英语必修三Unit 4 Astronomy课文翻译 作者：未知 来源：尚学苑 2014-09-20 LIF HOW E 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 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 and 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 vapour and other gases, which were to make the earths 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 enerally 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 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. 地球上生命的起源 没有人确切知道地球是怎么样开始形成的，因为在很早很在以前地球就形成了。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。然后，原子开始形成并结合成恒星和其他天体。 大爆炸后好几十亿年过去了，但地球还只是一团尘埃。随后它会变成什么没人能知道, 直到38-45亿年前，这团尘埃才慢慢地形成一个团体的球状物。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下去。它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体，从而形成了地球的大气层。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。 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。水对于 生命的发展会起关键作用，这一点在当时并不明显。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。这就产生了一系列的反应，使得 生命就有可能开始发展了。 好几百万年后，水的表面开始出现了极小的植物。他们繁殖起来就使得早期的海洋充满 了氧气，这为早期的贝类及其他各种鱼类的发育进一步创造了条件。接着，绿色植物开始出 现在陆地上。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 能在陆地上生活，也能在海里生存。后来，当植物长大成了森林的时候，爬行动物出现了。 他们一般是通过孵蛋而繁衍后代的。再后来一些叫做恐龙的巨型动物出现了。他们也生蛋, 在地球上生存了一亿四千多万年。然而，六千五百万年前，恐龙时代结束了。他们为什么会 突然灭绝至今仍是个谜。恐龙的灭绝使地球上哺乳动物的产生有了可能。这些动物不同于以 往所有的生物形式，因为他们能从体内生产出幼崽并给幼崽哺乳。 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。于是，他们接着成为这个行星上最重要的动物。然而，他们对地球却不怎么在意, 他们把过多的二氧化氮释放到大气层中，这使得地球上的热不能释放到太空中去。地球可能 因此变得太热而不适合生物生存。所以，在未来数百万年中，生命能否在地球上延续，取决 于这个问题能否得到解决。 A VISIT TO THE MOON Last month I was lucky enough to have a chance to make a trip into space with my friend Li Yanping, an astronomer. We visited the moon in our spaceship! Before we left, Li Yanping explained to me that the force of gravity would change three times on our journey and that the first change would be the most powerful. Then we were off. As the rocket rose into the air, we were pushed back into our seats because we were trying to escape the pull of the earths gravity. It was so hard that we could not say anything to each other. Gradually the weight lessened and I was able to talk to him. "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," he explained, "so we feel as if there is no gravity at all. When we get closer to the moon, we shall feel its gravity pulling us, but it will not be as strong a pull as the earths." I cheered up immediately and floated weightlessly around in our spaceship cabin watching the earth become smaller and the moon larger. When we got there, I wanted to explore immediately. "Come o