The layer of the Earth that lies directly below the crust is called the mantle. The mantle is composed of semi-solid rock and extends approximately 2,900 kilometers below the surface to the outer core. It plays a crucial role in plate tectonics and the movement of Earth's lithospheric plates. The mantle's convection currents drive these movements, leading to geological phenomena such as earthquakes, volcanic eruptions, and the formation of mountain ranges. The temperature and pressure increase with depth, influencing the physical state and behavior of the mantle materials.