美国法学院入学考试LSAT阅读真题4含答案文档格式.docx

美国法学院入学考试LSAT阅读真题4含答案文档格式.docx

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SECTIONI

　　Time35minutes27Questions

　　Directions:

Eachpassageinthissectionisfollowedbyagroupofquestionstobeansweredonthebasisofwhatisstatedorimpliedinthepassage.Forsomeofthequestions,morethanoneofthechoicescouldconceivablyanswerthequestion.However,youaretochoosethebestanswer,thatis,theresponsethatmostaccuratelyandcompletelyanswersthequestion,andblackenthecorrespondingspaceonyouranswersheet.

　　Untilthe1980s,mostscientistsbelievedthatnoncatastrophicgeologicalprocessescausedtheextinctionofdinosaursthatoccurredapproximately66millionyearsago,attheendoftheCretaceousperiod.Geologistsarguedthatadramaticdropinsealevelcoincidedwiththeextinctionofthedinosaursandcouldhavecausedtheclimaticchangesthatresultedinthisextinctionaswellastheextinctionofmanyoceanspecies.

　　Thisviewwasseriouslychallengedinthe1980sbythediscoveryoflargeamountsofiridiuminalayerofclaydepositedattheendoftheCretaceousperiod.BecauseiridiumisextremelyrareinrocksontheEarth’ssurfacebutcommoninmeteorites,researcherstheorizedthatitwastheimpactofalargemeteoritethatdramaticallychangedtheearth’sclimateandthustriggeredtheextinctionofthedinosaurs.

　　Currentlyavailableevidence,however,offersmoresupportforanewtheory,thevolcanic-eruptiontheory.AvasteruptionoflavainIndiacoincidedwiththeextinctionsthatoccurredattheendoftheCretaceousperiod,andthereleaseofcarbondioxidefromthisepisodeofvolcanismcouldhavecausedtheclimaticchangeresponsibleforthedemiseofthedinosaurs.SuchoutpouringsoflavaarecausedbyinstabilityinthelowestlayeroftheEarth’smantle,locatedjustabovetheEarth’score.AstherockthatconstitutesthislayerisheatedbytheEarth’score,itbecomeslessdenseandportionsofiteventuallyescapeupwardasblobsormoltenrock,called“diapirs,”thatcan,undercertaincircumstances,eruptviolentlythroughtheEarth’scrust.

　　Moreover,thevolcanic-eruptiontheory,liketheimpacttheory,accountsforthepresenceofiridiuminsedimentarydeposits;

italsoexplainsmattersthatthemeteorite-impacttheorydoesnot.AlthoughiridiumisextremelyrareontheEarth’ssurface,thelowerregionsoftheEarth’smantlehaveroughlythesamecompositionasmeteoritesandcontainlargeamountsofiridium,whichinthecaseofadiapireruptionwouldprobablybeemittedasiridiumhexafluoride,agasthatwoulddispersemoreuniformlyintheatmospherethantheiridium-containingmatterthrownoutfromameteoriteimpact.Inaddition,thevolcanic-eruptiontheorymayexplainwhytheendoftheCretaceousperiodwasmarkedbyagradualchangeinsealevel.Fossilrecordsindicatethatforseveralhundredthousandyearspriortotherelativelysuddendisappearanceofthedinosaurs,theleveloftheseagraduallyfell,causingmanymarineorganismstodieout.ThischangeinsealevelmightwellhavebeentheresultofadistortionintheEarth’ssurfacethatresultedfromthemovementofdiapirsupwardtowardtheEarth’scrust,andthemorecataclysmicextinctionofthedinosaurscouldhaveresultedfromtheexplosivevolcanismthatoccurredasmaterialfromthediapirseruptedontotheEarth’ssurface.

　　1.Thepassagesuggeststhatduringthe1980sresearchersfoundmeteoriteimpactaconvincingexplanationfortheextinctionofdinosaurs,inpartbecause

　　（A）earliertheorieshadfailedtoaccountforthegradualextinctionofmanyoceanspeciesattheendoftheCretaceousperiod

　　（B）geologistshad,upuntilthattime,underestimatedtheamountofcarbondioxidethatwouldbereleasedduringanepisodeofexplosivevolcanism

　　（C）ameteoritecouldhaveservedasasourceoftheiridiumfoundinalayerofclaydepositedattheendoftheCretaceousperiod

　　（D）notheoryrelyingonpurelygeologicalprocesseshad,upuntilthattime,explainedthecauseoftheprecipitousdropinsealevelthatoccurredattheendoftheCretaceousperiod

　　（E）theimpactofalargemeteoritecouldhaveresultedinthereleaseofenoughcarbondioxidetocauseglobalclimaticchange

　　2.Accordingtothepassage,thelowerregionsoftheEarth’smantlearecharacterizedby

　　（A）acompositionsimilartothatofmeteorites

　　（B）theabsenceofelementsfoundinrocksontheEarth’scrust

　　（C）agreaterstabilitythanthatoftheupperregions

　　（D）thepresenceoflargeamountsofcarbondioxide

　　（E）auniformlylowerdensitythanthatoftheupperregions

　　3.ItcanbeinferredfromthepassagethatwhichoneofthefollowingwastrueofthelavathateruptedinIndiaattheendoftheCretaceousperiod?

　　（A）ItcontainedlesscarbondioxidethandidthemeteoritesthatwerestrikingtheEarth’ssurfaceduringthatperiod.

　　（B）It