The mantle is the mostly solid, rocky layer that lies beneath Earth's crust and above the outer core. It's about 2,900 kilometers (1,800 miles) thick and makes up 84% of Earth's total volume. The mantle is hot, with temperatures ranging from around 1,000°C (1,800°F) at the top to over 4,000°C (7,200°F) at the bottom. Despite the heat, the immense pressure keeps most of the mantle in a solid state, although it behaves like a very viscous fluid over long periods. This slow, creeping movement of the mantle drives plate tectonics, which shapes Earth's surface and influences volcanic activity.