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1、HOWLIFEBEGANONTHEEARTH,地球上生命的起源,UNIT 4,课文讲解,1.Nooneknowsexactlyhowtheearthbegan,asithappenedsolongago.没有人确切知道地球是怎样开始形成的，因为在很早很早以前地球就形成了。2.However,accordingtoawidelyacceptedtheory,theuniversebeganwithaBigBangthatthrewmatterinalldirections.然而，一种普遍为人们所接受的理论是：宇宙起源于一次大爆炸，这次大爆炸将物质投射到四面八方。3.Afterthat,atoms
2、begantoformandcombinetocreatestarsandotherbodies.然后，原子开始形成并结合成恒星和其他天体。,Par 1,1.ForseveralbillionyearsaftertheBigBang,theearthwasstilljustacloudofdust.大爆炸后好几十亿年过去了，但地球还只是一团尘埃。2.Whatitwastobecomewasuncertainuntilbetween4.5and3.8billionyearsagowhenthedustsettledintoasolidglobe.随后它会变成什么没人能知道，直到3845亿年前，这
3、团尘埃才慢慢地形成一个固体的球状物。3.Theearthbecamesoviolentthatitwasnotclearwhethertheshapewouldlastornot.地球（开始）变得激烈动荡，不知道这个固体形状是否会继续存在下去。,Par 2,4.Itexplodedloudlywithfireandrock.Theywereintimetoproducecarbon,nitrogen,watervapourandothergases,whichweretomaketheearthsatmosphere.它（地球）猛烈地爆炸喷出了烈火与岩石，最终产生了碳，氮气，水蒸气和其他多种气
4、体，从而形成了地球的大气层。5.Whatisevenmoreimportantisthatastheearthcooleddown,waterbegantoappearonitssurface.更为重要的是，地球冷却了下来，地球的表面就开始出现了水。,1.WaterhadalsoappearedonotherplanetslikeMarsbut,unliketheearth,ithaddisappearedlater.在火星这些其他行星上都出现了水，但和地球不同的是，这些水后来都消失了。2.Itwasnotimmediatelyobviousthatwaterwastobefundamenta
5、ltothedevelopmentoflife.水对于生命的发展会起关键作用，这一点在当时并不明显。3.Whatmanyscientistsbelieveisthatthecontinuedpresenceofwaterallowedtheearthtodissolveharmfulgasesandacidsintotheoceansandseas.很多科学家相信，由于地球上长期有水存在，使得地球得以把有害气体和酸性物质溶解在海洋里。4.Thisproducedachainreaction,whichmadeitpossibleforlifetodevelop.这就产生了一系列的反应，使得生命
6、就有可能开始发展了。,Par 3,1.Manymillionsofyearslater,thefirstextremelysmallplantsbegantoappearonthesurfaceofthewater.好几百万年后，水的表面开始出现了极小的植物。2.Theymultipliedandfilledtheoceansandseaswithoxygen,whichencouragedthelaterdevelopmentofearlyshellfishandallsortsoffish.他们繁殖起来就使得海洋充满了氧气，这为早期的贝类及其他各种鱼类后来的进化创造了条件。3.Next,g
7、reenplantsbegantogrowonland.Theywerefollowedintimebylandanimals.接着，绿色植物开始出现在陆地上。4.Somewereinsects.Others,calledamphibians,wereabletoliveonlandaswellasinthewater.随后，陆地上出现了动物，其中有一些是昆虫，另外一些叫两栖动物，他们既能在陆上生活，也能在水里生存。,Par 4,5.Laterwhentheplantsgrewintoforests,reptilesappearedforthefirsttime.后来，当植物长成了森林的时候，
8、爬行动物首次出现了。6.Theyproducedyoungentirelybylayingeggs.他们一般是通过孵蛋而繁衍后代的。7.Afterthat,somehugeanimals,calleddinosaurs,developed.再后来一些叫做恐龙的巨型动物出现了。8.Theylaideggstooandexistedontheearthformorethan140millionyears.他们也生蛋，在地球上生存了一亿四千多万年。9.However,65millionyearsagotheageofthedinosaursended.然而，六千五百万年前，恐龙时代结束了。,10.W
9、hytheysuddenlydisappearedstillremainsamystery.他们为什么会突然灭绝至今仍是个谜。11.Thisdisappearancemadepossibletheriseofmammalsontheearth.恐龙的灭绝使地球上哺乳动物的增多有了可能。12.Theseanimalsweredifferentfromalllifeformsinthepast,becausetheygavebirthtoyoungbabyanimalsandproducedmilktofeedthem.这些动物不同于以往所有的生物形态，因为他们能从体内生产出幼仔并给幼仔哺乳。,1
10、.Finallyabout2.6millionyearsagosomesmallcleveranimals,nowwithhandsandfeet,appearedandspreadallovertheearth.最后，大约260万年前，一些小巧聪明，长着手脚的动物出现了，他们散布在地球的各个地方。2.Thustheyhave,intheirturn,becomethemostimportantanimalsontheplanet.于是，他们接着成为这个行星上最重要的动物。3.Buttheyarenotlookingaftertheearthverywell.然而，他们对地球却不怎么在意，,P
11、ar 5,4.Theyareputtingtoomuchcarbondioxideintotheatmosphere,whichpreventsheatfromescapingfromtheearthintospace.他们把过多的二氧化碳释放到大气层中，这使得地球上的热不能释放到太空中去。5.Asaresultofthis,manyscientistsbelievetheearthmaybecometoohottoliveon.因此，许多科学家相信地球可能会变得太热而不适合生物生存。6.Sowhetherlifewillcontinueontheearthformillionsofyears
12、tocomewilldependonwhetherthisproblemcanbesolved.所以，在未来的数百万年中，生命能否在地球上延续，取决于这个问题能否得到解决。,主语从句一个句子在复合句中充当主语叫主语从句。常用引导词：连接词：that(无词义)whetherThat he will come and help us is certain.Whether we stay or not makes no difference.连接代词:who(ever)whom what(ever)which(ever)whoseWho will go to the energy conferenc
13、e is not important.连接副词：when where how why When and where the test will be given is not decided.,1.引导主语从句的连词是不能省略的。That the earth is round is true2.That-从句作主语通常用it作先行词，而将that-从句置于句末，例如：It is true that the earth is round.结构：,Attention,a.It+be+形容词+that-从句It is necessary that 有必要It is important that重要的
14、是It is obvious that 很明显b.It+be+p.p.+that-从句It is believed that人们相信It is known to all that从所周知It has been decided that已决定,c.It+be+名词+that-从句It is common knowledge that 是常识It is a surprise that 令人惊奇的是It is a fact that 事实是d.It+不及物动词+that-分句It appears that似乎It happens that碰巧It occurred to me that 我突然想起,
15、2.表示“是否”意义时，一般用whether 而不用 if引导主语从句，Whether she will come or not is still a question3.有时可用形式主语it 代替主语从句：e.g.It is still a question whether she will come or not.It has not been decided yet when they will start.,4.无论主语从句有多长，一般做单数处理。e.g.When we will start has not been decided yet.注意：以what开始的主语从句如果后面的表语
16、是复数名词，系动词用复数形式。What he wants to buy are three books and two pens.,1.It is obvious to the students _ they should get well prepared for their future.A.as B.which C.whether D.that,2._ wants to stay in a hotel has to pay their own way.A.Anyone B.The one C.Whoever D.Who,练一练！,3.It is not immediately clear
17、 _ the financial crisis will soon be over.A.since B.what C.when D.whether,练一练！,_ leaves the room last ought to turn off the lights.A.Anyone B.The person C.Whoever D.Who _the sports meet will be held depends on the weather.A.Whenever B.If C.Whether D.That,_ is a fact that English is being accepted as
18、 an international language.A.There B.This C.That D.It,宾语从句一个句子在复合句中充当宾语就叫宾语从句连接词：that(无词义)whether ife.g.I dont know whether(if)you are willing to help me.连接代词：what(ever)who(ever)whose which(ever)等连接副词：when where how why等,特别提示1.由连接词that引导宾语从句时，that在句中不担任任何成分。Im glad that you have passed the exam.2.有些
19、词或词组如hate,love,enjoy,dislike,feel like,appreciate,take(认为),rely on,dont mind等，习惯上后面跟it做形式宾语，再接宾语从句。I take it that you will agree with us.,3.在接复合宾语的句子中，为了保持句子平衡，用it作形式宾语，而将从句放在句尾。常带复合宾语的动词有：make/find/see/hear/feel/think等。I think it necessary that I take plenty of water every day.4.某些动词后的宾语从句常用虚拟语气，如i
20、nsist，order，request，suggest等。I suggested that we(should)start before 5 o clock.,5.必须用whether 引导，不可用if:1).从句后有ornot时，不可用if:I dont know whether he will come or not.2).介词宾语通常用 whether 引导:It depends on whether he is coming or not.3).后接动词不定式时。Can you tell me whether to go or to stay?4).discuss 后面的宾语从句解释为
21、是否用whetherImagine you are in this situation,and discuss whether you should do something at once.,5)主语从句放在句首Whether we stay or not makes no difference.6）表语从句和同位语从句The question is whether we can get thereon time.7)当it做形式主语whether/if 都可引导主语从句It hasnt been decided whether/if we shall attend the meeting.
22、,6.用who，whom,which(ever),whose,when,what(ever),where,why,how,whoever等关联词引导的宾语从句相当于特殊疑问句，应注意句子语序要用陈述语序。Do you know how old he is?I want to know what he has told you.She always thinks of how she can work well.She will give whoever needs help a warm support.凡需要帮助的人，她都会给予热情的支持。,7.think,believe,imagine,s
23、uppose等动词引起的否定性宾语从句中，要把上述主句中的动词变为否定式。即将从句中的否定形式移到主句中。例如：We dont think you are here.我们认为你不在这。I dont believe he will do so.我相信他不会这样做。,如果主句主语为第一人称反意疑问句常与从句的主语和谓语保持一致；其他情况看主句。例如：I dont believe she has been to Australia,has she?我认为她没去澳大利亚，是吗？I dont believe that he can translate this book,?She thinks that
24、 her husband is the best one in the team,？,can he,doesnt she,I doubt if/whether he will pass the exam.I dont doubt that we will win the match.Do you doubt that he did it on his own?,doubt问题,肯定句中用 if/whether,否定句中用 that,疑定句中用 that,I doubt _he is telling the truth.We never doubt _ the plan will be carr
25、ied out.Does he doubt _ you are from Austria?Im doubtful _ he will agree to this.,if/whether,that,that,if/whether,宾语从句中的连接词that在以下三种情况下不能省略：（1）当that 从句与另一名词性从句并列作宾语时，第二个that不能省；（2）当that作介词宾语时，that不可省掉。（3）用it做形式宾语的宾语从句Everyone knew what happened and that she was worried.The reason lies in that she wo
26、rks harder than the others do.,宾语从句,He asked _ for a violin（MET1992）A.did I pay how much B.I paid how much C.how much did I pay D.how much I paid2It is generally considered unwise to give a child _he or she wants.(NMET1997)A.however B.whatever C.whichever D.whenever3.She is very dear to us.We have b
27、een prepared to do _ it takes to save her life.A.whichever B.however C.whatever D.whoever,4.The true value of life is not in _,but _.A.which we get;what give we B.what we get;what we give C.which do we get;what do we give D.how we get;that we give5.Have you seen Mary lately?My boss wants to know _.A.how she is getting along B.how is she getting along C.what she is getting along D.what is she getting along,6.I dont doubt _ hell come.A.thatB.ifC.whatD.whether7.Does anybody know _ we will have a sports meeting this weekend or not.A.if B.where C.whether D.that,
