Unit 4 Astronomy Reading阅读课件-高中英语人教新课标必修三

Unit4AstronomyOnwhichplanetaretherelivesatpresent?earthHOWLIFEBEGANONTHEEARTHAtheoryabouttheoriginoftheuniverseTheformationoftheearthTheimportanceofwaterforlifeThedevelopmentofplantsandanimalsontheearth.ThearrivalofhumansandtheirinfluenceontheearthCheckyouranswers!Detailed-readingNooneknowsexactly

(how

theearthbegan),asithappenedsolongago.However,accordingtoawidelyaccepted

theory,theuniversebeganwitha“BigBang”(thatthrewmatterinalldirections).Afterthat,atomsbegantoformandcombinetocreatestarsandotherbodies.Forseveralbillionyearsafterthe“BigBang”,theearthwasstilljustacloudofdust.(What

itwastobecome)wasuncertainuntilbetween4.5and3.8billionyearsagowhenthedustsettledintoasolidglobe.Theearthbecamesoviolent

｛thatitwasnotclear(whether

theshapewouldlast

ornot)｝.Itexplodedloudlywithfireandrock.Theywereintimetoproducecarbondioxide,nitrogen,watervapourandothergases,(which

weretomaketheearth’satmosphere).(What

isevenmoreimportant)is(that

astheearthcooleddown,waterbegantoappearonitssurface).WaterhadalsoappearedonotherplanetslikeMarsbut,unliketheearth,ithaddisappearedlater.Itwasnotimmediatelyobvious(that

waterwastobefundamentaltothedevelopmentoflife).(What

manyscientistsbelieve)is(that

thecontinuedpresenceofwaterallowedtheearthtodissolve

harmfulgasesandacidsintotheoceansandseas).Thisproducedachainreaction,(which

madeitpossibleforlifetodevelop).Manymillionsofyearslater,thefirstextremelysmallplantsbegantoappearonthesurfaceofthewater.Theymultipliedandfilledtheoceansandseaswithoxygen,(which

encouragedthelaterdevelopmentofearlyshellfishandallsortsoffish).Next,greenplantsbegantogrowonland.Theywerefollowedintimebylandanimals.Somewereinsects.Others,called

amphibians,wereabletoliveonlandaswellasinthewater.Laterwhentheplantsgrewintoforests,reptilesappearedforthefirsttime.Theyproducedyounggenerallybylayingeggs.Afterthat,somehugeanimals,calleddinosaurs,developed.Theylaideggstooandexistedontheearthformorethan140millionyears.However,65millionyearsagotheageofthedinosaursended.(Why

theysuddenlydisappeared)stillremainsamystery.Thisdisappearancemadepossibletheriseofmammalsontheearth.Theseanimalsweredifferentfromalllifeformsinthepast,becausetheygavebirthtoyoungbabyanimalsandproducedmilktofeedthem.Finallyabout2.6millionyearsagosomesmallcleveranimals,nowwithhandsandfeet,appearedandspreadallovertheearth.Thustheyhave,intheirturn,becomethemostimportantanimalsontheplanet.Buttheyarenotlookingaftertheearthverywell.Theyareputtingtoomuchcarbondioxideintotheatmosphere,(which

preventsheatfromescapingfromtheearthintospace).Asaresultofthismanyscientistsbelievetheearthm