mantle(redirected from mantle zone)
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mantle,portion of the earthearth,
in geology and astronomy, 3rd planet of the solar system and the 5th largest, the only planet definitely known to support life. Gravitational forces have molded the earth, like all celestial bodies, into a spherical shape.
..... Click the link for more information. '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 seismologyseismology
, scientific study of earthquakes and related phenomena, including the propagation of waves and shocks on or within the earth by natural or artificially generated seismic signals.
..... Click the link for more information. ). 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 lithospherelithosphere
, brittle uppermost shell of the earth, broken into a number of tectonic plates. The lithosphere consists of the heavy oceanic and lighter continental crusts, and the uppermost portion of the mantle.
..... Click the link for more information. 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 asthenosphereasthenosphere
, region in the upper mantle of the earth's interior, characterized by low-density, semiplastic (or partially molten) rock material chemically similar to the overlying lithosphere.
..... Click the link for more information. , 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 tectonicsplate tectonics,
theory that unifies many of the features and characteristics of continental drift and seafloor spreading into a coherent model and has revolutionized geologists' understanding of continents, ocean basins, mountains, and earth history.
..... Click the link for more information. . 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.
mantleThe zone within a planet or satellite, lying below the crust. See also Earth.
one of the shells of the earth that lies directly under the earth’s crust. The mantle is isolated from the crust by the Mohorovičić discontinuity, which is found under the continents at a depth of 20 to 80 km (on the average, 35 km) and under the oceans at a depth of 11 to 15 km below the water’s surface. The distribution speed of seismic waves (used as an oblique means of studying the internal structure of the earth), upon crossing from the crust to the mantle, increases abruptly from about 7 to 8 km per sec. The base of the mantle is believed to lie at a depth of 900 km (where the mantle is divided into upper and lower parts) or at a depth of 400 km (where it is divided into upper, middle, and lower parts). The zone between 400 and 900 km deep is called the Golitsyn layer.
The mantle is probably made of granite peridotites, with mixtures in the upper parts of eclogites. An important characteristic of the structure of the mantle is the presence of a zone of reduced seismic wave speed. There are differences in the structure of the mantle under the different tectonic zones—for example, under geosynclines and platforms. Processes develop in the mantle that are the sources of tectonic, magmatic, and metamorphic phenomena in the earth’s crust. The mantle is accorded an important role in many tectonic hypotheses. For example, it has been suggested that the earth’s crust was formed by a process of smelting from the substance of the mantle and that tectonic movements are connected with movements in the mantle.
REFERENCESMagnitskii, V. A. Vnutrennee stroenie i fizika Zemli. Moscow, 1965.
Belousov, V. V. Zemnaia kora i verkhniaia mantiia materikov. Moscow, 1966.
Belousov, V. V. Zemnaia kora i verkhniaia mantiia okeanov. Moscow, 1968.
V. V. BELOUSOV
(in biology). (1) A fold in the skin of certain invertebrate animals (mollusks, brachiopods, and barnacles) that encloses the body of the animal completely or in part.
In most cases the external skeleton of the animal is secreted by the mantle. Between the body and the mantle is the mantle cavity, which is connected to the outside environment and into which the kidneys, sexual glands, and rectum open. In the mantle cavity are the respiratory organs (gills) and certain sense organs. In aquatic animals the mantle is usually lined with ciliated epithelium; the beating of the cilia creates a current of water through the mantle cavity. This current delivers oxygen and food particles and carries off metabolic products. In some gastropod mollusks there are networks of blood vessels in the walls of the mantle, forming a kind of “lung.” In cephalopod mollusks the mantle is muscular and is used to expel a stream of water through a special funnel, giving the animal jet propulsion.
(2) The mantle, or tunica, is part of the formative tissue (meristem) in the growing point (apex) of the stem of plants. The inner layers of mantle cells divide both perpendicularly to the surface of the apex, that is, anticlinally, and parallel to the surface of the apex, that is, periclinally (in this case the inner part of the apical cells is called the corpus). Subsequently, the epidermis and primary cortex differentiate from the mantle, and the axis cylinder differentiates from the corpus.