2012年11月3日雅思阅读机经A类.docx

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1、考试日期：2012年11月3日ReadingPassage1Title:ThedinosaursfootprintsandextinctionQuestiontypes:YES/NO/NOTGIVEN,Summary文章内容回顾文章从恐龙的脚印开始讲恐龙的灭绝。英文原文阅读MassExtinctionsCasesinwhichmanyspeciesbecomeextinctwithinageologicallyshortintervaloftimearecalledmassextinctions.Therewasonesucheve

2、ntattheendoftheCretaceousperiod(around70millionyearsago).Therewasanother,evenlarger,massextinctionattheendofthePermianperiod(around250millionyearsago).ThePermianeventhasattractedmuchlessattentionthanothermassextinctionsbecausemostlyunfamiliarspeciesperishedatthattime.T

3、hefossilrecordshowsatleastfivemassextinctionsinwhichmanyfamiliesofmarineorganismsdiedout.Theratesofextinctionhappeningtodayareasgreatastheratesduringthesemassextinctions.Manyscientistshavethereforeconcludedthatasixthgreatmassextinctioniscurrentlyinprogress.Whatcouldcau

4、sesuchhighratesofextinction?Thereareseveralhypotheses,includingwarmingorcoolingofEarth,changesinseasonalfluctuationsoroceancurrents,andchangingpositionsofthecontinents.Biologicalhypothesesincludeecologicalchangesbroughtaboutbytheevolutionofcooperationbetweeninsectsandf

5、loweringplantsorofbottom-feedingpredatorsintheoceans.Someoftheproposedmechanismsrequiredaverybriefperiodduringwhichallextinctionssuddenlytookplace;othermechanismswouldbemorelikelytohavetakenplacemoregradually,overanextendedperiod,oratdifferenttimesondifferentcontinents

6、.Somehypothesesfailtoaccountforsimultaneousextinctionsonlandandintheseas.Eachmassextinctionmayhavehadadifferentcause.Evidencepointstohuntingbyhumansandhabitatdestructionasthelikelycausesforthecurrentmassextinction.AmericanpaleontologistsDavidRaupandJohnSepkoski,whohave

7、studiedextinctionratesinanumberoffossilgroups,suggestthatepisodesofincreasedextinctionhaverecurredperiodically,approximatelyevery26millionyearssincethemid-Cretaceousperiod.ThelateCretaceousextinctionofthedinosaursandammonoidswasjustoneofthemoredrasticinawholeseriesofsu

8、chrecurrentextinctionepisodes.Thepossibilitythatmassextinctionsmayrecurperiodicallyhasgivenrisetosuchhypothesesasthat