Several distinct parts of the mantle have been recognized. The uppermost part is rigid, solid, and brittle and together with the Earth's crust forms the lithosphere. The upper mantle also has a soft zone, which is called the asthenosphere. Temperature and pressure are in delicate balance, so that much of the mantle is near melting point, or partially melted and capable of flowing. Recent studies have suggested this layer is responsible for the production of basaltic magmas. The remainder of the mantle is thought to be more solid, but still capable of creeping flow. In the lower mantle, several changes in seismic velocity can be detected, interpreted as phase changes, in which the atomic packing is rearranged into denser and more complex units.
The Gutenberg discontinuity separates the Earth's mantle from the outer core; the Mohorovicic discontinuity separates the uppermost portion of the mantle from the crust.
Related category GEOLOGY AND PLANETARY SCIENCE
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