人教版英语必修3课文讲解Unit4.ppt

英语必修英语必修3 Unit 4 3 Unit 4 词汇拓展词汇拓展1.astronomy n.天文学天文学 astronomer n.天文学家天文学家2.theory n.理论理论 practice n.实践实践3.globe n.球体球体 global adj.全球的全球的4.violent adj.剧烈的剧烈的 violently adv.剧烈地剧烈地 violence n.暴力暴力英语必修英语必修3 Unit 4 3 Unit 4 词汇拓展词汇拓展5.like prep.像像一样一样 unlike prep.与与不同不同6.presence n.在场在场 present adj.在场的在场的7.harm n.有害有害 harmful adj.有害的有害的8.react v.反应反应 reaction n.反应反应英语必修英语必修3 Unit 4 3 Unit 4 词汇拓展词汇拓展9.exist v.存在存在 existence n.存在存在10.preventfrom 阻止阻止做做.stopfrom 阻止阻止做做.11.puzzle v.使困惑使困惑 puzzled adj.困惑的困惑的 puzzling adj.令人困惑的令人困惑的12.biology n.生物生物 biologist n.生物学家生物学家英语必修英语必修3 Unit 4 3 Unit 4 词汇拓展词汇拓展13.physics n.物理物理 physicist n.物理学家物理学家14.lessen v.减少减少 decrease v.减少减少15.weight n.重量重量 weightless adj.失重的失重的 weightlessly adv.失重地失重地16.exhaust vt.使疲惫使疲惫 exhausted adj.疲惫的疲惫的 exhausting adj.令人疲惫的令人疲惫的 英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解HOW LIFE BEGAN ON THE EARTH地球上生命的起源地球上生命的起源No one knows exactly how the earth began开开始形成的始形成的,as因为因为 it happened 形成形成so long ago.However,according to根据根据 a widely accepted人们普遍接受的人们普遍接受的 theory,the universe began with a“Big Bang”大爆炸大爆炸 that threw投投射射 matter物质物质 in all directions四面八方四面八方.After that,atoms began to form and combine to create stars恒星恒星 and other bodies天体天体.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解 For several billion years几十亿年几十亿年 after the“Big Bang”,the earth was still just a cloud of dust一团尘埃一团尘埃.What it was to become随后会变成什么随后会变成什么 was uncertain没有没有人知道人知道 until between 4.5 and 3.8 billion38-45亿亿 years ago when the dust settled into a solid globe形成一个固体的球状物形成一个固体的球状物.The earth became so violent激烈动荡激烈动荡 that it was not clear不知道不知道 whether the shape固固体形状体形状 would last存在存在 or not.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解 It地球地球 exploded loudly剧烈爆剧烈爆炸炸 with fire and rock.They were in time最终最终 to produce carbon dioxide碳碳,nitrogen氮气氮气,water vapor水蒸气水蒸气 and other gases,which were to make the earths atmosphere大气层大气层.What is even more important is that as the earth cooled down冷却冷却,water began to appear on its surface.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解 Water had also appeared on other planets行星行星 like Mars火星火星 but,unlike the earth,it had disappeared later.It was not immediately当时当时 obvious that water was to be fundamental起关键作用起关键作用 to the development of life.What many scientists believe is that the continued presence持续持续存在存在 of water allowed the earth to dissolve溶解溶解 harmful gases and acids酸性物质酸性物质 into the oceans and seas.This produced a chain reaction一系列的反应一系列的反应,which made it possible for life to develop开始发展开始发展.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解 Many millions of years好几百万年好几百万年 later,the first extremely small plants极小的植物极小的植物 began to appear on the surface of the water.They multiplied繁殖繁殖 and filled the oceans and seas with oxygen氧气氧气,which encouraged创造创造条件条件 the later development 进化进化of early shellfish贝类贝类 and all sorts of fish.Next,green plants began to grow on land.They were followed in time随后随后 by land animals.Some were insects.Others,called amphibians两栖动两栖动物物,were able to live on land as well as也也 in the water.Later when the plants grew into forests,reptiles爬行动物爬行动物 appeared for the first time.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解 They produced young繁衍后代繁衍后代 generally by laying eggs孵卵孵卵.After that,some huge animals,called dinosaurs,developed出现出现.They laid eggs too and existed on the earth for more than 140 million years.However,65 million years ago the age of the dinosaurs恐龙恐龙时代时代 ended.Why they suddenly disappeared still remains a mystery仍然是个迷仍然是个迷.This disappearance 恐龙的灭绝恐龙的灭绝made possible the rise of mammals哺乳动物哺乳动物 on the earth.These animals were different from all life forms生命生命形式形式 in the past,because they gave birth to young baby animals产出幼子产出幼子and produced milk to feed them哺乳哺乳.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解 Finally about 2.6 million years ago some small clever animals,now with hands and feet,appeared and spread散布在散布在 all over the earth.Thus they have,in their turn接着接着,become the most important animals on the planet.But they are not looking after对对不怎么在意不怎么在意 the earth very well.They are putting 释放释放too much carbon dioxide into the atmosphere,which prevents使使不能散发到不能散发到 heat from escaping from the earth into space.As a result of this因此因此,many scientists believe the earth may become too hot to live on.So whether life will continue on the earth for millions of years to come未来数百万年未来数百万年 will depend on取决于取决于 whether this problem can be solved.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解A VISIT TO THE MOON P30 Last month I was lucky enough to have a chance to make a trip into space太空旅游太空旅游 with my friend Li Yanping,an astronomer.We visited the moon in our spaceship!英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解 Before we left,Li Yanping explained to me that the force of gravity重力重力 would change three times on our journey and that the first change would be the most powerful最强最强.Then we were off启航启航.As the rocket rose into the air升入空中升入空中,we were pushed back into our seats because we were trying to escape the pull of the earths gravity摆脱地球引力摆脱地球引力.It was so hard强强 that we could not say anything to each other.Gradually the weight lessened力量减小力量减小 and I was able to talk to him.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解“Why is the spaceship not falling back to the earth?On the earth if I fall from a tree I will fall to the ground.”I asked.“We are too far from the earth now to feel its pull引力引力,”he explained,“so we feel as if no gravity引力引力 at all.When we get closer to the moon,we shall feel its gravity pulling牵引牵引 us,but it will not be as strong a pull as the earths.”I cheered up欢呼欢呼 immediately and floated weightlessly失失重漂浮重漂浮 around in our spaceship cabin太太空舱空舱 watching the earth become smaller and the moon larger.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解When we got there到达月球到达月球,I wanted to explore 探探测测immediately.“Come on来吧来吧,”I said.“If you are right,my weight will be less than on the earth because the moon is smaller and I will be able to move more freely.I might even grow taller if I stay here long enough.I shall certainly weigh less体重减体重减轻轻!”I laughed and climbed down爬下来爬下来 the steps台台阶阶 from the spaceship.But when I tried to step forward向前迈步向前迈步.I found I was carried被送出很远被送出很远 twice as far as on the earth步子竟是地球上的两倍远步子竟是地球上的两倍远 and fell over摔倒摔倒.“Oh dear天哪天哪,”I cried大声说大声说,“walking does need a bit of practice now that gravity has changed.”After a while I got the hang of it掌握了掌握了走路的诀窍走路的诀窍 and we began to enjoy ourselves感觉自感觉自如如.英语必修英语必修3 Unit 43 Unit 4课文讲解课文讲解Leaving 摆脱摆脱the moons gravity was not as painful痛苦痛苦 as leaving the earths.But returning to the earth was very frightening非非常吓人常吓人.We watched,amazed 惊奇地惊奇地as fire broke out燃烧起火燃烧起火 on the outside of the spaceship as the earths gravity increased.Again we were pushed hard重重地推倒重重地推倒 into our seats as we came back to land.“That was very exhausting筋疲力尽筋疲力尽 but very exciting too,”I said.“Now I know much more about gravity!Do you think we could visit some stars星球星球 next time?”“Of course,”he smiled,“which star星球星球 would you like to go to?”