The internal of the earth is segmented into core, mantle and crust.

During the formation of the earth, a large part of the constituents became molten. This resulted in the unmixing of materials of different density and in the segmentation of earth. The core mainly consists of dense iron and nickel, the crust, in contrast, of less dense silicates. This segmentation can be examined by measuring the velocity of seismic waves across the earth. The figure (not true to scale) shows the core as a red and a yellow layer, the mantle as the layer above with the red colour gradient, and the crust as the external, dark layer.