英語(yǔ)必修三Unit 4 Astronomy課文翻譯

英語(yǔ)必修三Unit4Astronomy課文翻譯英語(yǔ)必修三Unit4Astronomy課文翻譯英語(yǔ)必修三Unit4Astronomy課文翻譯xxx公司英語(yǔ)必修三Unit4Astronomy課文翻譯文件編號(hào)：文件日期：修訂次數(shù)：第1.0次更改批準(zhǔn)審核制定方案設(shè)計(jì)，管理制度英語(yǔ)必修三Unit4Astronomy課文翻譯作者：未知來(lái)源：尚學(xué)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(méi)有人確切知道地球是怎么樣開(kāi)始形成的，因?yàn)樵诤茉绾茉谝郧暗厍蚓托纬闪?。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(zhì)投射到四面八方。然后，原子開(kāi)始形成并結(jié)合成恒星和其他天體。大爆炸后好幾十億年過(guò)去了，但地球還只是一團(tuán)塵埃。隨后它會(huì)變成什么沒(méi)人能知道，直到38-45億年前，這團(tuán)塵埃才慢慢地形成一個(gè)團(tuán)體的球狀物。地球開(kāi)始變得激烈動(dòng)蕩，不知道這個(gè)固體形狀是否會(huì)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?dú)?，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(lái)，地球的表面就開(kāi)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(lái)都消失了。水對(duì)于生命的發(fā)展會(huì)起關(guān)鍵作用，這一點(diǎn)在當(dāng)時(shí)并不明顯。很多科學(xué)家相信，由于地球上長(zhǎng)期有水存在，使得地球得以把有害氣體和酸性物質(zhì)溶解在海洋里。這就產(chǎn)生了一系列的反應(yīng)，使得生命就有可能開(kāi)始發(fā)展了。好幾百萬(wàn)年后，水的表面開(kāi)始出現(xiàn)了極小的植物。他們繁殖起來(lái)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(yú)類的發(fā)育進(jìn)一步創(chuàng)造了條件。接著，綠色植物開(kāi)始出現(xiàn)在陸地上。隨后，陸地上出現(xiàn)了動(dòng)物，其中有一些是昆蟲(chóng)，另外一些叫兩棲動(dòng)物，他們既能在陸地上生活，也能在海里生存。后來(lái)，當(dāng)植物長(zhǎng)大成了森林的時(shí)候，爬行動(dòng)物出現(xiàn)了。他們一般是通過(guò)孵蛋而繁衍后代的。再后來(lái)一些叫做恐龍的巨型動(dòng)物出現(xiàn)了。他們也生蛋，在地球上生存了一億四千多萬(wàn)年。然而，六千五百萬(wàn)年前，恐龍時(shí)代結(jié)束了。他們?yōu)槭裁磿?huì)突然滅絕至今仍是個(gè)謎?？铸埖臏缃^使地球上哺乳動(dòng)物的產(chǎn)生有了可能。這些動(dòng)物不同于以往所有的生物形式，因?yàn)樗麄兡軓捏w內(nèi)生產(chǎn)出幼崽并給幼崽哺乳。最后，大約260萬(wàn)年前，一些小巧聰明，長(zhǎng)著手腳的動(dòng)物出現(xiàn)了，他們散布在地球的各個(gè)地方。于是，他們接著成為這個(gè)行星上最重要的動(dòng)物。然而，他們對(duì)地球卻不怎么在意，他們把過(guò)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(lái)數(shù)百萬(wàn)年中，生命能否在地球上延續(xù)，取決于這個(gè)問(wèn)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(gè)月我有幸得到一個(gè)機(jī)會(huì)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(shuō),在我們的航行中會(huì)有三次引力的改變,而第一次的改變