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1、英语必修三Unit4Astronomy课文翻译作者：未知来源：尚学苑2014-09-20LIFHOWEBEGANONTHEEARTHNooneknowsexactlyhowtheearthbegan,asithappenedsolongago.However,accordingtoawidelyacceptedtheory,theuniversebeganwitha"BigBang"thatthrewmatterinalldirections.Afterthat,atomsbegantoformandcombinetocreatestarsandotherbo
2、dies.ForseveralbillionyearsaftertheuBigBang”，theearthwasstilljustacloudofdust.Whatitwastobecomewasuncertainuntilbetween4.5and3.8billionyearsagowhenthedustsettledintoasolidglobe・Theearthbecamesoviolentthatitwasnotclearwhethertheshapewouldlastornot.Itexplodedloudlywithfireandrock.They
3、wereintimetoproducecarbon,nitrogen,watervapourandothergases,whichweretomaketheearthsatmosphere.Whatisevenmoreimportantisthatastheearthcooleddown,waterbegantoappearonitssurface・WaterhadalsoappearedonotherplanetslikeMarsbut,unliketheearth,ithaddisappearedlater.Itwasnotimmediatelyobvio
4、usthatwaterwastobefundamentaltothedevelopmentoflife.Whatmanyscientistsbelieveisthatthecontinuedpresenceofwaterallowedtheearthtodissolveharmfulgasesandacidsintotheoceansandseas・Thisproducedachainreaction,whichmadeitpossibleforlifetodevelop.Manymillionsofyearslater,thefirstextremelysm
5、allplantsbegantoappearonthesurfaceofthewater.Theymultipliedandfilledtheoceansandseaswithoxygen,whichencouragedthelaterdevelopmentofearlyshellfishandallsortsoffish.Next,greenplantsbegantogrowonland.Theywerefollowedintimebylandanimals・Somewereinsects・Others，calledamphibians,wereableto
6、liveonlandaswellasinthewater.Laterwhentheplantsgrewintoforests,reptilesappearedforthefirsttime.Theyproducedyoungenerallybylayingeggs.Afterthat,somehugeanimals,calleddinosaurs,developed・Theylaideggstooandexistedontheearthformorethan140millionyears・However,65millionyearsagotheageofthe
7、dinosaursended.Whytheysuddenlydisappearedstillremainsamystery.Thisdisappearancemadepossibletheriseofmammalsontheearth・Theseanimalsweredifferentfromalllifeformsinthepast,becausetheygavebirthtoyoungbabyanimalsandproducedmilktofeedthem.Finallyabout2.6millionyearsagosomesmallcleveranima
8、ls,nowwithhandsandf
