Mantle

The middle layer of a planet, such as Earth, lying around the outside of the core and under the crust. It is a plastic like material able to flow. On Earth it is 2885 km thick. It is made of silicate rocks rich in iron and magnesium. Above the mantle is the crust.

The forces which drive continental drift seem to come from the mantle. The hot rock which boils up at mid-ocean ridges comes from the upper mantle. This rock spreads out forming new oceanic plates. When these meet the continents they plunge back down into the mantle, sometimes going down as far as the outer core.

In addition there are hot spots which start at the outer core and rise up through the mantle to form islands such as Hawaii or Iceland.