The atmosphere is as much a part of the earth as -------- it

让我们这样分析：
1.The atmosphere is a part of the earth
2.its soil and water of its lakes,rivers and oceans ARE (also) part of the earth.
3.one is as much a part of the earth as the other.
放在一起就是
The atmosphere is as much a part of the earth as ARE its soil and water of its lakes,rivers and oceans
它们都是地球的一部分