This zone is about 2900 km thick and constitutes the great bulk of Earth (82% of its volume and 68% of its mass).
The mantle is composed of silicate rocks (compounds of silicon and oxygen) that also contain abundant iron and magnesium.
Fragments of the mantle have been brought to the surface by volcanic eruptions. Because of the pressure of overlying rocks, the mantle’s density increases with depth from about 3.2 g/cm3 in its upper part to nearly 5 g/cm3