The layer of Earth beneath the crust is called the mantle. The mantle is a solid layer of rock that is about 2,900 kilometers (1,800 miles) thick. It is divided into two parts: the upper mantle and the lower mantle. The upper mantle is about 670 kilometers (420 miles) thick and is made up of rocks that are rich in magnesium and iron. The lower mantle is about 2,230 kilometers (1,385 miles) thick and is made up of denser rocks that are rich in silicon and oxygen. The mantle is hot and dense, but it is not as hot as the Earth's core.