托福TPO33阅读Passage3原文文本+题目+答案解析

　　为了帮助大家高效备考托福，为大家带来托福TPO33阅读Passage3原文文本+题目+答案解析，希望对大家备考有所帮助。　　ExtinctionEpisodesofthePast　　【1】ItwasnotuntiltheCambrianperiod,beginningabout600millionyearsago,thatagreatproliferationofmacroscopicspeciesoccurredonEarthandproducedafossilrecordthatallowsustotracktheriseandfallofbiodiversity.SincetheCambrianperiod,biodiversityhasgenerallyrisen,buttherehavebeensomenotableexceptions.Biodiversitycollapseddramaticallyduringatleastfiveperiodsbecauseofmassextinctionsaroundtheglobe.Thefivemajormassextinctionsreceivemostoftheattention,buttheyareonlyoneendofaspectrumofextinctionevents.Collectively,morespecieswentextinctduringsmallereventsthatwerelessdramaticbutmorefrequent.Thebestknownofthefivemajorextinctionevents,theonethatsawthedemiseofthedinosaurs,istheCretaceous-Tertiaryextinction.　　【2】Startingabout280millionyearsago,reptileswerethedominantlargeanimalsinterrestrialenvironments.Inpopularlanguagethiswastheera“whendinosaursruledEarth,”whenawidevarietyofreptilespeciesoccupyingmanyecologicalniches.However,nogrouporspeciescanmaintainitsdominanceindefinitely,andwhen,afterover200millionyears,theageofdinosaurscametoadramaticendabout65millionyearsago,mammalsbegantoflourish,evolvingfromrelativelyfewtypesofsmallterrestrialanimalsintothemyriadofdiversespecies,includingbatsandwhales,thatweknowtoday.PaleontologistslabelthispointinEarth’shistoryastheendoftheCretaceousperiodandthebeginningoftheTertiaryperiod,oftenabbreviatedastheK-Tboundary.Thistimewasalsomarkedbychangesinmanyothertypesoforganisms.Overall,about38percentofthefamiliesofmarineanimalswerelost,withpercentagesmuchhigherinsomegroupsAmmonoidmolluskswentfrombeingverydiverseandabundanttobeingextinct.Anextremelyabundantsetofplanktonicmarineanimalscalledforaminiferalargelydisappeared,althoughtheyreboundedlater.Amongplants,theK-Tboundarysawasharpbutbriefriseintheabundanceofprimitivevascularplantssuchasferns,clubmosses,horsetails,andconifersandothergymnosperms.Thenumberoffloweringplants(angiosperms)wasreducedatthistime,buttheythenbegantoincreasedramatically.　　【3】Whatcausedthesechanges?Formanyyearsscientistsassumedthatacoolingoftheclimatewasresponsible,withdinosaursbeingparticularlyvulnerablebecause,likemodernreptiles,theywereectothermic(dependentonenvironmentalheat,orcold-blooded).Itisnowwidelybelievedthatatleastsomespeciesofdinosaurshadametabolicratehighenoughforthemtobeendotherms(animalsthatmaintainarelativelyconsistentbodytemperaturebygeneratingheatinternally).Nevertheless,climaticexplanationsfortheK-Textinctionarenotreallychallengedbytheideasthatdinosaursmayhavebeenendothermic,becauseevenendothermscanbeaffectedbyasignificantchangeintheclimate.　　【4】ExplanationsfortheK-Textinctionwererevolutionizedin1980whenagroupofphysicalscientistsledbyLuisAlvarezproposedthat65millionyearsagoEarthwasstuckbya10-kilometer-widemeteoritetravelingat90,000kilometersperhour.TheybelievedthatthisimpactgeneratedathickcloudofdustthatenvelopedEarth,shuttingoutmuchoftheincomingsolarradiationandreducingplantphotosynthesistoverylowlevels.Short-termeffectsmighthaveincludedhugetidalwavesandextensivefires.Inotherwords,aseriesofeventsarisingfromasinglecataclysmiceventcausedthemassiveextinctions.Initially,themeteoritetheorywasbasedonasinglelineofevidence.Atlocationsaroundtheglobe,geologistshadfoundanunusuallyhighconcentrationofiridiuminthelayerofsedimentaryrocksthatwasformedabout65millionyearsago.IridiumisanelementthatisusuallyuncommonnearEarth’ssurface,butitisabundantinsomemeteorites.Therefore,AlvarezandhiscolleaguesconcludedthatitwaslikelythattheiridiuminsedimentaryrocksdepositedattheK-Tboundaryhadoriginatedinagiantmeteoriteorasteroid.Mostscientistcametoacceptthemeteoritetheoryafterevidencecametolightthatacircularformation,180kilometersindiameterindiameterandcenteredonthenorthcoastoftheYucatanPeninsula,wascreatedbyameteoriteimpactabout65millionyearsago.　　1.Thewordproliferationinthepassage(paragraph1)isclosestinmeaningto　　A.decline.　　B.extinction.　　C.increase.　　D.migration.　　2.Paragraph1supportswhichofthefollowingstatementsaboutlifeonEarthbeforetheCambrianperiod?　　A.Biodiversitylevelsweresteady,asindicatedbythefossilrecord.　　B.Levelsofbiodiversitycouldnotbetracked.　　C.Themostdramaticextinctionepisodeoccurred.　　D.Fewmicroscopicspeciesexisted.　　3.Whichofthesentencesbelowbestexpressestheessentialinformationinthehighlightedsentenceinthepassage?Incorrectchoiceschangethemeaninginimportantwaysorleaveoutessentialinformation.　　A.Thedominanceofdinosaurscametoanend65millionyearsago,atwhichtimemammalsbegantoflourishanddiversify.　　B.Becausenogroupofspeciescanremaindominantforever,mammalsbecamethedominantgroupwhendinosaursbecameextinct.　　C.Afterbeingthedominantgroupformorethan200millionyears,theageofdinosaurscametoadramaticend65millionyearsago.　　D.Thediversegroupofmammalsthatweknowtoday,includingbatsandwhales,evolvedfromsmallterrestrialformsthathadbeendominatedbydinosaurs.　　4.Accordingtoparagraph2,whyaredinosaurspopularlysaidtohaveruledEarthduringtheCretaceousperiod?　　A.Dinosaursweretheonlyspeciesofreptilethatexistedduring