英语翻译How life began on the earthNo one knows exactly how the

英语翻译
How life began on the earth
No one knows exactly how the earth began,as it happened so long ago.However,according to a widely accepted theory,the universe began with a “Big Bang” that threw matter in all directions.After that,atoms began to form and combine to create stars and other bodies.
For several billion years after the “Big Bang”,the earth was still just a cloud of dust.What it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust settled into a solid globe.The earth became so violent that it was not clear whether the shape would last or not.It exploded loudly with fire and rock.They were in time to produce carbon,nitrogen,water vapor and other gases,which were to make the earth’s atmosphere.What is even more important is that as the earth cooled down,water began to appear on its surface.
Water had also appeared on other planets like Mars but unlike the earth,it had disappeared later.It was not immediately obvious that water was to be fundamental to the development of life.What many scientists believe is that the continued presence of water allowed the earth to dissolve harmful gases and acids into the oceans and seas.This produced a chain reaction,which made it possible for life to develop.
Many millions of years later,the first extremely small plants began to appear on the surface of the water.They multiplied and filled the oceans and seas with oxygen,which encouraged the later development of early shellfish and all sorts of fish.Next,green plants began to grow on land.They were followed in time by land animals.Some were insects.Others,called amphibians,were able to live on land as well as in the water.Later when the plants grew into forests,reptiles appeared for the first time.They produced young generally by laying eggs.After that,some huge animals,called dinosaurs,developed.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 ended.Why they suddenly disappeared still remains a mystery.This disappearance made possible the rise of mammals on the earth.These animals were different from all life forms in the past,because they gave birth to young baby animals and produced milk to feed them.
Finally about 2.6 million years ago some small clever animals,now with hands and feet,appeared and spread all over the earth.Thus they have,in their turn,become the most important animals on the planet.But they are not looking after the earth very well.They are putting too much carbon dioxide into the atmosphere,which prevents heat from escaping from the earth into space.As a result of this,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 will depend on whether this problem can be solved.

地球上的生命是如何开始的?
没人确切知道地球何时开始,因为这起始于很久很久以前.然而,更具普遍接受的一个理论,宇宙其实于宇宙大爆炸,大爆炸中所有的物质被射向了各个角落.自从那时候开始,原子开始形成,并合并创造出星球和其他物体.
在宇宙大爆炸的数百万年后,地球只是一团尘埃.它真正形成大约是在45亿至38亿年前,那时尘埃逐渐聚拢成为一个固体星球.但是这时的地球很不稳定,不知它的形状是否还会维持.地球上发生爆炸,迸发出火焰和岩石.它们立即产生碳、氮气、水蒸气和其他气体,这就是将来形成大气层的主要元素.更重要的是,当地球的温度逐渐下降时,水蒸气开始冷凝附着在地球的表面.
水同样也出现在其他的星球上,比如说火星.但与地球不同,它在后来便消失了.水是不是生命的产生的基础,这点仍然不是很清晰.很多科学家认为,水的持续产生使得地球上的有害气体和酸性物质进入海洋.这引起了一系列的反应,这些反应同样保证了生命的产生.
几百万年后,第一株极小的植物产生在了水的表面.它们使得海洋之中富有氧气,这对今后贝类、鱼类的演化产生了积极的作用.其后,绿色的植物开始在地面上生长.此后陆地上的动物也出现了.有些是昆虫.其它的是两栖动物,它们可以在陆地和水中生存.当植物长成了森林之后,爬行动物出现了.它们通过生蛋繁衍后代.以后恐龙出现了,它们同样通过生蛋繁殖并在地球上存活了1亿4千万年以上.然而6千5百万年前恐龙时代终结.究竟恐龙为何会突然消失仍然是个迷.恐龙的消失使得哺乳动物在地球上出现.这些动物与之前的不同,因为它们直接生出后代动物并用母乳喂养它们.
最后在260万年前出现了一些小型的智能动物,现在有手和脚,并在地球上各处出现并行遍地球.它们因此一跃成为了地球上最重要的动物.但是它们漠不关心地球.它们将二氧化碳排向大气中,使得热无法从地球上有效的散失.因此,许多科学家认为地球会变得过热而无法生存.因而接下来的数百万年中是否仍然有生命存在于这个星球仍就尚未解决.