托福阅读理解-文档.doc

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1、Theoceanbottom，aregionnearly2.5timesgreaterthanthetotallandareaoftheEarth，iseventodaylargelyunexplored.Untilaboutacenturyago，thedeep-oceanfloorwascompletelyinaccessibleandhiddenbeneathwatersaveragingover3，600metersdeep.Totallywithoutlightandsubjecte

2、dtointensepressureshundredsoftimesgreaterthanattheEarth'ssurface，thedeep-oceanbottomisastrangeenvironmenttohumans，insomewaysasforbiddingandremoteastheouterspace. Althoughresearchershavetakensamplesofdeep-oceanrocksforovera century，thefirstdetailedglo

3、balstudyoftheoceanbottomdidnotactuallystartuntil1968，withthebeginningoftheNationalScienceFoundation'sDeepSeaDrillingProject(DSDP).Usingtechniquesfirstdevelopedfortheoffshoreoilandgasindustry，theDSDP'sdrillship，theGlomarChallenger，wasabletomaintainast

4、eadypositionontheocean'ssurfaceanddrillinverydeep waters，takingsamplesofrockfromtheoceanfloor. TheGlomarChallengercompleted96voyagesina15-year-researchprogramthatendedinNovember1983.Duringthistime，itsailed600，000kilometersandtookalmost 20，000sampleso

5、frocksaroundtheworld.Thosesampleshaveallowedgeologiststoreconstructwhattheplanetlookedlikehundredsofmillionsofyearsagoandtomakeoutwhat itwillprobablylooklikemillionsofyearsinthefuture.Today，largelyonthestrengthofevidencegatheredduringtheGlomarChallen

6、ger'svoyages，nearlyallearthscientistsagreeonthetheoriesofplatetectonics(构造学)andcontinentaldriftthatexplainsmanyofthegeologicalprocesses. ThesamplesofrocksdrilledbytheGlomarChallengerhavealsoprovidedaclimaticrecordstretchingbackhundredsofmillionsofye

7、ars.Theinformationof pastclimaticchangescanbeusedtopredictfutureclimates. BasictoanyunderstandingofCanadainthe20yearsaftertheSecondWorldWaristhecountry'simpressivepopulationgrowth.ForeverythreeCanadiansin1945,therewereoverfivein1966.InSeptember1966Ca

8、nada'spopulationpassedthe20millionmark.Mostofthissurginggrowthcamefromnaturalincrease.Thedepressionofthe1930'sandthewarhadheldbackmarriages,andthecatching-upprocessbeganafter1945.Thebabyboomcontinuedthroughthedecadeofthe1950's,producingapopulationinc