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Structure of the Earth

The interior of the Earth, like that of the other terrestrial planets, is chemically divided into layers.

The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.

Many of the rocks now making up the Earth's crust formed less than 100 million years ago; however the oldest known mineral grains are 4.4 billion years old, indicating that the Earth has had a solid crust for at least that long.

Note:   The above text is excerpted from the Wikipedia article "Structure of the Earth", which has been released under the GNU Free Documentation License.
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