Can humans live away from the Earth? 人类能远离地球生活吗？

　　Maybe it will be possible in the future but it is impossible now. 或许将来可以，但现在不行。

　　In our solar system, the Earth is probably the only planet where humans can live. 在我们的太阳系，地球是唯一适合人类居住的星球。

　　Some planets are too hot and some are too cold. 其他的星球要么太热，要么太冷。

　　But the Earth is warm, so humans can live on it. 但地球很温暖，所以人类才能在上面居住。

　　So what makes the Earth different from other planets? 什么使得地球不同于其他星球呢？

　　The Earth has ozone. 地球有臭氧。

　　Ozone is a thick layer of oxygen. It covers the Earth. 臭氧是一层厚厚的氧。它覆盖着地球。

　　What does it do? 它有什么作用？

　　It blocks much of the ultraviolet rays of the sun. 它阻挡了大部分来自太阳的紫外线。

　　Without ozone, the Earth will become too hot. 没有臭氧的话，地球将会变得非常热。