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[as-then-uh-sfeer] /æsˈθɛn əˌsfɪər/
noun, Geology.
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.
Origin of asthenosphere
1910-15; < Greek asthen(ḗs) frail (see asthenia) + -o- + -sphere Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for asthenosphere


/əsˈθiːnəˌsfɪə; -ˈθɛn-/
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 movement See also isostasy
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
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Word Origin and History for asthenosphere

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

Online Etymology Dictionary, © 2010 Douglas Harper
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asthenosphere in Science
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.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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