Upper mantle, internal Earth structure. Artwork showing the appearance of solid and molten rock (lava) in the Earth's upper mantle. The magma viscosity in the upper mantle is lower than in the lower 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.