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asthenosphere

[as-then-uh-sfeer]
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noun Geology.
  1. the region below the lithosphere, variously estimated as being from fifty to several hundred miles (eighty-five to several hundred kilometers) thick, in which the rock is less rigid than that above and below but rigid enough to transmit transverse seismic waves.
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Origin of asthenosphere

1910–15; < Greek asthen(ḗs) frail (see asthenia) + -o- + -sphere
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for asthenosphere

asthenosphere

noun
  1. a thin semifluid layer of the earth (100–200 km thick), below the outer rigid lithosphere, forming part of the mantle and thought to be able to flow vertically and horizontally, enabling sections of lithosphere to subside, rise, and undergo lateral movementSee also isostasy
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Word Origin

C20: from astheno-, from Greek asthenēs weak + sphere
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for asthenosphere

n.

layer of the Earth's upper mantle, 1914, from Greek asthenos (see asthenia) + sphere.

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Online Etymology Dictionary, © 2010 Douglas Harper

asthenosphere in Science

asthenosphere

[ăs-thĕnə-sfîr′]
  1. The upper part of the Earth's mantle, extending from a depth of about 75 km (46.5 mi) to about 200 km (124 mi). The asthenosphere lies beneath the lithosphere and consists of partially molten rock. Seismic waves passing through this layer are significantly slowed. Isostatic adjustments (the depression or uplift of continents by buoyancy) take place in the asthenosphere, and magma is believed to be generated there. Compare atmosphere hydrosphere lithosphere.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.