Earth's tectonic plates float on a layer beneath them called the asthenosphere. The asthenosphere forms the base of the tectonic plates, which contain many different layers. This layer forms from a buildup of dense rock created from semi-solid materials, and it comprises a layer of Earth's mantle.
The asthenosphere contains materials more dense than those of the tectonic plates lying above, which enables the plates' flotation. The positioning of tectonic plates above the asthenosphere and resulting movement is just one small part of how tectonic plates work. The Earth's crust forms from many other layers of sedimentary deposit, which form above and below the asthenosphere. Above the asthenosphere lies the lithosphere, which occurs in continental and oceanic forms.
The continental variety contains materials of lighter weight than those in the oceanic form. Tectonic plates might form from either substance. Regardless of composition, all plates have the same ability to move via flotation. The movement of tectonic plates varies depending on several factors, including weight and size. Heavier plates, or plates with heavier areas, sink more quickly than lighter ones. Over time, these plates dissolve into the lithosphere. One plate might sink beneath the edge of another, causing a subduction zone. Fluids from moving plates rise to the surface, escaping into surrounding water or air, ultimately producing magma and lava.