Figure 13 People in theUnited States throw awayenough office and writing papereach year to build a wall 3.6 mhigh stretching from New YorkCity to Los Angeles.

Classifying Your Trashfor One DayProcedure1. Label a table with the

following columns: Paper,Plastic, Glass, Metal, andFood Waste.

2. Record items you throwout in one day. At the endof the day, count the num-ber of trash items in eachcolumn.

3. Rank each column bynumber from the fewesttrash items to the mosttrash items.

Analysis1. Compare your rankings

with those of others inyour household.

2. What activities can youchange to decrease theamount of trash youproduce?

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Figure 14

VISUALIZING TRASH DISPOSAL

588 CHAPTER 20 Our Impact on Land

lthough trash production in theUnited States is increasing, theamount of trash deposited in

landfills is decreasing. In 1980, 82 per-cent of discarded trash ended up in alandfill. Today, only 55 percent is takento the dump—thanks to the use ofwaste-reducing methods such as thoseshown below.

1980 1990 2000

Kg o

f tra

sh p

er p

erso

n pe

r yea

r

RECYCLING In 1980, about nine per-cent of trash was recycled. Now nearly 30 percent of America’s trash is reused.

COMPOSTINGYard trimmingsplaced in a pilewill decomposeand form a sub-stance called com-post. Compostthen can be usedon flowers andvegetables to helpthem grow.

400

500

600

700

800

900ALandfill Use in the United States

WASTE TO ENERGY Some waste material can be burned to produce electricity. This plantin Rochester, Massachusetts,burns trash to generate electric-ity for a local paper company.

▼

▼

▼Trash generated

Trash deposited in landfills

(graph photos)PhotoDisc; Digital Stock; Image Ideas, (tl)Philip James Corwin/CORBIS, (inset)Bill Gallery/Stock Boston/PictureQuest, (cr)Skiold/PhotoEdit/PictureQuest, (br)Aerials Only

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SECTION 3 Conserving Resources 589

Self Check1. List four advantages and two disadvantages of recycling.

2. Compare and contrast reducing and reusing materials.

3. List two simple ways that you and your classmates canreduce your consumption of Earth materials.

4. Think Critically Why is it more important to conserveresources as the human population increases?

SummaryResource Use

• Earth’s resources are used to make products.

• Conservation of resources can help preventfuture shortages.

Reduce, Reuse, Recycle

• There are many simple ways to reduce theamount of materials you use.

• Composting yard waste reduces trash in land-fills and provides nutrients for plants.

• Recycling materials can save money, benefitthe environment, and save landfill space.

5. Research Information Contact a sanitary landfill nearyou. Find out how long it will take for your commu-nity’s landfill to be full. How will waste be disposed of after the landfill is full?

Recycling Methods What types of recyclingprograms does your state have? Many states or citieshave some form of recycling laws. For example, insome places people who recycle pay lower trash-collection fees. In other places a refundable depositis made on all beverage containers. This means pay-ing extra money at the store for a drink, but you getyour money back if you return the container to thestore for recycling.

How have states and citiesencouraged people to recycle?

There are several disadvantages to recycling.More people and trucks are needed to haul materi-als separately from your trash. The materials thenmust be separated at special facilities like the oneshown in Figure 15. In addition, demand for thingsmade from recycled materials must exist, and itemsmade from recycled materials often cost more.

The Population Outlook The human popu-lation explosion already has had an effect on theenvironment and the organisms that inhabit Earth. It’s unlikelythat the population will begin to decline in the near future. Tomake up for this, resources must be used wisely. Conservingresources by reducing, reusing, and recycling is an importantway that you can make a difference.

Figure 15 In recycling facilitieslike this one, materials must beseparated before they can bereused.

earth.msscience.com/self_check_quizDavid Young-Wolff/PhotoEdit, Inc.

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Real-World QuestionEvery second, five people are born on Earth and two or three peopledie. As a result, there is a net increase of two or three people in theworld every second of every day. That amounts to about 81 millionnew people every year. This is nearly equal to the population ofCentral Africa. What effects will this rapid increase in human popula-tion have on Earth? How crowded will different regions of Earthbecome in the next ten years?

Procedure1. Copy the data table below in your Science Journal.

2. Lay the map out on a table. The map represents Earth and thepeople already living here.

3. Each minute of time will represent one year. During your firstminute, place 78 popcorn kernels on the continents of your map.Each kernel represents 1 million new people.

4. Place one kernel inside the borders of developed countries such asthe United States, Canada, Japan, Australia, and countries inEurope. Place 77 kernels inside the borders of developing nationslocated in South America, Africa,and Asia.

5. Continue adding 78 kernels toyour map in the same fashioneach minute for 10 min. Recordthe total population increase foreach year (each minute of the lab)in your data table.

Goals ■ Demonstrate the

world’s human popula-tion increase in thenext decade.

■ Predict the world’spopulation in 50 years.

■ Record, graph, andinterpret populationdata.

Materials small objects such as

popcorn kernels ordried beans (1,000)

large map of the world(the map must showthe countries of theworld)

clock or watchcalculator

Safety Precautions

Never eat or taste any-thing in the lab, even ifyou are confident that youknow what it is.

A WHrld Full of People

590 CHAPTER 20 Our Impact on Land

Population Data

Time Total Population (in years) Increase

1 78 million

2

3

4

5

6

7

8

9

10

Do not write inthis book.

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Analyze Your Data1. Draw and label a graph of your data showing the time in years

on the horizontal axis and the world population on the verticalaxis.

2. Calculate the world’s population in 50 years by using an averagerate of 71 million people per year.

3. Determine world population in ten years if only 4.5 million peo-ple are added each year.

Conclude and Apply1. Infer how many new people will be added to Earth in the next

10 years. Determine the world’s population in 10 years.

2. Compare the population growth in developed countries to thegrowth of developing countries.

3. Discuss ways the increase in the human population will affectEarth’s resources in the future.

Draw your graph on a computer andpresent your findings to the class. For morehelp, refer to the Science Skill Handbook.

LAB 591(t)SuperStock, (b)Matt Meadows

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SCIENCEANDSocietySCIENCE ISSUES

THAT AFFECTYOU!

Hazardous Waste

Research Find out more about incineration. Then use thisfeature and your research to conduct a class debate about theadvantages and disadvantages of incineration. For more information, visit

earth.msscience.com/time

During much of the 1980s, this signgreeted visitors to Love Canal, a housingproject in Niagara Falls, New York. The

housing project was closed because it had beenbuilt on a hazardous waste dump and peoplewere getting sick. Exposure to hazardous wastecan cause nerve damage, birth defects, and low-ered resistance to disease.

The Environmental Protection Agency (EPA)estimates that U.S. industries produce about265 million metric tons of hazardous wastes eachyear. Much of this waste is recycled or convertedto harmless substances. About 60 million tons ofhazardous waste, however, must be disposed of ina safe manner. Incineration, or burning, is oneway to dispose of hazardous wastes. However, thesafety of this method is hotly debated.

For IncinerationPeople in favor of incineration note that, if

done correctly, it destroys 99.99 percent of toxicmaterials. Although the remaining ash must still

be disposed of, it is often less hazardous than theoriginal waste material. Supporters also note thatincineration is safer than storing the hazardouswastes or dumping them in landfills.

Against IncinerationOther people say that incinerators fail to

destroy all hazardous wastes and that some toxinsare released in the process. They also note that newsubstances are generated during incineration, andthat scientists don’t yet know how these new sub-stances will impact the environment or humanhealth. Lastly, they say that incineration mayreduce efforts to reuse or recycle hazardous wastes.

While the debate goes on, scientists continueto develop better methods for dealing with haz-ardous wastes. As Roberta Crowell Barbalace, anenvironmental scientist, wrote in an article, “In anideal environment there would be no hazardouswaste facilities. The problem is that we don’t live inan ideal environment ... Until some new technol-ogy is found for dealing with or eliminating haz-ardous waste, disposal facilities will be necessary toprotect both humans and the environment.”

It causeshealth

risks, buthow do wesafely getrid of it?

Danger: Hazardous Waste Area.Unauthorized Persons Keep Out.

A danger sign ina garbage dumpalerts visitors tothe presence ofhazardous waste.

VCG/FPG

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Copy and complete the concept map about using land.

Population Impact onthe Environment

1. Modern medicine, clean water, and betternutrition have contributed to the humanpopulation explosion on Earth.

2. Earth’s resources are limited.

3. Our daily activities use resources and pro-duce waste.

Using Land

1. Land is used for farming, grazing livestock,lumber, development, and disposal.

2. Farming and development are ways thatusing land can impact the environment.

3. Using forest resources can impact organ-isms and Earth’s climate.

4. Plants are sometimes used to breakdown and absorb pollutants from contami-nated land.

5. New technologies have reduced greatly theneed for hazardous waste disposal.

6. One way to preserve our land is to set asidenatural areas.

Conserving Resources

1. Recycling, reducing, and reusing materialsare important ways to conserve naturalresources.

2. Reducing, reusing, and recycling hasdecreased the amount of trash deposited inlandfills since 1980.

3. Different methods can be used to encour-age recycling.

CHAPTER STUDY GUIDE 593

include include include

Forest resources

Resources anddevelopment

Using Land

Agriculture Disposal

Forest lands

Feeding livestock Hazardous waste

Parks

ways

include

earth.msscience.com/interactive_tutor(l)Stacy Pick/Stock Boston, (r)Tom Bean/Stone/Getty Images

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594 CHAPTER REVIEW

Fill in the blanks with the correct words.

1. The total number of individuals of a partic-ular species in an area is called .

2. means using resources carefullyto reduce damage to the environment.

3. means using materials again.

4. The maximum number of individuals of aparticular species that the environment cansupport is called .

5. The volume of river water flowing past apoint per unit of time is called .

Choose the word or phrase that best answers thequestion.

6. Where is most of the trash in the UnitedStates disposed of?A) recycling centersB) landfillsC) hazardous waste sitesD) compost piles

7. Between 1960 and 2000, world populationincreased by how many billions of people?A) 5.9 C) 1.0B) 4.2 D) 3.1

8. Which of the following is a substance thatcontaminates the environment?A) compost C) pollutantB) development D) groundwater

9. Which of the following might be poison-ous, cause cancer, or catch fire?A) enzymeB) compostC) metalsD) hazardous waste

10. What do we call an object that can beprocessed so that it can be used again?A) trash C) disposableB) recyclable D) hazardous

11. What is about 40 percent of the mass ofour trash made up of?A) glass C) yard wasteB) aluminum D) paper

12. What term is used to describe using plantsto clean up contaminated soil?A) recyclingB) compostingC) phytoremediationD) sanitary landfill

Use the illustration below to answer question 13.

13. How much more oil does each person usein the U.S. compared to the average useper person elsewhere?A) 310 L C) 189 LB) 3,100 L D) 27 L

Yearly Consumption per Person

U.S. Rest of world

Oil(L)

Steel(kg)

Metals(kg)

Paper(kg)

3,800

700

340

151

31

5

328

181

carrying capacity p. 575composting p. 587conservation p. 586enzyme p. 583hazardous waste p. 582

pollutant p. 576population p. 574recycling p. 587sanitary landfill p. 582stream discharge p. 581

earth.msscience.com/vocabulary_puzzlemaker

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CHAPTER REVIEW 595

14. Explain how reducing materials used forpackaging products would affect our dis-posal of solid wastes.

15. Discuss ways that land can be developedwithout changing stream discharge.

16. Infer Although land is farmable in severaldeveloping countries, hunger is a majorproblem in many of these places. Givesome reasons why this might be so.

17. Form a Hypothesis Forests in Germany aredying due to acid rain. What effects mightthis loss of trees have on the environment?

18. Describe how you could encourage yourneighbors to recycle their aluminum cans.

19. Classify Group the following materials ashazardous or nonhazardous: gasoline,newspaper, leaves, lead, can of paint, glass.

20. Concept Map Copy and complete this con-cept map about phytoremediation.

21. Compare and contrast farming and developingland. How do these activities affect streamdischarge?

22. Research Find out whether your commu-nity excludes yard waste from landfills.

23. Evaluate a Hypothesis Design an experimentto determine factors that decrease the timeit takes for newspapers or yard wastes todecompose.

24. Display Make a display showing howpaving land can increase stream discharge.

25. Junk Mail Collect your family’s junk mail forone week and weigh it. Divide this weight bythe number of people in your home. Multiplythis number by 300 million (the U.S. popula-tion). If 17 trees are cut to make each metricton of paper, calculate how many trees arecut each year to make junk mail for the entireU.S. population.

26. Interpret ScientificIllustrations Onehectare, shownhere, is a squareof land measuring100 meters by100 meters. Howmany hectares are in50,000 m2 of land?

Use the table below to answer question 27.

27. Growth Rate Calculate the percent increase inworld population from 1960 to 1980 and from1980 to 2000. Infer what is happening to therate of population growth on Earth.

100 m

100

m 1 hectareor

10,000 m2

World Population

ationns)

0

4

1

earth.msscience.com/chapter_review

Contaminants in Soil

absorbed by

treatment treatment

goes to goes to

Recycle

Burning

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Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

Use the photo below to answer question 1.

1. Why do some farmers use no-till farming?A. to improve crop yieldsB. to reduce soil erosionC. to save fuelD. to reduce the use of fertilizer

2. Which term means decreasing the amountof material used?A. recycle C. reduceB. compost D. reuse

3. Which term describes using land to growcrops and raise farm animals?A. agriculture C. developmentB. landfill D. remediation

4. Which of the following is a substance thatmakes chemical reactions go faster?A. enzymeB. compostC. pollutantD. hazardous waste

5. Which term describes all the individuals ofone species that occupy an area?A. population explosionB. carrying capacityC. populationD. population limit

6. Which of the following describes how thehuman population on Earth changed dur-ing the last 50 years?A. It decreased.B. It increased.C. It didn’t change.D. It first increased, then decreased.

Use the circle graph below to answer questions 7 and 8.

7. Which material made up the largest por-tion of the municipal solid waste producedin the year 2000?A. plastics C. metalsB. paper D. wood

8. What percentage of waste was food scraps?A. 11.2 C. 5.5B. 6.7 D. 37.4

596 STANDARDIZED TEST PRACTICE

Others3.2%

Municipal Waste, 2000

Food scraps11.2%

Wood5.5%

Rubber,leather, and

textiles6.7%

Plastics10.7%

Metals7.8% Glass

5.5%

Paper37.4%

Yardtrimmings

12%

Keep Moving If you don’t know the answer to a multiplechoice question, mark your best guess and move on.

Gene Alexander/Soil Conservation Service

519-CR-MSS05ges 8/20/04 12:58 PM Page 596

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

9. List three ways that people affect theenvironment.

10. How does unnecessary packaging increasethe amount of solid waste? How can thiswaste be reduced?

11. Why are many people concerned aboutthe loss of tropical forest?

12. What are hazardous wastes? How are theydifferent from other types of waste?

13. Should household hazardous waste beincluded with the normal trash? Explain.

14. What is phytoremediation? Why can’tplants used in phytoremediation be usedto feed livestock?

Use the graph below to answer questions 15–17.

15. What percentage of municipal wastes wererecycled in 2000?

16. How much higher is the percentage ofwaste recycled in 2000 than in 1960?

17. Describe the trend shown on the graph.

Record yours answers on a sheet of paper.

Use the diagram below to answer questions 18–21.

18. Why are the gas venting pipes shown onthe diagram necessary?

19. Why is a liner placed at the bottom of thelandfill?

20. What is a fluid collection system?

21. Explain why it is important to designlandfills this way.

22. Why have natural preserves been establishedin the United States and in other countries?

23. What is organic farming? How is it differ-ent from conventional farming?

24. Why have some communities preservedunpaved areas where rainwater can soakinto the ground?

25. Are there any disadvantages to recycling?Explain.

26. Why is human population growth cur-rently called a population explosion?

27. Why has human population increased sodramatically in the past century?

STANDARDIZED TEST PRACTICE 597

Municipal Solid Waste Recycled

20.0%

30.0%

10.0%

0.0%

40.0%

50.0%

Year

Perc

ent

of m

un

icip

al s

olid

was

tere

cycl

ed

1960

Source: U.S. Environmental Protection Agency

1970 1980 1990 2000

8.09.6

16.2

30.1

5.6

GarbageSoil

Fluid-collectionsystemCement, clay,

or plastic linerGravel/Rock layer

Pipes for venting gas

earth.msscience.com/standardized_test

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