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1、www.ylongedu.com新托福TPO8阅读原文(二):ExtinctionoftheDinosaursTPO-8-2：ExtinctionoftheDinosaurs Paleontologistshavearguedforalongtimethatthedemiseofthedinosaurswascausedbyclimaticalterationsassociatedwithslowchangesinthepositionsofcontinentsandseasresultingfromplatetecton
2、ics.OffandonthroughouttheCretaceous(thelastperiodoftheMesozoicera,duringwhichdinosaursflourished),largeshallowseascoveredextensiveareasofthecontinents.Datafromdiversesources,includinggeochemicalevidencepreservedinseafloorsediments,indicatethattheLateCretaceousclima
3、tewasmilderthantoday’s.Thedayswerenottoohot,northenightstoocold.Thesummerswerenottoowarm,northewinterstoofrigid.Theshallowseasonthecontinentsprobablybufferedthetemperatureofthenearbyair,keepingitrelativelyconstant. AttheendoftheCretaceous,thegeologicalrecordshowst
4、hattheseseawaysretreatedfromthecontinentsbackintothemajoroceanbasins.Nooneknowswhy.Overaperiodofabout100,000years,whiletheseaspulledback,climatesaroundtheworldbecamedramaticallymoreextreme:warmerdays,coolernights;hottersummers,colderwinters.Perhapsdinosaurscouldnot
5、toleratetheseextremetemperaturechangesandbecameextinct. Iftrue,though,whydidcold-bloodedanimalssuchassnakes,lizards,turtles,andcrocodilessurvivethefreezingwintersandtorridsummers?Theseanimalsareatthemercyoftheclimatetomaintainalivablebodytemperature.It’shardtounde
6、rstandwhytheywouldnotbeaffected,whereasdinosaurswerelefttoocrippledtocope,especiallyif,assomescientistsbelieve,dinosaurswerewarm-blooded.CriticsalsopointoutthattheshallowseawayshadretreatedfromandadvancedonthecontinentsnumeroustimesduringtheMesozoic,sowhydidthedino
7、saurssurvivetheclimaticchangesassociatedwiththeearlierfluctuationsbutnotwiththisone?Althoughwww.ylongedu.cominitiallyappealing,thehypothesisofasimpleclimaticchangerelatedtosealevelsisinsufficienttoexplainallthedata. Dissatisfactionwithconventionalexplanationsfordi
8、nosaurextinctionsledtoasurprisingobservationthat,inturn,hassuggestedanewhypothesis.Manyplantsandanimalsdisappearabruptlyfromthefossilrecordasonem
