Lexikon

the interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core. Earth's mantle is about 2,900 km thick rocky shell that constitutes about 84 percent of Earth's volume. It is predominantly solid. The mantle is divided into sections based upon results from seismology. These layers (and their depths) are the following: the upper mantle, around 7 to 35 km, downward to 410 km starting from the base of the crust or Mohorovièiæ discontinuity (the boundary between the crust and mantle defined by a contrast in seismic velocity), the transition zone (410–660 km), the lower mantle (660–2891 km), and in the bottom of the latter region there is the anomalous D" layer with a variable thickness (on average ~200 km thick). The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 kilometers below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core. The boundary between the lower mantle and the outer core is defined by the Gutenberg discontinuity (core-mantle boundary).