Critical Thinking/Problem Solving - Earth Science
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Earth Science
Transcript of Critical Thinking/Problem Solving - Earth Science
Earth Science
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To the TeacherCritical Thinking/Problem Solving worksheets in this booklet exercise the students’ abilities to applythinking skills to situations related to concepts presented in the student edition. Students will applytheir knowledge to a new situation, analyze the new information, and synthesize in order to respondin a creative way. A series of responses that students might give are provided for you at the end ofthis booklet.
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Table of Contents
To the Teacher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Skills Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Activities 1 Earth’s Last Frontier—Hydrothermal Vents . . . . . . . . . . . . . 1
2 Atomic Energy—Good and Bad . . . . . . . . . . . . . . . . . . . . . . . 2
3 Phosphates—Help or Hazard? . . . . . . . . . . . . . . . . . . . . . . . . 3
4 Rock Solid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5 Sky-High Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6 Saving the Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7 Buffering Against Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8 Life on Mars? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9 Detecting Earthquake Patterns . . . . . . . . . . . . . . . . . . . . . . . . 9
10 Energy from Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11 Xenotime Dating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
12 Birds and Dinosaurs—Related or Not? . . . . . . . . . . . . . . . . . 12
13 Keeping the Atmosphere Healthy . . . . . . . . . . . . . . . . . . . . . . 13
14 Snowball Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
15 The Ocean—An Abundant Source of Salt . . . . . . . . . . . . . . . 15
16 The Mysterious Eel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
17 Plant-Based Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
18 Efforts to Neutralize Acid Precipitation . . . . . . . . . . . . . . . . . 18
19 The Pros and Cons of Gene Modification . . . . . . . . . . . . . . . 19
20 Controlling the Zebra Mussel . . . . . . . . . . . . . . . . . . . . . . . . . 20
21 Recycling in Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
22 Fighting Off the Winter Blues . . . . . . . . . . . . . . . . . . . . . . . . . 22
23 Early Skywatchers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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Critical ThinkingProblem Solving
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1ActivityEarth’s Last Frontier—
Hydrothermal VentsProblemSolving
In 1977, scientists found something so unusualand so hard to get to, it’s a wonder they ever madethe discovery. Three scientists, diving in a smallresearch submarine 2,348 m deep in the PacificOcean, discovered the first hydrothermal vent.
Hydrothermal vents are geysers in the oceanfloor. They are created when ocean water seepsinto Earth’s crust through cracks on the seafloor.The ocean water, heated by magma and hot rocks,spews out, carrying minerals from inside Earth.
Forming ChimneysWhen the hot water (380ºC or more) mixes withthe cold seawater (2ºC), it cools quickly. The min-erals in the water settle and gradually form depositsthat create a chimney at the opening of the vent.Because the chimneys spew hot, mineral-richwater, they can look like they’re smoking. Thediameter of the openings on the vents can be assmall as a few centimeters or as large as severalmeters. Scientists discovered one vent that was astall as a 16-story building and at least 183 m across.
Hydrothermal vents are found in all the oceans,but most are along an area of active volcanoesknown as the Mid-Ocean Ridge. They form whereocean plates have separated, allowing lava to flowthrough. To find a vent, scientists look for increasedseawater temperatures or volcanic activity.
Ocean Floor BiocommunitiesUntil hydrothermal vents were discovered, mostscientists thought organisms could not surviveat such great depths because of extreme pres-sure, absence of sunlight, and low tempera-tures. Scientists were surprised to find thatmany hydrothermal vents had thriving bio-communities around them. Giant tube wormsand blind shrimp are just some of the morethan 300 species found near the vents.
What is at the base of the food chain thatsupports these deep-sea animals? After analyz-ing the water, scientists discovered it is a type ofbacteria. This special bacteria can convert thetoxic sulfur from the vents into energy. Thisprocess of using chemicals rather than sunlightfor energy is called chemosynthesis. In turn,other vent organisms eat these bacteria or theyeat other organisms that eat the bacteria.
A New FrontierThe extreme depths make it difficult to locateand study hydrothermal vents, and the specialequipment required is expensive. Scientists haveexplored less than one percent of the seafloorwhere they think vents might be located.
Scientists do know that geothermal vents play animportant role in heating the world’s oceans andmaintaining their chemical balance. They also serveas an outlet for the heat within Earth’s crust. In thefuture, these unique ecosystems might prove to besources for new medicines and might even be minedfor their copper, gold, and manganese they emit.
Applying Problem Solving Skills1. If you had been able to interview one of the scientists who discovered the first hydrothermal
vents, what questions would you have asked? List at least three.
2. Why was the discovery of the sulfur-eating bacteria important to scientists’ understanding of thisunique ocean-floor ecosystem?
3. Why do you think hydrothermal vents are called “Earth’s last frontier”?
Ocean water is heated by magma below Earth’s surface.
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Atomic Energy—Good and Bad
The majority of chemical elements never change.An element might combine with other elementsto form compounds, but the structure of theatoms in each element remains the same. Suchelements are stable. Some elements, in contrast,are not stable. They change over time, becomingdifferent elements. As these elements change,they release energy. The energy they release iscalled radiation, so the elements are radioactive.
Once scientists understood the nature ofradioactive elements, they realized that all atomsstore a great deal of energy. Scientists found thatsplitting atoms releases energy in the form ofheat and radiation. Splitting atoms is known asfission. Fission happens when the atoms ofradioactive elements are bombarded with neu-trons. The neutrons penetrate the nucleus of theatom and cause the atoms to divide in half. Thissplitting causes the release of tremendousamounts of energy, which can be harnessed.
Uses of Nuclear EnergyThe first use of atomic energy was in warfare.Atomic bombs were made that split atoms uponimpact, producing waves of searing heat anddeadly levels of radiation. When the UnitedStates dropped fission bombs on Japan duringWorld War II, hundreds of thousands of peoplewere killed and much land was destroyed. Later,scientists learned to harness atomic energy forpeaceful means, such as generating electricity.
After the war, nuclear reactors were builtthroughout the world. In a nuclear reactor, atomsof radioactive elements are split. Some of the
energy released is in the form of heat. The heat isused to produce steam, which powers turbinesthat create electricity and provide power to citiesand factories.
In a nuclear reactor, the heat must be con-trolled. If too much heat builds up, it causes an explosion that releases radioactive elementsinto the air. The radioactive elements do notdisappear. They are absorbed by other elementsand can increase. Too much radiation is harm-ful to people, animals, and plants. It can causesickness and even death.
Chornobyl and BeyondBecause radiation is so harmful to living things,great care has been taken to create safety proce-dures to prevent accidents. But in 1986, an acci-dent did happen. In Chornobyl, Ukraine, part ofthe former Soviet Union, a steam buildup resultedin an explosion that released large amounts ofradiation into the atmosphere. The explosion dev-astated the area around the reactor and caused 31deaths. The radiation, blown by wind, wasdetected in places far away from Chornobyl.
Years later, the physical and psychologicaleffects of the accident are still evident. There isa significant increase in thyroid cancer, espe-cially among children. Anxiety and stress areapparent in people living in the affected areas.Large areas of agricultural land are stillexcluded from use due to contamination.Despite its risks, atomic power is very efficientand continues to be used in many placesthroughout the world.
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CriticalThinking
Applying Critical Thinking Skills1. Why is the use of nuclear energy controversial?
2. Do you think the benefits of nuclear power outweigh the potential dangers?
3. During the Cold War in the 1900s, the United States and the Soviet Union built up stores ofatomic weapons. At the end of the Cold War, they reached agreements to limit the number ofatomic weapons. Do you think all countries should agree to limit atomic weapons? Explain.
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3ActivityPhosphates—Help or Hazard?Problem
Solving
Phosphorus is part of who you are—from yourcells to your teeth and bones to your geneticblueprint material, DNA. Phosphorus, in theform of phosphates, is used by every livingorganism’s cells in the transfer of energy.
Phosphates in DetergentsPhosphates were used in the mid- to late-twentiethcentury, as laundry detergent additives to boostthe dirt-removing agents in the soap and to softenhard water. But phosphates soon made their wayinto lakes and streams, causing algae to feed on the phosphate compounds and grow out of con-trol. This growth, known as an algal bloom, killsfish and other aquatic life by using up all the available oxygen.
Phosphate detergents accounted for 30 to 70percent of Canada’s phosphate pollution in theyears before 1970. By the mid-1980s, manylocal governments in the United States hadbanned the use of phosphates in detergents.
The Mining ProcessThe United States, however, still faces phos-phate pollution problems—this time from themining and manufacturing of phosphate fertil-izers. China, Morocco, Russia, and the UnitedStates are world suppliers of phosphates usedfor fertilizers and other commercial needs.Florida produces 30 percent of the world’s sup-ply of phosphate fertilizers and 75 percent ofthis nation’s supply.
Phosphates are found naturally in phosphaterock. Manufacturers mine phosphate and pre-pare it for refining. The rock is crushed to makedry fertilizers or treated with sulfuric acid, achemical agent. Nearly 90 percent of phosphate
is mined for fertilizer and to make supplementsfor animal feed. The remaining 10 percent isused in making industrial chemicals.
Good News and Bad NewsPhosophate mining and fertilizer production arenot friendly to the environment. When phos-phates are treated at fertilizer manufacturingplants, fluorine gas is released. During the late1960s, fluorine emissions killed fish and causedcrippling diseases in livestock. Crops were dam-aged and, in some areas of Florida, citrus treesup to 80 km away from the processing plantswere destroyed.
Pollution regulations at state and federal levelshelped Florida turn its toxic wastes into revenue,however. By capturing fluorine gases and con-centrating them into a solution called fluorosili-cic acid, fertilizer manufacturers created whatthey call “fresh pollution concentrate.” The freshpollution concentrate is sold to cities across thecountry that use it to fluoridate water supplies.
Fluoridated water helps prevent cavities. It isthe most inexpensive way to deliver the benefitsof fluoride. The only other way is with directcontact to your teeth either in a dentist’s officeor by using one of the many toothpastes or flu-oride rinses available.
The fresh pollution concentrate was first sold more than three decades ago. Since thattime, however, no clinical studies have beenconducted on its use, and no federal safetystandards are in place. Only now are healthofficials being pressured by public interestgroups to investigate the safety of fluoridateddrinking water.
Applying Problem Solving Skills1. What do you expect will happen to Florida’s supply of phosphate rock over the next several
decades? What impact will that have on the United States?
2. Do you think a federal ban on phosphates in detergents should have been enacted? Why or why not?
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Rock Solid
Just as your ancestors used sticks, mud, and rocksto build their homes, people use stone to buildstructures today. Many buildings, streets, bridges,piers, and highways are made of stone.
Ninety-nine percent of all building stone isused in crushed form. Only one percent is cutinto slabs or blocks, called dimension stone.The best dimension stones have few pores oropenings in their surfaces. This helps themresist weathering because water can’t collect,freeze, and damage the stones easily. Some ofthe best dimension stones are made of lime-stone, marble, granite, sandstone, and slate.Structures built with these stones often lasthundreds of years.
LimestoneLimestone is an excellent building stone. Eventhough it is hard, it can be cut in any directionwithout splitting. It is used in the foundations,walls, sills, steps, and floors of buildings. Lime-stone in its crushed form is used for buildingroads, making cement and plaster, smeltingiron ore, making paper and glass, purifyingwater, and treating soil.
Marble and GraniteMarble is an elegant building stone. It is strongas well as fire-resistant and weather-resistant.Marble is usually white, but depending on theimpurities mixed with its calcite, it can be red,yellow, or green. Pure calcite marble is translu-cent; that is, light partially penetrates the stoneand is reflected back by inside surfaces. Marbleis used in buildings, monuments, and decora-tions. Crushed marble is used in road paving,roofing, stucco, and soaps.
Granite also has been used for building sinceancient times. It is strong and highly resistant to
weathering, but it is hard to cut. It often is usedin public buildings and monuments because itssurface can be polished to a shine. Crushedgranite is used in making concrete and rock-filled dams.
Sandstone and SlateSandstone comes in many colors, from cream tored, brown, and green. A reddish-brown sand-stone used for constructing houses in the easternUnited States is called brownstone. Well-cemented with silica, sandstone is resistant toweathering. Because early builders found thatsandstone was easy to cut with hand tools, it wasa common building stone. Crushed sandstone isused in concrete. It’s also used in making pot-tery, porcelain, glass, and abrasives.
Slate is a fine-grained rock that can be splitinto smooth, thin sheets. This makes it ideal forflooring and roofing. It’s both long-lasting andweatherproof. Chalkboards once were made ofslate. Today, crushed slate is used in road sur-facing and linoleum.
4Activity
CriticalThinking
Applying Critical Thinking Skills1. What kind of rock—igneous, metamorphic, or sedimentary—is each of the five stones described
above? Classify each and explain how its ability to be cut is related to its classification.
2. If you were carving a statue and you wanted it to be white, which stone would you use? Why? Ifyou were building a monument and you wanted to polish it, which stone would you use? Why?
Constitution Hall in Washington, D.C., was built of limestone in 1929.
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5ActivitySky-High ViewsProblem
Solving
For many years, when botanists went into thefield to study plant distribution, they wouldconsult a topographic map. With the integra-tion of computers into the everyday work ofscientists, fieldwork no longer requires papermaps. Instead, researchers are using the globalpositioning system (GPS) in conjunction withthe geographic information system (GIS). TheGIS lets scientists convert data into maps.
To use GPS, scientists need a receiver about thesize of a cell phone that picks up a signal sent by asystem of 24 satellites. This allows scientists todetermine their location to within 10 m. The loca-tion is displayed on a screen for immediate view-ing and can be downloaded later to computersequipped with GIS maps. Recently, the GPS/GISsystem has been modified to include video takenon the ground or from the air. This allows scien-tists to record videotaped data along with theexact location in which the video was shot.
A Variety of UsesPositioning technology is having a great impacton research methods. In Colorado, botanists areusing GPS and video cameras attached to air-planes to survey aspen groves and record theexact location of each grove.
Farmers can attach portable GPS receivers totheir tractors. The GPS unit can determine the
tractor’s exact location. Other sensors canrecord important factors, such as soil nutrientlevel or water content. This information can be relayed to an on-site personal computer.Farmers can use these data to make decisionsabout using fertilizer or irrigation. This newtechnology is called precision agriculture.
Some environmental health departments areusing the system to create maps of potentialsources of pollution. When there is a report ofcontamination, these maps help officialsquickly identify the source of the pollution andprevent further contamination.
Advantages over Traditional MapsWhile it does not replace traditional maps,the GPS/GIS system has several advantages.First, satellites can pinpoint locations withmore accuracy. Second, with airplane-recordedvideo, a much larger area can be observed in a short period of time. GPS receivers record data in great detail, allowing scientiststo zoom in on a small area without distortingdetails. Finally, video recording allows scien-tists to provide much more detailed data than simple field notes do. As more scientistsbecome familiar with the technology, thesemethods of fieldwork will have even moreapplications.
Applying Problem Solving Skills1. When using traditional maps, the mapped area decreases as the detail increases. This might force
a scientist in the field to carry numerous maps. How can a GPS receiver help a field scientist over-come this problem?
2. When fighting wildfires, often the commander directs many different groups of firefighters at dif-ferent remote locations. How might GPS/GIS aid the commander?
3. What might be some disadvantages of using aerial photography with GPS rather than on-the-ground observation when monitoring fern growth in a forest ecosystem?
4. Propose another application of GPS/GIS technology.
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Saving the Soil
Soil is a vibrant, changeable substance made upof many important nutrients. These nutrients,such as phosphorus, carbon, and nitrogen,make it possible for crops and other plants togrow and thrive. Many factors, including thetypes of plants grown and the way farmersgrow them, can change the composition ofsoil—for better or worse.
Problem PracticesSome popular methods of farming can rob soilof valuable nutrients or deposit harmful ele-ments. For example, irrigation of crops in manyplaces can cause excess salt deposits and pesti-cide residues to accumulate in soil, making itunsuitable for farming. Poorly managed irriga-tion also can lead to soil erosion. Experts todaybelieve that often it is better to work with a soil’snatural dry state, rather than to try to change itthrough irrigation.
Dryland FarmingDryland farming is a traditional agricultural
technique used in semiarid areas that don’t needirrigation. Irrigation can use up sources ofgroundwater in as few as 35 years. Drylandfarming uses only small amounts of fertilizercompared with irrigation farming.
In dryland farming, a crop-fallow rotation isused to conserve nutrients and water. Thismeans that a farmer will leave part, usually half,of the farmland unplanted for one growing sea-son. The unplanted ground is called fallow. Thefarmer then tills the stubble left by the previouscrop into the ground. As the nitrogen in thecrop stubble breaks down into nitrate, the fal-low ground gains nutrients. Adding smallamounts of fertilizer can further increase theamount of nitrate available in the soil.
Drawbacks and SolutionsDryland farming potentially raises nitrate levelsin groundwater. While land lies fallow, nitratefrom the crop stubble can be carried to ground-water by rain or melting snow. High levels ofnitrate in drinking water can cause serioushealth problems in humans.
Dryland farming can be improved throughconservation tillage. With this method, a farmerdoes not remove crop stubble from fallow land.Instead, the farmer leaves the crop stubble aloneand seeds the next crop on top of the stubble.Conservation tillage can increase crop yields,extend the growing season, and reduce runoff ofnitrates by rainfall by up to 60 percent.
6Activity
CriticalThinking
Applying Critical Thinking Skills1. Dryland farming can be an environmental problem when nitrates are released into groundwater.
How can dryland farming be an environmental advantage? Explain.
2. In what areas of the United States might experts recommend dryland farming?
Step 2—At planting
Step 1—At harvest
Dryland farming
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7ActivityBuffering Against ErosionProblem
Solving
In the 1930s, huge dust storms swept throughthe Great Plains in the southwestern UnitedStates. The thick clouds of dust were a result ofthe erosion of once-fertile farmland. The erosionwas caused by poor farming techniques and aneight-year drought in the area. Farmers who hadsettled in the region used techniques that werenot suited to this dry, treeless area. Overtillingand overgrazing, combined with the drought,eroded the fertile topsoil.
In response, in 1935, Congress declared soilerosion to be a national problem and created theSoil Conservation Service. The U.S. governmentpaid farmers to practice soil-conserving farmingtechniques. Today, around the world, erosionremains a key cause of desertification. Desertifica-tion is the process by which fertile land becomesarid or desert land. It is brought about by a cli-mate change or mismanagement of the land.
Erosion and PollutionErosion also can contribute to pollution. Erosioncaused by storm runoff can carry chemicals suchas fertilizers, pesticides, and herbicides into sur-face water. Scientists have found that naturalwetlands filter much of the possible contamina-tion resulting from agricultural runoff. Theyhave applied this knowledge to farming. Farmersplant areas next to waterways in their fields withnative plants rather than crops. The two maintypes, forest buffers and grass buffers, capturemuch of the sediment and chemicals that nor-mally drain off of farmland in rainwater.
Grass and forest buffers also help controlnitrate levels in the soil and groundwater. The
buffers’ roots encourage the growth of bacteriain the soil. These bacteria eat nitrates and otherchemicals deposited by fertilizers into thegroundwater. They convert the nitrates intoatmospheric nitrogen, reducing nitrate levels byup to 50 percent.
Reducing RunoffGrass waterways and grass hedges can be used toprevent erosion in areas with heavy rainfall. Bybuilding grass-covered pathways at the lowestlevel of a patch of farmland, farmers can divertrainfall to these pathways, away from their crops.Because the waterways are covered by grass, top-soil from them does not easily wash away. Grasshedges go further, trapping sediment from runoffas water flows through them. In addition, thehedges slow the pace of runoff, reducing its physi-cal effects on the land.
Forest buffers can be natural or managed. Amanaged forest buffer has three zones. The firstzone, extending at least 4.5 m from a stream,consists of native hardwood trees. The secondzone measures at least 6 m wide and containsconifers, hardwood trees, or shrubs. The thirdzone, a grass pathway, lies between the secondzone and the crop field. All three zones filter sed-iments and chemicals from runoff.
Buffers provide more benefits than just con-trolling farm runoff. Grass buffers also can beharvested as feed for livestock. They can be usedto control erosion on construction sites and inurban recreation areas. Zone two of forestbuffers can be harvested for timber or other forest products.
Applying Problem Solving Skills1. How are wetlands, grass buffers, and forest buffers alike? How do they differ?
2. Buffers alone cannot replace wise farming methods. Explain why.
3. Without any buffers in place, where do you think farm runoff would end up? What do you thinkthe effects of this runoff would be?
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Life on Mars?
With enough data, one day scientists might beable to finally answer the age-old question: Isthere really life on Mars? In hopes of learningmore about the possibility of life on Mars, sci-entists have been studying the geology of thered planet and have found some striking simi-larities to Earth.
Evidence of an Ancient OceanData about Mars have been collected since 1997by a spacecraft known as the Mars Global Sur-veyor. Using a laser, scientists collected altimetrydata, or measurements of the altitude of Mars’shorelines. Scientists now theorize that ancientMars was, indeed, home to an ocean that cov-ered one-quarter of its surface.
Three important pieces of information con-firm this belief: (1) the shoreline is level as itwould be if an ocean were present; (2) the areathat would have been the ocean floor issmoother than other parts of the planet; and(3) the volume of water needed to fill the spacethought to be the ocean is equal to the amountof water estimated to have existed on Mars.Scientists will continue to analyze new data sent by Surveyor to support or disprove theocean hypothesis.
A Cosmic Bar CodeIn addition, geologists have found evidence to suggest that Mars has something else incommon with Earth—plate tectonics. Using a
magnetometer, Surveyor collected thousands ofmagnetic readings that formed a pattern somehave called a “cosmic bar code.” The bar code isa series of magnetic stripes that run parallel toeach other. These stripes are remarkably similarto the magnetic stripes found on Earth. Fur-thermore, the magnetic poles on the stripesalternate from north to south, just like Earth’sdo. In fact, Earth’s magnetic stripes are a keyindicator of plate tectonics or geological shiftsin the ocean floor.
Tectonic forces cause something calledseafloor spreading. Seafloor spreading is createdwhen an ocean floor moves apart to makeroom for hot magma that bubbles up frombelow. Some scientists believe that the magneticstriping found on Mars, along with the evi-dence showing that Mars possibly had its ownocean, proves that seafloor spreading alsooccurred on Mars.
Scientists DisagreeEnough differences exist between Earth andMars that not all scientists agree about platetectonics on Mars. For one thing, the magneticstripes on Mars are much wider than the stripeson Earth. And, while magnetic patterns liealong all of Earth’s ocean floors, on Mars, scien-tists found magnetic striping only on thesouthern hemisphere. Also, the core of Mars,unlike Earth’s core, has cooled. That means tec-tonic forces no longer take place on Mars.
8Activity
ProblemSolving
Applying Problem Solving Skills1. Why is a smooth surface associated with the bottom of the ocean?
2. How does the presence of an ocean help answer the question about the possibility of life on Mars?
3. If plate tectonics is, or was, present on Mars, what other types of geological formations or occur-rences might you expect to find?
4. What other types of evidence, besides magnetic patterns, might you expect from a planet withplate tectonics?
5. As head of a research project, what would you do next to try to confirm the existence of life on Mars?
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9ActivityDetecting Earthquake PatternsCritical
Thinking
People have tried to predict earthquakes sincethe earliest times. The Roman general Pliny theElder theorized that earthquakes could be pre-dicted using these four warnings signs: (1)buildings that tremble slightly, (2) a low cloudspread over a wide area, (3) well water thatbecomes cloudy and stinks, and (4) animalsthat behave strangely.
Animal SenseAlthough Pliny’s theory was never proven,people have observed the strange behavior ofanimals before many earthquakes. In earlyGreece, one historian noted the mass exit ofmany animals from the city of Helice. Five daysafter the animals began leaving, the city wasdestroyed by an earthquake.
Animals might detect the tremors that pre-cede an earthquake, or they might behavestrangely because of escaping gases caused by tectonic activity. Perhaps animals behave differently because they sense a change in the weather.
Seismic SignsOf course, scientists don’t rely solely on animalbehavior to predict earthquakes. They study thehistory of areas to determine whether a cycle ofearthquakes exists. They measure the speed ofseismic waves and changes in the electricalresistance of rocks in major fault areas. Theyexamine the levels of radon and carbon dioxidein water. They identify areas in earthquake-prone regions that have not recently releasedseismic strain.
In 1975, seismologists successfully predictedthat an earthquake would strike Haicheng,
China. They did it by using scientific instru-ments and the observations of people who livedthere. People reported frequent tremors andtilting of the ground. Furthermore, theyreported that hibernating snakes awoke andfled their holes. Finally, about 12 h before theearthquake hit, the signs occurred so frequentlythat it seemed clear that an earthquake waslikely. Thousands of people were evacuatedfrom the area, and only a few people were killedwhen the earthquake struck.
Not all earthquakes, however, are precededby such clear signs. An earthquake struck thecity of Kobe, Japan, in 1995 without warning.In a quake that lasted only 20 s, nearly 6,400people lost their lives, 35,000 were injured, and400,000 were left homeless.
Applying Critical Thinking Skills1. Is it wise to rely on strange animal behavior as a sign for an upcoming earthquake? Explain.
2. At present, scientists can make fairly accurate, long-term predictions of earthquakes. Do youthink it’s possible for them to develop accurate, short-term predictions? Explain.
3. Millions of dollars are spent on prediction research. Should this money be used for other pur-poses? Why or why not?
This map shows the expected shaking intensity for Palo Alto, Cali-fornia, if an earthquake of 6.9 on the Richter Scale were to hit.
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Energy from Earth
Hydrothermal energy, a type of geothermalenergy, originates deep in the earth. It heatswater, which rises to Earth’s surface and escapesthrough gaps. These outlets are found in theground around volcanoes that are dormant ornearing extinction.
Hydrothermal FormationsA hot spring forms where there is a lot of high-temperature water and a wide opening to the sur-face. It bubbles continuously with hot water anddissolved minerals.
In places where there is little hot water and anarrow opening to the surface, a fumarole(FYEW muh rohl) forms. When water changesfrom a liquid to a vapor in an instant, it flashesinto steam and expands, taking up 1,600 timesmore space than the water. The steam moves upand drives the gases through the narrow opening.
A solfatara (sohl fuh TAHR uh) is a type of fumarole that emits steam and sulfurousgases. The areas around solfataras are rich with sulfur deposits.
Mud pots are bubbling pools of extremely hotmud. They form in spots where hot water com-bines with dissolved rock. They can form lowcones, called mud volcanoes.
Another kind of hydrothermal formation is a geyser. Scientists theorize that a geyser’sunderground channels are different from thoseof hot springs, fumaroles, and mud pots.Trapped in a complex system of tubes andpockets, water heats far beyond its normal boiling point. The superheated water expands,forcing some of the water toward the surface.This reduces the pressure on the superheatedwater below. The water then flashes to steam,
which shoots to the surface, carrying water with it. Geysers are rare. They occur in groups only in Iceland, New Zealand, Indonesia,and Yellowstone National Park in Wyoming and Idaho.
Tapping Earth’s PowerThe world’s largest energy resource, geothermalenergy, can generate electricity, warm green-houses, and heat and cool homes. Geothermalenergy is clean energy because its power plantsdo not emit nitrogen oxides and release onlylow levels of sulfur dioxide and carbon dioxide.If the energy can be captured, geothermalresources have the potential to provide nearlylimitless, pollution-free energy.
10Activity
CriticalThinking
Applying Critical Thinking Skills1. How does the amount of groundwater affect the formation of a hot spring, a fumarole, and
a mud pot?
2. What would be some advantages of a geothermal power plant compared with burning coal orusing nuclear power?
A fumarole ejects water vapor and other gases, such as carbondioxide and hydrogen sulfide.
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11ActivityXenotime DatingProblem
Solving
In an attempt to predict Earth’s future accurately,geologists need to understand the past. By lookingat various rocks and determining when andwhere they formed, scientists can learn aboutEarth’s formation and its changing structure.
Limited AccuracyThe most common method of dating rocks is bymeasuring the rate of radioactive decay of carbonin the rocks. Unfortunately, this method has notproven successful in dating rocks formed duringEarth’s first 4 billion years, the Precambrian time.Since Earth is only 4.6 billion years old, scientistsare left guessing about what happened duringmost of Earth’s existence.
Scientists have a relatively good understand-ing of the most recent 600 million years onEarth. This is due primarily to the rapidincrease in the number of living organismsduring that time and the fossils that they left.During the first 4 billion years on Earth, how-ever, what little life existed was small and leftfew fossils.
The fact that many Precambrian rocks are sed-imentary, formed largely from debris left by otherrocks, adds to this problem. In the past, scientistscould date such rocks only by measuring the ageof volcanic rocks around the sedimentary
rocks if, in fact, any existed. Using this method,scientists could say that the sedimentary rockformed between the dates when the volcanicrocks formed.
New Dating MethodA new technique, called xenotime dating, is help-ing scientists more accurately date rocks of thePrecambrian time. Xenotime dating gives scien-tists a more precise method for dating sedimen-tary rocks by determining when sediments in therocks were deposited.
Xenotime, a phosphate mineral found inmost sedimentary rocks, forms relatively shortlyafter sediments are deposited. Initially, xenotimecontains little lead but large amounts of ura-nium. As time passes, the uranium decays,forming more lead. By measuring the amountof lead existing in a sample of xenotime, scien-tists can determine the age of the rock contain-ing the sample.
This new process of radioactive dating willhelp scientists date sedimentary rock and givethem a better understanding of tectonicprocesses and plate positions. A better under-standing of how Earth’s crust has moved in thepast could prove valuable in predicting how itmight move in the future.
Applying Problem Solving Skills1. Scientists have shown that lead does not move from one crystal of xenotime into another. If it
did, how would that affect xenotime dating?
2. A geologist discovers a formation with two layers of sediment. The top layer shows a lead measure-ment of 27, and the bottom layer shows a measurement of 14. Analyze these data to determine therelative ages of the layers, and propose an explanation for the position of the sediments.
3. Earth’s existence can be separated into four time periods. From youngest to oldest, they are the Ceno-zoic era, the Mesozoic era, the Paleozoic era, and the Precambrian time. Sequence the time periods bythe amount of lead in the xenotime you would expect to find in sedimentary rocks from each timeperiod. Explain your sequence.
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Birds and Dinosaurs—Related or Not?
Can you learn about dinosaurs by watching birdsat a feeder? Scientists generally agree that dinosaurswere a type of reptile and that birds descendedfrom reptiles. Scientists don’t agree, however, onhow closely birds are related to dinosaurs.
Comparing TraitsTo see how closely related birds might be todinosaurs, scientists compare and contrast livingbirds with fossils of primitive species that mightbe related to birds. Using complex computer pro-grams, they look for matches in at least 80 physi-cal traits of modern birds. These traits include theskull, teeth, neck, pelvis, tail, shoulder, bones,hands, feet, ankles, and stance.
Scientists have found several species ofdinosaurs that had feathers. Several otherdinosaur species have bones similar to modernbirds—and unlike any other living animal.Some dinosaurs also had wrists that could bendin a flapping motion, like a wing, and toes thatwere arranged so they could grasp branches.
Mismatched TraitsOther traits make some scientists question therelationship between birds and dinosaurs. Afterstudying photographs of dinosaur fossils, some
scientists believe the abdominal cavity of sev-eral birdlike dinosaurs was more like those ofmodern-day crocodiles than birds. Crocodileshave a division in the chest cavity that allowsthe lungs to fill with air. When musclesattached to the liver and diaphragm contract,air is pulled into the lungs. Birds, in contrast,do not have this system. They have lungs thatallow air to flow through them without thehelp of a diaphragm.
Not a Simple QuestionBefore deciding if there’s a link between birdsand dinosaurs, scientists still must answer sev-eral questions. Were dinosaurs cold-blooded(like reptiles) or warm-blooded (like birds)?Some dinosaurs with feathers probably couldnot fly. If so, did the feathers develop to attractmates, or did they develop to insulate thedinosaurs? If the feathers could keep thedinosaurs warm, the dinosaurs must have beenwarm-blooded.
It’s likely that only one-fourth of alldinosaurs have been found in the fossil recordso far. That means that many links betweenbirds and dinosaurs or between birds andanother ancestor have yet to be found.
12Activity
ProblemSolving
Applying Problem Solving Skills1. How would you define bird, if a dinosaur with feathers is not a bird?
2. A species called Microraptor zhaoianus had feathers and toes that could have grasped treebranches, yet it probably could not fly. It had lightweight bones similar in structure to modern-day birds’ bones. It had a long tail like a dinosaur’s, and its teeth were arranged like those of adinosaur. Other dinosaur “birds” were much larger, however. Microraptor was about as big as acrow. Does any of this information help you answer the following questions: Are birds modern-day dinosaurs? Were dinosaurs cold- or warm-blooded? Did birds learn to fly from the ground upor from the trees down? Explain.
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13ActivityKeeping the
Atmosphere HealthyCriticalThinking
In the late 1800s and early 1900s, the first refrig-erators used toxic gases as coolants. These gasescaused fatal accidents when leaks occurred. In1928, chlorofluorocarbons (CFCs) were firstsynthesized as safer chemicals for refrigerators.CFCs are nontoxic, nonflammable, and stablegases. The stability of CFCs, however, poses athreat to the ozone layer.
CFCs’ Negative SideCFCs were formerly used in aerosol sprays,blowing agents for foams, cleaning solvents,and as refrigerants in air conditioners. But inthe 1980s, a hole was discovered in the ozonelayer over Antarctica, and CFCs were deter-mined to be the culprit. The ozone layer lies in the stratosphere, which is about 15 km to
40 km above Earth. Ozone absorbs a type ofultraviolet light, UVB, which is harmful to liv-ing organisms. UVB causes skin cancers andcataracts, as well as damage to some marineorganisms and plants.
In 1987, an international agreement wassigned by 27 nations requiring industrializedcountries to cut their production of CFCs in half before the year 2000. Exemptions were approved for production of CFCs indeveloping countries.
Scientific SolutionsMany substitutes for CFCs already exist. Effortsare being made to find more substitutes and toconstruct equipment that doesn’t rely on CFCs.In Arizona, for example, scientists are workingon an air conditioner that uses freshwater andsalt water as its working fluids.
In refrigerators, CFCs circulate in pipesinside the refrigerator and also are part of thefoam insulation used in the outside shell. Man-ufacturers are interested in tetrafluoroethaneand other substitutes for CFCs, but they needmore than CFC replacements to meet efficiencyrequirements. New insulation ideas includeusing silica gels, silica powders, stainless-steelsheets with glass beads between them weldedtogether by a laser, and microfiberglass.
Substitutes for CFCs need to be reviewed bythe Environmental Protection Agency, andinventions will have to be tested. Scientists hopethat new methods will be developed to protectthe ozone layer.
Applying Critical Thinking Skills1. The 1987 international agreement was based partly on the assumption that industrialized nations
produced a much greater amount of CFCs than less-industrialized nations. That was one of thereasons the agreement required industrialized nations to cut their production of hydrocarbons,but didn’t require less-industrialized nations to limit their production. Do you think that was agood agreement? Explain.
2. Suppose you’re an engineer with an idea for a new air conditioner. What kind of factors shouldyou consider when developing and testing your idea?
While ozone close to Earth’s surface is a pollutant, the ozone layerprotects life on Earth.
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Snowball Earth
Rocks deposited by glaciers can be found allover the world, even in tropical areas. This facthas led some scientists to hypothesize thatEarth, at some time, might have been com-pletely frozen. Evidence shows that a totalglobal freeze might have happened as many asfour or even five times. Scientists call theseglobal freezes “Snowball Earth” and believe thatthey most likely occurred between 580 millionand 750 million years ago.
Why did Earth freeze?One possible explanation for why this hap-pened lies with the plate tectonics theory.According to this theory, the same forces underEarth’s surface that cause earthquakes and vol-canoes cause the continental plates to movearound. The continents have moved togetherand moved apart and are, in fact, still moving.
Before Snowball Earth, the continents wereone giant continent, located near the equator.The continent’s interior, far away from theoceans, was dry. Then, this large continentbroke into three pieces, still near the equator.Now, however, the interiors of the continentswere much closer to the oceans, causing rain tofall. The increased rainfall caused more carbondioxide to wash out of the air, causing Earth’stemperatures to drop, and ice sheets to form inthe polar regions.
As huge polar ice sheets grew larger, their glar-ing white surfaces reflected the Sun’s heat awayfrom Earth, making temperatures fall even more.Once ice had covered half of Earth’s surface, so
much of the Sun’s radiation was deflected, thattemperatures on Earth plunged. This caused theice sheets to grow even larger, until they coveredEarth and its oceans completely.
14Activity
ProblemSolving
Applying Problem Solving Skills1. During a global freeze, volcanoes would have continued to erupt. Volcanoes emit carbon dioxide,
a greenhouse gas. Usually, evaporating moisture absorbs some carbon dioxide in the air. Watervapor also raises temperatures. How do you think this process would have changed with icesheets covering all of the oceans?
2. Albedo is a measurement of the amount of radiation from the Sun that reflects off a surface. Ahigher albedo indicates that more radiation is reflected, meaning surface temperatures are lower.Note the albedos for the following surfaces: new pavement, 0.04; seawater, 0.10; forest, 0.14; drydesert, 0.37; sea ice, 0.60; and snow on ice, 0.80. Considering the effect that large ice sheets haveon Earth’s climate, what do you think the effect would be if dry deserts were paved over? Explain.
Calciumcarbonates
Crystalfans
Glacialdeposits
Layers of rock in the Rocky Cliffs on the Skeleton Coast in Namibia,in southwestern Africa, provide evidence of a global freeze andrapid warming afterward. Calcium carbonates usually form inwarm seas but not in glaciers. They indicate Earth did freeze, evennear the equator, and then warmed up rapidly.
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15ActivityThe Ocean—An Abundant
Source of SaltCriticalThinking
Much of Earth’s surface is covered by water, but94 percent of it is salt water. Because there is alack of freshwater in parts of the world, such asthe Middle East and the Caribbean, scientistshave developed methods for using salt waterfrom the ocean for drinking water. This process,called desalination, removes salt from water.
Desalination ProcessesDistillation is one of the oldest methods ofdesalination. Seawater is boiled to produce puresteam. The steam is cooled until it condenses and runs as pure water. Distillation has been useful at sea. U.S. Navy cruisers had distillationplants on board in World War II. A more modernversion of distillation is freeze distillation. Freezedistillation removes salt and impurities fromwater by freezing it.
Electrodialysis is a process that uses an electriccurrent to move salt ions through a membrane,leaving freshwater behind. It works well withbrackish groundwater, because brackish waterhas a lower salt concentration than seawater.
Reverse osmosis is a pressure-driven process.Pressure is used to separate the freshwater,which passes through a membrane, from thesalts, which do not. Reverse osmosis also worksbetter with brackish water.
The most recent development in desalinationtechniques is ocean thermal energy conversionor OTEC. Keahole Point on the island ofHawaii has become one of the world’s foremostlaboratories and test facilities for OTEC tech-nologies. Because the layers of ocean water havedifferent temperatures, OTEC uses the ocean’stemperature differences to produce energy. Thismethod could provide areas, such as tropicalisland communities, with power as well as withdesalinated water.
Environmental and Economic ConcernsDesalinating water has negative effects on theenvironment. The leftover salt solution mightkill marine life when it is returned to the ocean.Incoming salt water might be treated with abiocide, such as chlorine, to remove algae andbacteria. These chemicals need to be treatedprior to being released into the ocean.
Another disadvantage to desalination is that most of the processes are expensive to perform. Distillation costs are high due to the energy that is needed to heat the water.Reverse osmosis and electrodialysis are cheaperprocesses because they require less energy,but the membranes have short lives and areexpensive to replace.
Although there are currently many processesfor desalinating water, scientists continue towork on improving these methods. The needfor low-cost desalination methods will alwaysbe in great demand for arid areas of the world.
Applying Critical Thinking Skills1. Why are there so many different processes for desalination? What are scientists looking for?
2. Do you think that the need for desalination will increase or decrease in the next century? Givereasons for your answer.
Solar energy can be used to desalinate water.
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The Mysterious Eel
Eels are a snakelike fish that breed in the oceanbut feed and grow in freshwater. To do this, theymust migrate. Early scientists were puzzled bythe eels’ migration patterns. Europeans, forinstance, found large numbers of adult eels inlakes, streams, and rivers. But no one ever saw ayoung eel or an eel egg.
The Greek philosopher Aristotle suggestedthat eels developed from the mud at the bottomof the lakes. It wasn’t until 1922 that the mys-tery was solved by Danish oceanographerJohannes Schmidt. He found that a particularsmall, flat fish found in the Sargasso Sea wasactually a young eel.
A Moving SeaThe Sargasso Sea is an area of warm and excep-tionally clear water a few hundred kilometerseast of Florida. The Sargasso Sea drifts, and its location is determined by the changing,
clockwise-flowing ocean currents that form itsperimeter. Here, about 600 m beneath the sur-face of the ocean, American and European eelsproduce and fertilize eggs. Tiny, transparent lar-vae hatch from these eggs. These tiny life-formsare then carried northward by ocean currents.Some are caught by currents that move up theeast coast of the United States and enter fresh-water rivers where they live and feed. Others arecarried by the Gulf Stream across the AtlanticOcean to Europe.
The Eels’ Life CycleDuring their drifting migration, which can take three or four years, the larvae of the European eels develop into larger, leaf-shapedlarvae that feed on plankton. When they finallyreach the shallow ocean waters near land, theybecome young eels and move into the freshwa-ter rivers along the coastline. In freshwater, theyfeed and grow.
Eels can remain in freshwater from five toten years, although eels 20 years old have beenreported. An eel takes about ten years to reachmaturity. At this time, it changes to a silverycolor and its eyes grow larger. The mature eelmoves downriver and back to the sea.
The mystery of eels is not solved, though.Adult eels have never been caught in the Sar-gasso Sea. Their breeding, or spawning, behav-ior is still unknown, although it is presumedthat the adult eels die after spawning. Do theyreturn from Europe to the Sargasso Sea? If so,why have none been seen? If not, where do thelarvae in the Sargasso come from?
16Activity
CriticalThinking
Applying Critical Thinking Skills1. Aristotle suggested that eels developed from mud at the bottom of lakes. What type of scientific
evidence could you present to him to prove otherwise?
2. Parts of the life cycle of eels (and other marine animals) are still a mystery. Why does this make itimportant to preserve all marine habitats?
Africa
North America
BermudaAzores
Atlantic Ocean
Sargasso Sea
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17ActivityPlant-Based FuelsCritical
Thinking
Surplus corn and other grains, such as wheat andbarley, can be processed into ethanol. A clear, col-orless liquid, ethanol is used as fuel in internal-combustion engines, such as those found inautomobiles. Ethanol already is blended into mostgasoline sold in the United States. This use ofethanol saves nearly a billion gallons of oil a year.
Biomass EthanolScientists are investigating advanced ways, suchas biomass feedstocks, to produce ethanol. Theterm biomass refers to any organic matter that isrenewable, including wood, crops, plants, andanimal wastes. Biomass feedstocks include cornfiber, plant residue, and rice straw. The feed-stocks contain cellulose, which can be convertedinto sugars that are fermented into ethanol.These biomass feedstocks are considered low- orno-cost waste material.
Using inexpensive resources reduces the cost ofproducing ethanol. Also, using these waste mate-rials has environmental benefits; they otherwisewould be burned or put into a landfill. As an
added bonus, waste materials of the ethanol con-version process are high in protein and othernutrients, making them an excellent feed ingredi-ent for livestock.
SoyDieselBiodiesel fuel is being developed as an alternativeto petroleum for heavy vehicles. This fuel is madefrom natural, renewable sources, such as new orused vegetable oils. It is a cleaner-burning fueland can operate in existing combustion-ignitionengines. Soybean oil and methanol produce aproduct called methyl soyate, or SoyDiesel. Soy-Diesel is the main type of biodiesel fuel used inthe United States. Alternative oils that are beingconsidered are animal fat wastes and used fryingoil, which are cheaper than soybean oil.
MethanolMethanol is another plant-based fuel. It is madefrom wood. Like ethanol, methanol can bemixed with gasoline. Pure methanol, or neatmethanol, is used as a racing fuel. Methanol is a promising hydrogen source for fuel-cell vehicles.
Hydrogen gas also is beingtested for use in combus-tion engines. Because it isa gas instead of liquid, it iseasier to store and trans-port.
Both ethanol andmethanol are renewableresources, which meansthat they can be replaced bynatural processes in lessthan 100 years. Theseclean-burning fuels arepromising fuel alternativesfor the future.
Applying Critical Thinking Skills1. Why do you think some people would be reluctant to change from using gasoline or diesel fuel in
their automobiles to ethanol or methanol?
2. Do you think the United States should continue working toward using renewable agriculturalproducts for fuel energy? Why or why not?
Ethanol Production
LiquefactionMeal is mixed with waterand enzymes and cooked
at 120-150°C, makingmash (liquefied starch).
MillingCorn, barley, or wheat is
ground into meal.
SaccharificationEnzymes are added to
cooled mash, convertingstarches in mash
into sugars.
Distillation and Dehy-dration
Ethanol is separated fromthe water and grains inthe mash, producing
100% ethanol.
DenaturingA small amount of
gasoline is added to the ethanol to make
it undrinkable.
FermentationYeast added to the mash ferments the
sugar into ethanol andcarbon dioxide.
Grains are sold ashighly nutritiouslivestock feed.
Ethanol is ready for use as fuel.
Carbon dioxideis collected for
other uses.
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Efforts to Neutralize Acid Precipitation
Oil- and coal-burning power plants producepollutants. These pollutants, in particular sulfurdioxide and nitrogen oxide, contribute to hazein the air and can cause health problems. Whenthey mix with rain, snow, or fog, they produceacid precipitation. Acid precipitation consists ofsulfuric and nitric acids. It can damage forests,buildings, and monuments, and can acidifylakes and streams.
Reducing Effects of Acid PrecipitationWoods Lake is in the Adirondack Mountains inNew York. In 1989, it was discovered that nofish could live in the lake because it was tooacidic. Acid rain fell on the soil and washedinto streams that flowed into the lake. Scientistswere determined to save the lake. First, theytried putting limestone slurry into the lake.Limestone is a basic material that, when addedto acidic water, makes it neutral. After addingthe limestone, the scientists stocked the lakewith fish, but the fish didn’t live. Rain broughtmore acid into the lake.
Then, scientists dropped large amounts oflimestone pellets by helicopter onto the soilnear Woods Lake. Rain washed the limestoneinto the lake. Acid levels in the lake droppedand rose only slightly after additional rains. Sci-entists estimated that the limestone pelletsshould work for about five years before addi-tional applications were needed.
Preventing Acid PrecipitationIn a 1990 amendment to the Clean Air Act,Congress made a plan to reduce sulfur dioxideand nitrogen oxide emmissions by the year2010. The goal was for companies to reducetheir pollution levels by millions of tons. Thisnew law offered a different approach. It recog-nized that companies would continue to pollute.However, companies that polluted less thantheir allowance could use what was left over as areserve for later or they could trade it to othercompanies who went over their allowances.
Why did Congress take this approach? Mem-bers wanted to solve the pollution problem,while keeping the costs for doing so as low aspossible. It is expensive for companies to reduceemissions. They might have to fix or replaceequipment, or they might even have to changethe way they use fuels. Under the new plan,companies that could afford to reduce theiremissions could reduce pollution to even lowerlevels than required by their allowances. If so,they could trade their allowances to other com-panies that couldn’t afford to meet their owngoals. Overall, the pollution level woulddecrease while costs would be kept down.
This unique approach to reducing emissionsworked. By 1995, sulfur dioxide emissions werealmost 40 percent below target at 445 plants in21 eastern and midwestern states. Nationally,emissions were 20 percent below target.
18Activity
ProblemSolving
Applying Problem Solving Skills1. The problem that concerned scientists studying Woods Lake was that the lake couldn’t support
life. What scientific hypothesis was tested at Woods Lake?
2. One concern with the trading program is that it might reduce pollution in some areas of thecountry, while letting it increase in other areas. Do you think this program is an acceptable way toreduce pollution overall?
3. Why is it difficult to judge the success of a pollution-control program?
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19ActivityThe Pros and Cons of
Gene ModificationProblemSolving
Farmers use many different chemicals to killinsects and weeds that threaten their crops.Chemicals are a concern to many consumersbecause they can contaminate soil and water.Some have been found to cause cancer. Someexperts claim that the disadvantages of pesticidesare overemphasized. Still, scientists search forways to avoid chemical pesticides.
BiotechnologyOne alternative to using pesticides is biotech-nology. Biotechnology is a collection of scien-tific techniques used to create or improveplants, animals, and microorganisms.
In Colorado, the potato beetle had plaguedpotato crops for years. The beetles would eat anentire field of crops, leaving nothing but stems.Rather than using chemical pesticides,researchers invented a “smarter” potato. Theyinserted a gene that changed the DNA of thepotato. It worked as an organic pesticide. Nowthe potato plant contains a biopesticide that isdeadly to the beetle.
Altering the DNA of a plant is called geneticmodification. Approximately 18 millionhectares of American farmland are planted withgenetically modified (GM) crops. This technol-ogy is being studied for use in areas of Asia,Latin America, and Africa where hunger andmalnutrition are epidemic.
Researchers have developed a new rice thatcontains iron and vitamin A and a geneticallyaltered sweet potato that resists a harvest-destroying virus. There is hope that these andother crops can be planted to help prevent mal-nutrition and starvation
Untested WatersDespite the promise of GM plants, some peoplefear the results. One concern is that genes of GMplants might cross-fertilize with wild plants andcreate “super weeds.” These super weeds couldbecome resistant to certain herbicides. Some fearthat mutant bugs might result if pests becomeresistant to the toxic effects of GM crops.
Other concerns are for human safety. Oppo-nents call GM crops “Frankenfood.” They fearthat illnesses could result from eating theseplants. The greatest human health concern isallergies that might result from GM plants.Testing can be performed for known allergens,but new allergens might be created when genesin plants are altered.
Applying Problem Solving Skills1. What are the major problems connected with chemical pesticides?
2. Why do some people anticipate problems with genetic modification?
3. Which type of pesticides—chemical or genetically modified—would you prefer to have used onfoods you eat? Why?
4. Do you think the government should regulate genetic modification? Explain.
A scientific study found that pollen from one variety of GM cornmight kill the caterpillar Danaus plexippus, whichbecomes the monarch butterfly.
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Controlling the Zebra Mussel
In the mid-1980s, a mollusk new to NorthAmerica, the zebra mussel, was found in LakeSt. Clair in Ontario, Canada. Ordinarily, zebramussels live in the seas of northern and westernEurope. They are small, inactive creatures mea-suring just 2.5 to 7.5 cm long and spend theirlives attached to an underwater surface. Theyprobably came here from the Black and Caspianseas by way of ballast water, the seawater used tomaintain the stability of a ship.
A Growing ProblemAt first there were only a few small colonies, butwithin months the mussels expanded throughoutLake St. Clair and into surrounding lakes. Theyspread to Lake Erie and into the other Great Lakes.Zebra mussels have been found in portions of theMississippi, Hudson, Ohio, Illinois, Tennessee,Susquehanna, and Arkansas rivers. They havespread to at least 19 states, including California.
Studies estimate that one female zebra mussel can release one million eggs per year.To survive, they eat large amounts of plankton.Each day, a single adult mussel can consume allof the plankton found in a liter of water.
Other Species SufferWhen enough zebra mussels colonize one area,they leave little or no food for the native animalsthat also live on plankton. This produces a short-age of food for larger fish. Because zebra musselseat most of the plankton, lake water becomesclearer so more light reaches deeper into the lake,causing increases in vegetation such as algae.
Zebra mussels tend to attach themselves toany available surface. Because they multiply sorapidly, they have been found throughoutwater-treatment plants on the Great Lakes,clinging to pipes and machinery. They decreasethe diameter of the pipes’ openings and in somecases cut off the flow of water.
SolutionsSeveral methods exist for removing zebra mus-sels. The safest way is to remove them by hand,but that takes a great deal of time. Some water-treatment plants use jets of steam and hotwater to kill them. Most treatment plants usechlorine. This works, but too much chlorinecan contaminate drinking water. Scientists havebeen testing potassium, bromine, ozone, andultraviolet light as possible alternatives.
In addition, scientists have suggested intro-ducing exotic predators to help control thegrowth of zebra mussels. Another solutionwould be to regulate the spawning of zebramussels. If they could be made to spawn attimes when plankton levels are low, the larvaewould die.
20Activity
ProblemSolving
Applying Problem Solving Skills1. Consider the problem of ridding North America of zebra mussels. Give advantages and disadvan-
tages of each of the methods mentioned. Which method described would you recommend?
2. Ridding the lakes and rivers of zebra mussels will be expensive. Where do you think the moneyfor such a project should come from? Write a statement defending your answer.
Zebra mussels attach to underwater surfaces.
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21ActivityRecycling in SpaceProblem
Solving
You probably have participated in water-savingprojects at home or in your community. Suchprojects usually include taking shorter showers,turning off the tap when not necessary, andreusing dishwater or bathwater to water plantsor the lawn. What if you also had to recycle themoisture in your breath, sweat, or even urine?
Water in SpaceAstronauts on the International Space Station(ISS) have to do just that. In addition, they alsomust reuse the humidity generated by any ani-mals on board, such as lab rats. Although somewater and food supplies will be carried to thestation by shuttle missions, it’s too expensive toship all of the water needed. The Environmen-tal Control and Life Support System (ECLSS)Water Recycling System (WRS) will recyclemost of the water used on board. This will savemore than 18,000 kg of water per year, whichwould otherwise have to be brought in by shut-tle missions.
Purer than Water on EarthOf course, the water you drink on Earth alsocomes partly from recycled breath, sweat, andurine. Wastewater that flows into the groundpasses through the soil, which filters it physi-cally. Microbes in the soil act on organic sub-stances, filtering the water chemically.Waste-water that evaporates into the atmos-phere leaves impurities behind and is convertedto rain—nearly pure freshwater.
On the ISS, machines do the work of all ofthese natural processes. Machines that breakdown can be fixed, unlike microbes, which candie or grow out of control. The system uses
three steps. First, a filter removes particles largerthan water molecules. Then the wastewaterpasses through layers that remove impurities.Finally, a catalytic oxidation reactor removesvolatile organic compounds and kills bacteriaand viruses.
The life-support system is not perfect, how-ever. Over time, water will be lost in severalways. The water-purification system itself willproduce some unusable water as brine, and theair-purification systems will remove somehumidity that could have been transformedinto water. When astronauts go outside the ISS,some air containing humidity will flow outthrough the air locks.
Engineers hope to increase the efficiency ofthe water-purification system to 95 percent.This way, the moisture contained in food sup-plies would replace the other five percent.
Clearing the AirThe ECLSS also purifies the air astronautsbreathe on the ISS. Humans and animalsbreathe in oxygen and breathe out carbon diox-ide. Currently, the system vents CO2 to the out-side. Eventually, engineers hope to recyclecarbon dioxide. Humans and animals also emitsmall amounts of other gases such as ammoniaand methane. Scientific experiments also createvapors that must be removed from the air. Acti-vated charcoal filters will remove these gases.
Where will the oxygen come from? In aprocess called electrolysis, solar panels on the ISS will create electricity which, in turn,splits water into hydrogen gas and oxygen gas. On Earth, this process occurs as part of photosynthesis.
Applying Problem Solving Skills1. How does the method of purifying water on the ISS differ from natural purification methods on Earth?
2. Eventually, engineers hope to use plants in space to create oxygen and filter the air. Why do youthink they now use machines?
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Fighting Off the Winter Blues
When winter approaches and the weather getscolder and the days get shorter, many peopleexperience a noticeable change in their moods.They may oversleep, overeat, or experiencedepression, fatigue, or difficulty concentrating.Although these symptoms can have manycauses, they often are the symptoms of a diseasecalled seasonal affective disorder or SAD.
Who Suffers?It is estimated that 10 million to 25 millionAmericans experience symptoms of SAD. Peo-ple of all ages, occupations, and ethnic groupscan suffer from SAD. Most sufferers, however,are women between the ages of 20 and 50.Almost four times as many women as men suf-fer from the disease.
Some people might have only a mild form ofthe disease. They might feel slightly depressed.They could oversleep and overeat. They mightlack energy. Some people suffer from muchstronger cases of SAD. Some can’t concentrateduring the winter. Some are totally nonproduc-tive, lacking enough energy to do even the sim-plest tasks. They might withdraw from socialcontact and feel depressed constantly.
As winter ends, SAD sufferers begin torecover. Once again, they participate fully intheir daily routines. Yet, year after year, SADsymptoms reappear in winter.
The Light ConnectionScientists are researching the causes of SAD.They think there is a link between SAD and thedecreased amount of daylight available during
the winter. Light affects hormone levels. Somescientists think that it’s this shortness of daylighthours that causes SAD.
Light TherapyResearchers reason that if a lack of light causesSAD, light therapy could help SAD sufferers.Initial studies had groups of SAD patients sit-ting in front of light boxes for several hours aday before dawn and after dusk. The light boxesused a type of fluorescent light that’s similar tothe color range of natural summer sunlight.
The patients began to see positive changes soonafter the treatments started. Their moods began toimprove. They had more energy and felt able tocarry on their everyday activities. The same patientswere exposed to periods of dim light as well. Thedim-light therapy proved to be ineffective.
22Activity
CriticalThinking
Applying Critical Thinking Skills1. People who live in the higher latitudes are more likely to suffer from SAD than people who live in
the lower latitudes. Why do you think this is?
2. SAD patients using light therapy can suffer from side effects such as headache, eyestrain, andsleeplessness. What might be done to reduce these side effects?
Light therapy helps people overcome the effects of SAD.
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23ActivityEarly SkywatchersCritical
Thinking
Many researchers study early peoples and theirknowledge of the Sun, Moon, and stars. Thisfield of study, called archaeoastronomy, focuseson peoples from prehistoric times to the Egyp-tians and Maya.
These scientists have learned that the earlypeople of the Americas were excellentastronomers and builders. The Maya built theoldest known observatory in the western hemi-sphere around A.D. 317. They kept careful recordsof the movements and changes of the Sun andMoon on calendars. Astronomy was the study oftheir gods. To the skywatchers, the apparentmovements of the Sun and Moon gave the godstheir personalities. The events in the sky werereflected in the religion, festivals, art, and archi-tecture of the people.
Machu PicchuAt one site, Machu Picchu in Peru, archaeoas-tronomers study the Incan temple of Torreón.An amazing occurrence takes place there on theJune solstice. Shortly after dawn, the sunlightshines through a window onto a sacred stone.The Inca believed that the Sun god was returningto its home on the June solstice. They held a Sunfestival at that time to pay special honor to theSun god.
TeotihuacanThe Toltec city Teotihuacan lies northeast ofMexico City, Mexico. Teotihuacan was already inruins when the Aztecs ruled central Mexico. TheToltecs arranged their city in a huge, four-partgrid. Within one grid is the great Temple of theSun, which was built over a sacred cave. Its stepsalign with a point on the horizon. Scientistshave found that this point is the place where thePleiades star cluster sets on the horizon.
Chaco CanyonChaco Canyon in New Mexico was probably acultural center to ancestral Puebloan residentsfrom about A.D. 900 through A.D. 1130. Ancientdrawings found in West Mesa, a part of ChacoCanyon, contain three symbols—a large star, acrescent moon, and a print of a hand. Every18.5 years, the Moon and Earth are positionedso that they can be seen from West Mesa. Thefingers of the handprint point to the Moon inthe sky on that day. Archaeoastronomersbelieve that the large star in the drawing is CrabNebula, which was formed during the A.D. 1054supernova. Did the Chacoans see the supernovaand record it in their drawings or is there someother explanation?
Archaeoastronomers are trying to answerthis and many other questions. By studying thedrawings and temples of early peoples, peopletoday might gain a better understanding andappreciation of early skywatchers.
Applying Critical Thinking Skills1. How are the three monuments described in this passage alike?
2. What evidence supports the statement that the early people of the Americas were excellentastronomers and builders?
3. Why do you think scientists are interested in the astronomy of early peoples?
The 1054 supernova rock at Chaco Canyon
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Activity 1 ______________________ page 1Earth’s Last Frontier—Hydrothermal Vents
1. Distinguishing Relevant from IrrelevantFacts: Students should list at least three ques-tions that they would have asked the first sci-entist to see a hydrothermal vent. Questionsmight be related to the vent’s appearance, thelife-forms surrounding it, the methods used tofind it, or any other appropriate subject.
2. Recognizing Cause and Effect: By discoveringthe unique bacteria that were at the base of thefood web, scientists could begin to understandhow this extreme environment could supportso many life-forms.
3. Drawing Conclusions: Answers will vary, butstudents should indicate that hydrothermalvents are Earth’s last frontier because they havenot been fully explored. It has been less than30 years since the vents were first discoveredand exploration has been slow. In comparisonto space exploration, scientists know littleabout this phenomenon.
Activity 2 ________________ page 2Atomic Energy—Good and Bad
1. Drawing Conclusions: Nuclear energy canprovide power for generating electricity, butthe fear of accidents has caused many peopleto object to its use.
2. Making Judgments: Students’ answers mightvary. Students should illustrate an understand-ing of the potential benefits and dangers ofatomic power.
3. Developing a Perspective: Students’ answersmight vary. Students should weigh their con-cerns for safety with the need for power.
Activity 3 ______________________ page 3Phosphates—Help or Hazard?
1. Making Predictions or Interpretations: IfFlorida’s phosphate rock continues to be minedin large amounts, the supply eventually will runlow. The United States will need to find alterna-tive supplies for phosphate fertilizer or an alter-native form of fertilizer.
2. Making Judgments: Students’ answers will vary.Students believing that a federal ban on phos-phates in detergents should have been enactedmight cite its large role in causing pollution, par-ticularly algal blooms in lakes and streams. Stu-dents believing a federal ban should not have beenenacted might state that such a ban should bebased on local or state conditions and thereforeshould be made at the local or state level.
Activity 4 ________________ page 4Rock Solid
1. Classifying: Limestone—sedimentary; granite—igneous; slate and marble—metamorphic; sand-stone—sedimentary. Limestone and sandstonesplit easily because as sedimentary rocks, theyformed in layers. Slate is a foliated metamorphicrock; it formed in layers also. Granite, an igneousrock, and marble, a nonfoliated metamorphicrock, form not in layers but in solid masses; theywould be more difficult to cut.
2. Evaluating Information: Marble would be agood choice for the statue because it can befound in pure white, it carves well, and itstranslucence has made it a valued sculpturematerial in the past. Granite would be a goodchoice for the monument because its surfacecan be polished to a shine.
Activity 5 ________________ page 5Sky-High Views
1. Evaluating Information: A GPS receiver has ahigh resolution. Thus, one computerized data-bank provides enough information to produce detailed local maps of a large area. Thepositions can then be mapped on an electronicmap of choice.
2. Observing and Inferring: It would give thecommander the locations of all the groups’positions at any one time and reduce the timeneeded to redistribute the groups. Aerial pho-tography also might be useful in tracking theexact location of the fire as it spreads.
Answer KeyCritical ThinkingProblem Solving
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3. Comparing and Contrasting: In monitoringfern growth in a dense forest, aerial photogra-phy would not be a good choice because fernsgrow low to the ground and the trees wouldobscure their view.
4. Making Predictions or Interpretations: Stu-dents’ answers might vary. Some potentialapplications might include surveying land forbuilding projects, mapping problem trafficareas, or producing more accurate ocean navi-gation maps.
Activity 6 ________________ page 6Saving the Soil
1. Recognizing Cause and Effect: Dryland farm-ing allows ground left fallow to replenish thenutrients necessary for crops to grow andthrive. It also conserves groundwater.
2. Extrapolating Data/Information: In theUnited States, areas in the Midwest, the north-ern and southern Plains, and the corn belt arepossible answers.
Activity 7 ______________________ page 7Buffering Against Erosion
1. Comparing and Contrasting: Wetlands, grassbuffers, and forest buffers all filter sedimentand chemicals from runoff resulting from rainfall. Wetlands and some forest buffers occurnaturally, but grass pathways and hedges andother forest buffers are planted. Grass buffersand zone two of planted forest buffers can beharvested.
2. Making Judgments: Rain is not the only causeof erosion. The Dust Bowl eroded during adrought, due to wind and poor farming meth-ods. Also, farmers need to control the amountof chemicals that flow into surface andgroundwater with farming techniques in addi-tion to buffers.
3. Making Predictions or Interpretations: Somerunoff ends up in groundwater, which ends up,in many cases, as drinking water, and in othercases as water for crop irrigation. High levels ofsome chemicals in drinking or irrigation watercan be harmful to the humans or livestock thatdrink this water and eat these crops. Otherrunoff ends up in surface water—streams,
rivers, lakes, and the ocean. Chemicals in thiswater can affect fish that humans eat as well asother animals in the water ecosytems.
Activity 8 ________________ page 8Life on Mars?
1. Drawing Conclusions: Ocean bottoms aregenerally smooth because of sediment deposit-ing on the seafloor.
2. Recognizing Cause and Effect: Water is neces-sary for life, and oceans might have been thefirst environments to contain life on Earth.
3. Extrapolating Data/Information: Thereshould be volcanoes and evidence of earth-quakes, as well as mountains.
4. Making Predictions or Interpretations: Thereshould be age evidence, older rock existing far-ther from the fissure point, and the movement ofplates that could be measured.
5. Making a Hypothesis: Students’ answers willvary but will likely suggest finding other areasin which the two planets—Earth and Mars—can be compared.
Activity 9 ______________________ page 9Detecting Earthquake Patterns
1. Making Judgments: Students’ answers will vary.Some students might say that strange animalbehavior frequently has been observed beforeearthquakes occur and could signal other earth-quakes. Other students might suggest that animalbehavior is not a reliable predictor of earth-quakes. Animal behavior could go unobserved orbe related to something other than earthquakes.
2. Making Predictions: Students might note thatthe types of information now available toresearchers and the continued work of scien-tists could lead to accurate short-term predic-tions in the future.
3. Developing a Perspective: Students’ answerswill vary. Some students might conclude thatprediction research is a valid effort that couldsave lives and, therefore, should be funded.Others might think that the money could bebetter used for other projects, such as medicalresearch or social programs.
Answer Key (continued)
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Activity 10 ________________ page 10Energy from Earth
1. Evaluating Information: Hot springs formwhere there’s a lot of groundwater. Mud potsform where there’s some water but not enoughto settle the mud. Fumaroles form wherethere’s just enough water to turn into steam,which forces out gases.
2. Comparing and Contrasting: Students’ answerswill vary but should include some discussion ofenvironmental issues, such as air pollution causedby the burning of coal and land contaminationpossibly caused by the storage of nuclear waste.They also might discuss the relative costs of thethree types of power; hydrothermal and nuclearenergies are renewable and basically free, once thepotentially expensive power plants are built. Coalis not renewable and therefore could becomemore and more expensive, but it would cost lessto keep existing coal power plants than to buildnew nuclear or hydrothermal plants.
Activity 11 ________________ page 11Xenotime Dating
1. Extrapolating Data/Information: Xenotimedating measures the amount of lead in a sam-ple of rock. If lead were to move from onesample of rock to another, xenotime datingwould not be accurate, because a samplewould appear older than it is.
2. Making Predictions or Interpretations: Thetop layer of rock with a higher lead measure-ment of 27 is older than the bottom layerbecause the uranium in the xenotime in therock has had more time to decay, forming morelead than the bottom layer. Although you mightsuspect the older rock to be beneath theyounger rock, tectonic forces in this case musthave forced the older layer above the youngerone.
3. Classifying: In order, the Precambrian era, thePaleozoic era, the Mesozoic era, and the Cenozoicera would have decreasing levels of lead in xeno-time. The older a rock is, the larger the amountof lead in the xenotime within it.
Activity 12 ________________ page 12Birds and Dinosaurs—Related or Not?
1. Classifying: Students’ answers will vary butshould show logical reasoning and be sup-ported by facts. Students might choose someof the following criteria as a basis for classify-ing an animal as a bird: having wings, having abone structure suitable for flight, being warm-blooded, or other traits common to birds.
2. Evaluating Information: Students’ answers willvary but should show logical reasoning. Sampleanswer: The fact that Microraptor was about thesize of a crow, had bones similar in structure tobird bones, and had feathers and toes like birdsmeans that it probably was an ancestor to mod-ern birds. Added to that, the fact that it had manydinosaurlike traits, such as the tail and teeth,means that it probably was a dinosaur. Therefore,birds and dinosaurs are closely related. The factthe Microraptor had feathers even though it couldnot fly indicates that the feathers served anotherpurpose than flight. If the feathers were for insu-lation, then Microraptor, and at least somedinosaurs, were warm-blooded. Finally, the factthat Microraptor had toes that could have graspedtree branches means that birds probably learnedto fly from trees down.
Activity 13 ________________ page 13Keeping the Atmosphere Healthy
1. Examining and Evaluating Assumptions: Stu-dents’ answers will vary. Some might agree thatbecause industrialized nations produce moreCFCs than less industrialized nations, cuttingdown on the amount that they produce willhave a greater impact on the ozone layer. Cuttingdown on the amount of CFCs that less-devel-oped countries use will have much less of aneffect. Others might say that any amount ofCFCs produced reduces the ozone layer, so allcountries should limit production.
2. Assessing Solutions: Students’ answers willvary. Besides the issue of avoiding CFCs, youwould have to consider other environmentalfactors, such as energy efficiency and fuelusage, as well as possible pollution generation.You would need to think about trade-offs: is
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your idea going to avoid one problem and cre-ate others? You don’t want to leave a problemfor future generations to solve. Other consider-ations include cost, space limitations, ease ofmaintenance, and cooling capability.
Activity 14______________________ page 14Snowball Earth
1. Making a Hypothesis: If moisture from theoceans were trapped under huge sheets of ice,no water could have evaporated into the air toabsorb the carbon dioxide emitted by the volca-noes. Carbon dioxide would have built up, rais-ing Earth’s temperatures and melting the ice. Asthe ice melted, the Sun’s light would not bereflected back into the atmosphere as much asbefore, raising temperatures more and meltingmore ice. Water vapor, now able to be releasedinto the air, would also raise temperatures,increasing the rate at which the ice would melt.
2. Extrapolating Data/Information: Because newpavement has a much lower albedo than drydesert, new pavement would reflect less of theSun’s radiation, absorbing it instead. This wouldincrease the surface temperature.
Activity 15 ________________ page 15The Ocean—An Abundant Source of Salt
1. Clarifying Issues: There are many differentprocesses for the desalination of ocean waterbecause no one process is perfect. Scientists arelooking for a process that works and that’s nottoo expensive.
2. Making Predictions: The need for desalinationprobably will increase as populations increase,desertification in some areas continues, andcommercial needs for pure water increase.
Activity 16 ________________ page 16The Mysterious Eel
1. Distinguishing Relevant from Irrelevant Facts:Answers will vary. Students might cite Schmidt’sdiscovery of a baby eel or any other reasonableresponse.
2. Drawing Conclusions: Because parts of theselife cycles are mysteries, the animals mightdepend upon a habitat that scientists mightnot be aware of. The destruction of the habitatcould destroy one or more species.
Activity 17______________________ page 17Plant-Based Fuels
1. Observing and Inferring: Students’ answerswill vary but might include fear of change, notwanting land to be converted from food pro-duction, worries about the expense of the con-version, worries about possible problems withthe new technology, and either lack of knowl-edge about depleting natural resources or dis-belief that resources are limited.
2. Recognizing Cause and Effect: Students’answers will vary but students in favor mightinclude the following points: renewable agricul-tural products are good because they do notdeplete the supply of fossil fuels; they do notpollute as much as gasoline or diesel; and theyprovide another agricultural market. Studentsnot in favor might cite some of the same reasonsas stated in the answer to question 1.
Activity 18 ________________ page 18Efforts to Neutralize Acid Precipitation
1. Observing and Inferring: The hypothesis wasthat adding limestone would neutralize the lake’sacidity.
2. Developing a Perspective: Students’ answerswill vary. Some students might think that it isunfair to cause greater pollution problems inareas that cannot afford to meet their goals andthat pollution must be controlled regardless ofcost. Other students might believe that anyprogram to reduce pollution is worthwhile.
3. Evaluating Information: Students’ answerswill vary. Students might note that it is hard totell whether the program is working if theenvironment takes a long time to show animprovement. The same could be said forhuman health concerns. Students also mightnote that there are many things to judge: envi-ronmental health, human health, damage tobuildings, air pollution, and cost savings.
Activity 19______________________ page 19The Pros and Cons of Gene Modification
1. Clarifying Issues: Known problems withchemical pesticides include water and soil pol-lution and their possible cancer-causing proper-ties.
Answer Key (continued)
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2. Observing and Inferring: Some scientistsanticipate that the newly engineered organismscould increase in number if unchecked anduncontrolled.
3. Drawing Conclusions: Some people will pre-fer the unknown—genetically modified—hop-ing that it’s an improvement. Others will preferthe known danger—chemical—until moreresearch is done.
4. Developing a Perspective: Students’ answerswill vary, but because the release of one organ-ism could have an uncontrolled chain reaction,some regulation seems to be needed.
Activity 20 ________________ page 20Controlling the Zebra Mussel
1. Comparing and Contrasting: Removing themussels by hand is safe but time-consumingand would therefore cost a great deal. Hotsteam is effective and safe but doesn’t solve themain problem. Chlorination is effective andsafe if carefully controlled. Excessive chlorina-tion could harm drinking water. More testingwill need to be performed to determinewhether potassium, bromine, ozone, and ultra-violet light are feasible alternatives. Introduc-ing exotic predators could remove zebramussels but might introduce more problems.Utilizing naturally occurring fish is more sen-sible. Trying to regulate spawning would slowgrowth but might introduce chemicals thatcould cause other problems.
2. Assessing Solutions: Students’ answers willvary. A possible solution is to increase the costof water for consumers. Another possible solu-tion is government assistance.
Activity 21______________________ page 21Recycling in Space
1. Comparing and Contrasting: On Earth, wateris purified when it flows through soil andwhen it evaporates and condenses. On the ISS,machines filter water in a three-step filteringprocess. The process on Earth takes place natu-rally and over some time. Astronauts can moreclosely monitor the machine filtering process.Machines can be fixed, but microbes could dieor grow out of control.
2. Observing and Inferring: Plants take upspace. The number of plants needed to createenough oxygen to sustain an entire flight crewover time would probably take up more roomthan a machine and operate more slowly. Also,plants must be watered, fed, and otherwisecared for. This would be time-consuming.
Activity 22______________________ page 22Fighting Off the Winter Blues
1. Recognizing Cause and Effect: In higher lati-tudes, the number of daylight hours duringwinter is less than the number in the lower lat-itudes. As a result, people are exposed to lowerlight levels. SAD patients would be affected.
2. Generating Solutions: The number of hoursduring which the patient is exposed to thelight could be reduced. This might reduce theside effects.
Activity 23______________________ page 23Early Skywatchers
1. Comparing and Contrasting: The monumentswere all made by early people in the Americas,and all have some connection to astronomicalevents.
2. Distinguishing Relevant from IrrelevantFacts: Students’ answers will vary. Studentsshould point out the accuracy with which thebuilders and painters recorded the alignmentsof solstices, equinoxes, and supernovas. Mea-surements were so exact that features still alignwith astronomical events after centuries havepassed.
3. Drawing Conclusions: Students’ answers willvary. Students should point out that astron-omy influenced religion, festivals, and howcities were built, and therefore reveals muchabout the lives of early people. Scientists alsomight be able to identify changes that occurredin the solar system since that period.
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