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1、打造最大的国内教育平台更多试题请访问http://www.ezhiol.com下载SECTIONI Time35minutes27Questions Directions:Eachpassageinthissectionisfollowedbyagroupofquestionstobeansweredonthebasisofwhatisstatedorimpliedinthepassage.Forsomeofthequestions,morethanoneofthechoicescouldconceivablyanswerthe
2、question.However,youaretochoosethebestanswer,thatis,theresponsethatmostaccuratelyandcompletelyanswersthequestion,andblackenthecorrespondingspaceonyouranswersheet. Untilthe1980s,mostscientistsbelievedthatnoncatastrophicgeologicalprocessescausedtheextinctionofdinosaurst
3、hatoccurredapproximately66millionyearsago,attheendoftheCretaceousperiod.Geologistsarguedthatadramaticdropinsealevelcoincidedwiththeextinctionofthedinosaursandcouldhavecausedtheclimaticchangesthatresultedinthisextinctionaswellastheextinctionofmanyoceanspecies. Thisview
4、wasseriouslychallengedinthe1980sbythediscoveryoflargeamountsofiridiuminalayerofclaydepositedattheendoftheCretaceousperiod.BecauseiridiumisextremelyrareinrocksontheEarth’ssurfacebutcommoninmeteorites,researcherstheorizedthatitwastheimpactofalargemeteoritethatdramaticall
5、ychangedtheearth’sclimateandthustriggeredtheextinctionofthedinosaurs. Currentlyavailableevidence,however,offersmoresupportforanewtheory,thevolcanic-eruptiontheory.AvasteruptionoflavainIndiacoincidedwiththeextinctionsthatoccurredattheendoftheCretaceousperiod,andtherele
6、aseofcarbondioxidefromthisepisodeofvolcanismcouldhavecausedtheclimaticchangeresponsibleforthedemiseofthedinosaurs.SuchoutpouringsoflavaarecausedbyinstabilityinthelowestlayeroftheEarth’smantle,locatedjustabovetheEarth’score.Astherockthatconstitutesthislayerisheatedbythe
7、Earth’score,itbecomeslessdenseandportionsofiteventuallyescapeupwardasblobsormoltenrock,called“diapirs,”thatcan,undercertaincircumstances,eruptviolentlythroughtheEarth’scrust. Moreover,thevolcanic-eruptiontheory,liketheimpacttheory,accountsforthepresenceofiridiuminsedi
8、mentarydeposits;italsoexplainsmattersthatthemeteorite-impacttheorydoesnot.AlthoughiridiumisextremelyrareontheEarth’ss
