Overview of Earth地球的概述
Earth is where we all live. 地球是我们所有人生活的地方。
It is our home in the solar system. 它是我们在太阳系的家。
There is no other place for us to live. 我们没有别的地方可住。
Earth isn’t just any planet. 地球不是普通的行星。
It’s a very special place. 这是一个非常特别的地方。
It’s special because we depend on it for many things. 它很特别，因为我们在很多事情上都依赖它。
Because of its importance we need to take care of it.因为它的重要性，我们需要照顾它。
We depend on the earth for its air, its water and many of its natural resources. 我们依赖地球的空气、水和许多自然资源。
Natural resources, such as coal and oil, give us energy. 煤和石油等自然资源为我们提供能源。
Other natural resources we depend on include forests and soil. 我们所依赖的其他自然资源包括森林和土壤。
Forests provide clean air and wood for building houses. 森林提供清洁的空气和建造房屋的木材。
Soil is needed to grow plants and keep them healthy. 土壤是植物生长和保持健康所必需的。
We need to take care of these resources and not waste them.我们需要爱护这些资源，不要浪费它们。
The earth is a large,rotating sphere, about 4.5 billion years old. 地球是一个巨大的旋转球体，大约有45亿年的历史。
Theequatorwhich divides the earth into twohemispheres, is about 40,000 kilometers long. 赤道把地球分成两个半球，大约有4万公里长。
The Earth'sdiameteris 12,756 kilometers. 地球的直径是12756公里。
Itsradiusis half that, or 6,378 kilometers. 它的半径是这个的一半，即6378千米。
The radius is the distance from the Earth’s center to its surface. 半径是地球中心到地表的距离。
Most of the Earth’s surface is covered by water. 地球表面大部分被水覆盖。
The rest of the Earth’s surface is land.地球表面的其余部分是陆地。
Just above the Earth's surface is the atmosphere. 大气层就在地球表面的正上方。
The atmosphere is a layer of gases, about 500 kilometers thick. 大气层是一层大约500公里厚的气体。
These gases included oxygen, nitrogen and carbon dioxide. 这些气体包括氧气、氮气和二氧化碳。
This mixture of gases is the air that we breathe. 这种混合气体就是我们呼吸的空气。
As we move about the Earth’s surface, the air gets thinner. 当我们在地球表面移动时，空气变得越来越稀薄。
At high altitudes, the air is too thin to breathe. 在高海拔地区，空气稀薄得无法呼吸。
At the edge of the atmosphere is space. 大气层的边缘是太空。
There is no air at all in space.太空中根本没有空气。