Image Source: Pearson Prentice Hall, Inc.

Main silicate-rich zone within a planet between the crust and metallic core. The mantle accounts for 82% of Earth’s volume and is composed of silicate minerals rich in Mg. The temperature of the mantle can be as high as 3,700 °C. Heat generated in the core causes convection currents in the semi-liquid mantle; rock rises and then slowly sinks again as it cools, driving the tectonic plates. The crust-mantle boundary, which occurs at an average depth of ~32 km, is called the Mohorovicic discontinuity The core-mantle boundary (CMB), the Gutenburg discontinuity, lies at an average depth of 2,900 km.The mantle is subdivided into upper and lower mantle, based upon changes in seismic wave velocity. The uppermost non-convecting mantle comprises the lower part of the lithosphere. Beneath the lithosphere at ~72–250 km depth, is the low-velocity zone; also called the asthenosphere. A rapid increase of seismic velocities occurs at a depth of ~670 km; this corresponds to a mantle phase change. Seismic velocities in the upper mantle are overall lower than those of the lower mantle, indicating that the lower mantle is much denser than the upper mantle. Other smaller changes in velocity correspond to other phase changes.

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Some or all content above used with permission from J. H. Wittke.

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