[as-then-uh-sfeer] 
| 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. |
| as·then·o·sphere (ās-thěn'ə-sfîr') n. A zone of the earth's mantle that lies beneath the lithosphere and consists of several hundred kilometers of deformable rock. [Greek asthenēs, weak; see asthenia + sphere.] |
| asthenosphere (ās-thěn'ə-sfîr') Pronunciation Key
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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