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What is Inside the Earth?


The Earth has layers


The size of the Earth -- about 12,750 kilometers (km) in diameter -- was known by the ancient Greeks, but it was not until the turn of the 20th century that scientists determined that our planet is made up of three main layers: crust, mantle, and core. This layered structure can be compared to that of a boiled egg. The crust, the outermost layer, is rigid and very thin compared with the other two. Beneath the oceans, the crust varies little in thickness, generally extending only to about 5 km. The thickness of the crust beneath continents is much more variable but averages about 30 km; under large mountain ranges, such as the Alps or the Sierra Nevada, however, the base of the crust can be as deep as 100 km. Like the shell of an egg, the Earth's crust is brittle and can break. This image shows cutaway views showing the internal structure of the Earth. In the lower left, this view drawn to scale demonstrates that the Earth's crust literally is only skin deep. On the right, the view expands the top layers (not drawn to scale) to show the Earth's three main layers (crust, mantle, and core) in more detail.


Diagram courtes USGS

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