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HOW LIFE BEGAN ON THE EARTH

地球上生命的起源

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 \Bang\that threw matter in all directions.After that, atoms began to form and combine to create stars and other bodies.

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。

For several billion years after the \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 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.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。

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.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。

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.

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。

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.

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

月球之旅

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!我的朋友李彦平是一位宇航员。上个月我有幸得到一个机会同他一起去太空旅行。我们乘宇宙飞船参观了月球。

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. \is the spaceship not falling back to the earth? On the earth if I fall from a tree I will fall to the ground.\far from the earth now to feel its pull,\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.

在启程以前,李彦平向我解释说,在我们的航行中会有三次引力的改变,而第一次的改变将是最强的。随后我们就启航了。随着火箭徐徐升空,我们慢慢逃离地球的引力。但这种引力太强了,把我们重重地向 后推在座位上,以至于我们彼此间都不能说话了。随后,这个力量

匮慢减小,我才能够同他讲话。我问道: \为什么太空船不会向后朝地球的方向落下去呢?在地球上的时候,如果我从树上掉下来,总会朝地上落下去的。\李彦平解释说\现在我们离地球太远了,感觉不到地球的拉力,所以我们好像一点儿也感觉不到地球引力了。当我们更接近月球时,就会感到月球的引力在拉我们。但是,月球的引力不像地球的引力 那么大。\我立刻感到很高兴,由于失重我在太空舱里飘来飘去,我望着(身后的)地球越来越小,而(前 方的)月球越来越大。

When we got there, I wanted to explore immediately. \mass 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!\and climbed down the steps from the spaceship. But when I tried to step forward, I found I was carried twice as far as on the earth and fell over. \practice now that gravity has changed.\ourselves.我们到达月球时,我就想立即进行探测。\来吧,\我说,\要是你讲得对,我的重量就会比在地球上小,因为月亮比地球小,而我就能更自由地活动了。如果我在月球上呆的时间足够长的话,我甚至可能长得更高,我的体重肯定也会变得更轻! \我笑着从火箭的梯级上爬下来。而当我试着向前迈步的时候,我发觉我被送出去很远,步子的跨度竟是在地球上的两倍,因而我摔倒了。\天哪,\我大声说,\重力改变了,看来走路也的确需要练一练了。\过了一会儿,我才掌握了走路的诀窍,这才开始感到自如了。

Leaving the moons gravity was not as painful as leaving the earths. But returning to the earth was very frightening. We watched, amazed as fire broke out on the outside of the spaceship as the earths gravity increased. Again we were pushed hard into our seats as we came back to land. \was very exhausting but very exciting too,\you think we could visit some stars next time?\like to go to?\摆脱月球引力不像摆脱地球引力那样痛苦。但是返回到地球的经历却是非常吓人的。我们惊奇地看着,随着地球引力的增加,宇宙飞船的外层燃烧起火。当我们回到地面时,我们又感到被重重地推倒在座位上。我说道\真是精疲力竭了,但也很激动人心。关于引力,我现在就懂得更多了。你认为下次我们可以上星球上去参观吗? \\当然可以,\他笑着说,\你想到哪颗星球上去呢? \