The upper mantle is a layer of rock inside the Earth that begins just beneath the crust and extends to a depth of about 410 kilometers (255 miles) . It is mostly solid, but its more malleable regions contribute to tectonic activity. Two parts of the upper mantle are often recognized as distinct regions in Earth’s interior: the lithosphere and the asthenosphere. The lithosphere is the solid, outer part of Earth, extending to a depth of about 100 kilometers (62 miles) . The lithosphere includes both the crust and the brittle upper portion of the mantle. The asthenosphere, on the other hand, is located just below the lithosphere and is made up of rock that is fluid and deformable. The upper mantle is known for driving tectonic plate movement, as circular convection currents make tectonic plates slide past one another, sink, rise, and fall.