Part of Hall of Planet Earth.
Deep beneath our feet is a 2,900-kilometer-thick (1,800-mile) layer of mostly solid rock called the mantle. The mantle flows slowly due to convection. In convection, hotter rocks, which have relatively low densities, rise, while cooler rocks with higher densities sink. In this globe, the hottest portions of the mantle (yellow) are rising toward the surface and cooler portions (red) are sinking toward the core.