The mantle is a part of an astronomical object. The interior of the Earth, similar to the other terrestrial planets, is chemically ivided into layers. The mantle is a highly viscous layer directly under the crust, and above the outer core. Earth's mantle is a ~2,900 km thick (1,800 miles) rocky shell comprising approximately 70% of Earth's volume. It is predominantly solid and overlies the Earth's iron-rich core, which occupies about 30% of Earth's volume. Past episodes of melting and volcanism at the shallower levels of the mantle have produced a very thin crust of crystallized melt products near the surface, upon which we live. The gases evolved during the melting of Earth's mantle have a large effect on the composition and abundance of Earth's atmosphere.