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1、智课网托福备考资料托福阅读――地质地貌类（五）In1970geologistsKennethJ.HsuandWilliamB.F.RyanwerecollectingresearchdatawhileaboardtheoceanographicresearchvesselGlomarChallenger.AnobjectiveofthisparticularcruisewastoinvestigatetheflooroftheMediterraneanandtoresolvequestionsab
2、outitsgeologichistory.Onequestionwasrelatedtoevidencethattheinvertebratefauna(animalswithoutspines)oftheMediterraneanhadchangedabruptlyabout6millionyearsago.Mostoftheolderorganismswerenearlywipedout,althoughafewhardyspeciessurvived.Afewmanagedtomigrat
3、eintotheAtlantic.Somewhatlater,themigrantsreturned,bringingnewspecieswiththem.Whydidthenearextinctionandmigrationsoccur?AnothertaskfortheGlomarChallenger’sscientistswastotrytodeterminetheoriginofthedomelikemassesburieddeepbeneaththeMediterraneanseaflo
4、or.Thesestructureshadbeendetectedyearsearlierbyecho-soundinginstruments,buttheyhadneverbeenpenetratedinthecourseofdrilling.WeretheysaltdomessuchasarecommonalongtheUnitedStatesGulfCoast,andifso,whyshouldtherehavebeensomuchsolidcrystallinesaltbeneaththe
5、flooroftheMediterranean?Withquestionsuchastheseclearlybeforethem,thescientistsaboardtheGlomarChallengerprocessedtotheMediterraneantosearchfortheanswers.OnAugust23,1970,theyrecoveredasample.Thesampleconsistedofpebblesofhardenedsedimentthathadoncebeenso
6、ft,deep-seamud,aswellasgranulesofgypsumandfragmentsofvolcanicrock.Notasinglepebblewasfoundthatmighthaveindicatedthatthepebblescamefromthenearbycontinent.Inthedaysfollowing,samplesofsolidgypsumwererepeatedlybroughtondeckasdrillingoperationspenetratedth
7、eseafloor.Furthermore,thegypsumwasfoundtopossesspeculiaritiesofcompositionandstructurethatsuggestedithadformedondesertflats.Sedimentaboveandbelowthegypsumlayercontainedtinymarinefossils,indicatingopen-oceanconditions.Astheydrilledintothecentralanddeep
8、estpartoftheMediterraneanbasin,thescientiststooksolid,shiny,crystallinesaltfromthecorebarrel.Interbeddedwiththesaltwerethinlayersofwhatappearedtobewindblownsilt.Thetimehadcometoformulateahypothesis.Theinvestigatorstheorizedthatabout20millionye
