资源描述：
《2014届最新高考英语一轮单元复习 精品阅读理解提升文章精选一百篇（88）.doc》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、2014届最新高考英语一轮单元复习精品阅读理解提升文章精选一百篇（88） Unit88IsThereLifeonMars? Formostofthe20thcentury,therehasbeenlifeonMars.Or,atleastinthemindsoftheEarthlings,whoinhabititsclosestplanetaryneighbor.Whenattheendofthe19thcentury,theAmericanastronomerPercivalLowellthoughthesawcanal
2、sontheRedPlanet,hewasconvincedthattheywerepartofaplanetwideirrigationsystem,builtbyanadvancedMartiancivilization. Then,in1965,theMariner4spacecraftflewpasttheRedPlanet.Itrevealedadesolateworld;theprospectsforlifewerefadingfast.Allhopediedin1976,whentheVikingLander
3、ofNasafailedtofindasingleorganicmolecule. TwentyyearsafterthelastmissiontoMarsfailedtodetectanysignsoflife,NasaispreparinganotherseriesofmissionstotheRedPlanettofindevidenceoflife.ThenewunmannedNasamissionstoMarsarearesultofthegrowingoptimismamongscientiststhatlif
4、eexists,ordidexist,onMars.ThestrongestevidenceinsupportoflifeonMarscomesfromthestudyofmicrobes.Scientistsarefindingmicrobesinmoreandmoreinhospitableconditions--inrockshundredsofmeterbelowtheEarth'ssurfaceandinvolcanicspringswellabovetheboilingpointofwater.Andthesec
5、onditionsareremarkablysimilartoconditionsonMars.Theseorganismscanliveandmultiplywithoutoxygenorlightinextremetemperatures,usingonlyrocksandwatertosustainthemselves. ScientistsbelievethatconditionsonMarsaround3.8billionyearsagoweresimilartothoseoftheearlyEarth,when
6、primitiveorganismswerespreadingthroughouroceans.Undertheseconditions,itishighlyprobablethatlifemayhavearisenonMarsaswell. EveniflifedidnotarisennaturallyonMars,itdoesnotmeanthatitcouldnothaveexistedthere.LifeformscouldhavebeentransferredbetweentheEarthandMarsindeb
7、riscreatedbytheimpactofcometsandasteroidsonthesurfaceofthetwoplanets.Eventoday,about500tonsofmaterialfromMarslandsonEartheveryyear.ItismainlyintheformofdustbutoccasionallyalargerchunkstrikestheEarth.Itisinthesechunksofrock,whichweremuchlargerandmorefrequentinthepas
8、t,thatlifeformscouldhavebeentransportedfromplanettoplanet.Buthowcouldtheselifeformshavesurvivedtheirjourneythroughspacefullofdeadlycosmicradiatio
