ROBERT BROCKSMITH / SCIENCE PHOTO LIBRARY ROBERT BROCKSMITH / SCIENCE PHOTO LIBRARY
Earth's centre, computer artwork. The Earth has an equatorial diameter of 12,756 kilometres. The orange centre here could represent the mantle, a layer between the outer core (not seen) and the surface crust (transparent). The mantle is a highly viscous liquid composed of silicate rocks, on which the solid plates of the crust float.
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