英語必修三Unit 4 Astronomy課文翻譯

英語必修三Unit4Astronomy課文翻譯英語必修三Unit4Astronomy課文翻譯英語必修三Unit4Astronomy課文翻譯xxx公司英語必修三Unit4Astronomy課文翻譯文件編號：文件日期：修訂次數(shù)：第1.0次更改批準審核制定方案設計，管理制度英語必修三Unit4Astronomy課文翻譯作者：未知來源：尚學苑2014-09-20LIFHOWEBEGANONTHEEARTHNooneknowsexactlyhowtheearthbegan,asithappenedsolongago.However,accordingtoawidelyacceptedtheory,theuniversebeganwitha"BigBang"thatthrewmatterinalldirections.Afterthat,atomsbegantoformandcombinetocreatestarsandotherbodies.Forseveralbillionyearsafterthe"BigBang",theearthwasstilljustacloudofdust.Whatitwastobecomewasuncertainuntilbetween4.5and3.8billionyearsagowhenthedustsettledintoasolidglobe.Theearthbecamesoviolentthatitwasnotclearwhethertheshapewouldlastornot.Itexplodedloudlywithfireandrock.Theywereintimetoproducecarbon,nitrogen,watervapourandothergases,whichweretomaketheearthsatmosphere.Whatisevenmoreimportantisthatastheearthcooleddown,waterbegantoappearonitssurface.WaterhadalsoappearedonotherplanetslikeMarsbut,unliketheearth,ithaddisappearedlater.Itwasnotimmediatelyobviousthatwaterwastobefundamentaltothedevelopmentoflife.Whatmanyscientistsbelieveisthatthecontinuedpresenceofwaterallowedtheearthtodissolveharmfulgasesandacidsintotheoceansandseas.Thisproducedachainreaction,whichmadeitpossibleforlifetodevelop.Manymillionsofyearslater,thefirstextremelysmallplantsbegantoappearonthesurfaceofthewater.Theymultipliedandfilledtheoceansandseaswithoxygen,whichencouragedthelaterdevelopmentofearlyshellfishandallsortsoffish.Next,greenplantsbegantogrowonland.Theywerefollowedintimebylandanimals.Somewereinsects.Others,calledamphibians,wereabletoliveonlandaswellasinthewater.Laterwhentheplantsgrewintoforests,reptilesappearedforthefirsttime.Theyproducedyoungenerallybylayingeggs.Afterthat,somehugeanimals,calleddinosaurs,developed.Theylaideggstooandexistedontheearthformorethan140millionyears.However,65millionyearsagotheageofthedinosaursended.Whytheysuddenlydisappearedstillremainsamystery.Thisdisappearancemadepossibletheriseofmammalsontheearth.Theseanimalsweredifferentfromalllifeformsinthepast,becausetheygavebirthtoyoungbabyanimalsandproducedmilktofeedthem.Finallyabout2.6millionyearsagosomesmallcleveranimals,nowwithhandsandfeet,appearedandspreadallovertheearth.Thustheyhave,intheirturn,becomethemostimportantanimalsontheplanet.Buttheyarenotlookingaftertheearthverywell.Theyareputtingtoomuchcarbondioxideintotheatmosphere,whichpreventsheatfromescapingfromtheearthintospace.Asaresultofthis,manyscientistsbelievetheearthmaybecometoohottoliveon.Sowhetherlifewillcontinueontheearthformillionsofyearstocomewilldependonwhetherthisproblemcanbesolved.地球上生命的起源沒有人確切知道地球是怎么樣開始形成的，因為在很早很在以前地球就形成了。然而，一種普遍為人們所接受的理論是：宇宙起源于一次大爆炸，這次大爆炸將物質投射到四面八方。然后，原子開始形成并結合成恒星和其他天體。大爆炸后好幾十億年過去了，但地球還只是一團塵埃。隨后它會變成什么沒人能知道，直到38-45億年前，這團塵埃才慢慢地形成一個團體的球狀物。地球開始變得激烈動蕩，不知道這個固體形狀是否會繼續(xù)存下去。它猛烈地爆炸噴出了烈火與巖石，最終產(chǎn)生了碳，氮氣，水蒸氣和其他多種氣體，從而形成了地球的大氣層。更為重要的是，地球冷卻了下來，地球的表面就開始出現(xiàn)了水。在火星這些其他行星上都出現(xiàn)了水，但和地球不同的是，這些水后來都消失了。水對于生命的發(fā)展會起關鍵作用，這一點在當時并不明顯。很多科學家相信，由于地球上長期有水存在，使得地球得以把有害氣體和酸性物質溶解在海洋里。這就產(chǎn)生了一系列的反應，使得生命就有可能開始發(fā)展了。好幾百萬年后，水的表面開始出現(xiàn)了極小的植物。他們繁殖起來就使得早期的海洋充滿了氧氣，這為早期的貝類及其他各種魚類的發(fā)育進一步創(chuàng)造了條件。接著，綠色植物開始出現(xiàn)在陸地上。隨后，陸地上出現(xiàn)了動物，其中有一些是昆蟲，另外一些叫兩棲動物，他們既能在陸地上生活，也能在海里生存。后來，當植物長大成了森林的時候，爬行動物出現(xiàn)了。他們一般是通過孵蛋而繁衍后代的。再后來一些叫做恐龍的巨型動物出現(xiàn)了。他們也生蛋，在地球上生存了一億四千多萬年。然而，六千五百萬年前，恐龍時代結束了。他們?yōu)槭裁磿蝗粶缃^至今仍是個謎?？铸埖臏缃^使地球上哺乳動物的產(chǎn)生有了可能。這些動物不同于以往所有的生物形式，因為他們能從體內生產(chǎn)出幼崽并給幼崽哺乳。最后，大約260萬年前，一些小巧聰明，長著手腳的動物出現(xiàn)了，他們散布在地球的各個地方。于是，他們接著成為這個行星上最重要的動物。然而，他們對地球卻不怎么在意，他們把過多的二氧化氮釋放到大氣層中，這使得地球上的熱不能釋放到太空中去。地球可能因此變得太熱而不適合生物生存。所以，在未來數(shù)百萬年中，生命能否在地球上延續(xù)，取決于這個問題能否得到解決。AVISITTOTHEMOONLastmonthIwasluckyenoughtohaveachancetomakeatripintospacewithmyfriendLiYanping,anastronomer.Wevisitedthemooninourspaceship!Beforeweleft,LiYanpingexplainedtomethattheforceofgravitywouldchangethreetimesonourjourneyandthatthefirstchangewouldbethemostpowerful.Thenwewereoff.Astherocketroseintotheair,wewerepushedbackintoourseatsbecauseweweretryingtoescapethepulloftheearthsgravity.Itwassohardthatwecouldnotsayanythingtoeachother.GraduallytheweightlessenedandIwasabletotalktohim."Whyisthespaceshipnotfallingbacktotheearth

OntheearthifIfallfromatreeIwillfalltotheground."Iasked."Wearetoofarfromtheearthnowtofeelitspull,"heexplained,"sowefeelasifthereisnogravityatall.Whenwegetclosertothemoon,weshallfeelitsgravitypullingus,butitwillnotbeasstrongapullastheearths."Icheeredupimmediatelyandfloatedweightlesslyaroundinourspaceshipcabinwatchingtheearthbecomesmallerandthemoonlarger.

Whenwegotthere,Iwantedtoexploreimmediately."Comeon,"Isaid."Ifyouareright,mymasswillbelessthanontheearthbecausethemoonissmallerandIwillbeabletomovemorefreely.ImightevengrowtallerifIstayherelongenough.Ishallcertainlyweighless!"Ilaughedandclimbeddownthestepsfromthespaceship.ButwhenItriedtostepforward,IfoundIwascarriedtwiceasfarasontheearthandfellover."Ohdear,"Icried,"walkingdoesneedabitofpracticenowthatgravityhaschanged."AfterawhileIgotthehangofitandwebegantoenjoyourselves.Leavingthemoonsgravitywasnotaspainfulasleavingtheearths.Butreturningtotheearthwasveryfrightening.Wewatched,amazedasfirebrokeoutontheoutsideofthespaceshipastheearthsgravityincreased.Againwewerepushedhardintoourseatsaswecamebacktoland."Thatwasveryexhaustingbutveryexcitingtoo,"Isaid."NowIknowmuchmoreaboutgravity!Doyouthinkwecouldvisitsomestarsnexttime""Ofcourse,"hesmiled,"whichstarwouldyouliketogoto"月球之旅我的朋友李彥平是一位宇航員。上個月我有幸得到一個機會同他一起去太空旅行。我們乘宇宙飛船參觀了月球。在啟程以前,李彥平向我解釋說,在我們的航行中會有三次引力的改變,而第一次的改變