Lower mantle, internal Earth structure. Artwork showing the appearance of the Earth's lower mantle. This is a region of high temperatures and pressure. The magma has a viscosity greater than in the upper mantle. The internal structure of the Earth is divided into the outer crust, the upper and lower mantle, and the outer and inner core. For examples of the material composition of each layer of the Earth, see images C018/0208 to C018/0212.