托福阅读理解_文档

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

2、anattheEarth'ssurface，thedeep-oceanbottomisastrangeenvironmenttohumans，insomewaysasforbiddingandremoteastheouterspace. Althoughresearchershavetakensamplesofdeep-oceanrocksforovera century，thefirstdetailedglobalstudyoftheoceanbottomdidnotactuallystartuntil1968，withthebeginningoftheNationalScienceFo

3、undation'sDeepSeaDrillingProject(DSDP).Usingtechniquesfirstdevelopedfortheoffshoreoilandgasindustry，theDSDP'sdrillship，theGlomarChallenger，wasabletomaintainasteadypositionontheocean's学习参考.....surfaceanddrillinverydeep waters，takingsamplesofrockfromtheoceanfloor. TheGlomarChallengercompleted96voyag

4、esina15-year-researchprogramthatendedinNovember1983.Duringthistime，itsailed600，000kilometersandtookalmost 20，000samplesofrocksaroundtheworld.Thosesampleshaveallowedgeologiststoreconstructwhattheplanetlookedlikehundredsofmillionsofyearsagoandtomakeoutwhat itwillprobablylooklikemillionsofyearsinthef

5、uture.Today，largelyonthestrengthofevidencegatheredduringtheGlomarChallenger'svoyages，nearlyallearthscientistsagreeonthetheoriesofplatetectonics(构造学)andcontinentaldriftthatexplainsmanyofthegeologicalprocesses. ThesamplesofrocksdrilledbytheGlomarChallengerhavealsoprovidedaclimaticrecordstretchingba

6、ckhundredsofmillionsofyears.Theinformationof pastclimaticchangescanbeusedtopredictfuture学习参考.....climates. BasictoanyunderstandingofCanadainthe20yearsaftertheSecondWorldWaristhecountry'simpressivepopulationgrowth.ForeverythreeCanadiansin1945,therewereoverfivein1966.InSeptember1966Canada'spopulatio

7、npassedthe20millionmark.Mostofthissurginggrowthcamefromnaturalincrease.Thedepressionofthe1930'sandthewarhadheldbackmarriages,andthecatching-upprocessbeganafter1945.Thebabyboomcontinuedthroughthedecadeofthe1950's,