mantle

mantle portion of the earth 's interior lying beneath the crust and above the core. No direct observation of the mantle, or its upper boundary, has been made; its boundaries have been determined solely by abrupt changes in the velocities and character of seismic waves passing through the earth's interior (see seismology ). Samples of the upper mantle may be provided by some volcanic eruptions in ocean areas, e.g., the Hawaiian Islands. The continental and ocean crusts, along with part of the solid upper mantle, make up the lithosphere to a depth of about 62 mi (100 km). Within the lithosphere is the Mohorovičić discontinuity, or Moho, considered to be the mantle's upper surface, at depths ranging from 4 to 43 mi (7 to 70 km). Analysis of seismic waves indicates that rocks below the Moho are less rigid and slightly more dense than rocks making up the crust. A zone of low seismic velocity and rigidity just below the lithosphere, called the asthenosphere , is present in the upper part of the mantle, from 62 mi (100 km) to 156 mi (250 km). Its presence is of critical importance to plate tectonics . The mantle continues to the Gutenberg discontinuity at the liquid outer core, with the base of the mantle located about 1,800 mi (2,900 km) below the earth's surface. The entire mantle constitutes about 84% of the earth by volume. Its composition is thought to be similar to peridotite, an igneous rock of mostly magnesium-rich silicate.

mantle
1. Zone lying between the Earth's crust and core, approximately 2300 km thick. The mantle is probably similar in composition to garnet peridotite and it represents about 84% of the Earth's volume and 68% of its mass. A mantle is present in most terrestrial planets and the Moon, but is of a different composition in each case.

2. (pallium) In Brachiopoda and Mollusca, a layer of tissue that covers the body and is responsible for the secretion of the shell.

mantle Layer of the Earth between the crust and the core, which extends to a depth of 2890km (1795mi). The mantle forms the greatest bulk of the Earth: 82% of its volume and 68% of its mass. The uppermost part is rigid, solid and brittle and, together with the Earth's crust, forms the lithosphere. Between a depth of about 60km (40mi) to 200km (125mi), the mantle has a soft zone that is called the asthenosphere. Here, temperature and pressure are in balance so that much of the mantle material is near melting point or partly melted and capable of flowing. 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. The chemical constitution of the mantle is uncertain, but it is thought to be made up of iron-magnesian silicates.