帮我看看、检查检查些列句子有没有语法错误（英语）

这短文有几个语法错误.我逐句为你改如下：

The moon is the most thoroughly studied celestial.
改为
The moon is the most thoroughly studied celestial body.
The moon's age is about 4600000000 years.
改为
The moon's age is about 4.6 billion years.

The moon and the earth as a shell, mantle, core layerstructure.
改为
The moon, like the earth, has a layered structure consisting of a shell, a mantle, and a core.

The outer shell of the month average thickness of about 60-65 km.
改为
The outer shell of the moon has an average thickness of about 60-65 km.

Lunar crust below to 1000 km depth is the lunar mantle, it accounts for most of the volume of the moon.
改为
Below the lunar crust, to 1000 km. depth, is the lunar mantle, which accounts for most of the volume of the moon.

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我是加拿大人,前海外英语老师.