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托福TPO15阅读Passage2原文文本+题目+答案解析.pdf

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¡¡¡¡ÎªÁË°ïÖú´ó¼Ò¸ßЧ±¸¿¼Íи££¬Îª´ó¼Ò´øÀ´Íи£TPO15ÔĶÁPassage2Ô-ÎÄÎı¾+ÌâÄ¿+´ð°¸½ âÎö£¬Ï£Íû¶Ô´ó¼Ò±¸¿¼ÓÐËù°ïÖú¡£ ¡¡¡¡¨Íи£TPO15ÔĶÁPassage2Ô-ÎÄÎı¾£º ¡¡¡¡MassExtinctions ¡¡¡¡Casesinwhichmanyspeciesbecomeextinctwithinageologicallyshortinterval oftimearecalledmassextinctions.Therewasonesucheventattheendofthe Cretaceousperiod(around70millionyearsago).Therewasanother,evenlarger,mass extinctionattheendofthePermianperiod(around250millionyearsago).ThePermian eventhasattractedmuchlessattentionthanothermassextinctionsbecausemostly unfamiliarspeciesperishedatthattime. ¡¡¡¡Thefossilrecordshowsatleastfivemassextinctionsinwhichmanyfamilies ofmarineorganismsdiedout.Theratesofextinctionhappeningtodayareasgreat astheratesduringthesemassextinctions.Manyscientistshavethereforeconcluded thatasixthgreatmassextinctioniscurrentlyinprogress. ¡¡¡¡Whatcouldcausesuchhighratesofextinction?Thereareseveralhypotheses, includingwarmingorcoolingofEarth,changesinseasonalfluctuationsorocean currents,andchangingpositionsofthecontinents.Biologicalhypothesesinclude ecologicalchangesbroughtaboutbytheevolutionofcooperationbetweeninsectsand floweringplantsorofbottom-feedingpredatorsintheoceans.Someoftheproposed mechanismsrequiredaverybriefperiodduringwhichallextinctionssuddenlytook place;othermechanismswouldbemorelikelytohavetakenplacemoregradually,over anextendedperiod,oratdifferenttimesondifferentcontinents.Somehypotheses failtoaccountforsimultaneousextinctionsonlandandintheseas.Eachmass extinctionmayhavehadadifferentcause.Evidencepointstohuntingbyhumansand habitatdestructionasthelikelycausesforthecurrentmassextinction. ¡¡¡¡AmericanpaleontologistsDavidRaupandJohnSepkoski,whohavestudiedextinction ratesinanumberoffossilgroups,suggestthatepisodesofincreasedextinction haverecurredperiodically,approximatelyevery26millionyearssincethemid- Cretaceousperiod.ThelateCretaceousextinctionofthedinosaursandammonoidswas justoneofthemoredrasticinawholeseriesofsuchrecurrentextinctionepisodes. Thepossibilitythatmas