from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A zone of the earth's mantle that lies beneath the lithosphere and consists of several hundred kilometers of deformable rock.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The zone of the Earth's upper mantle, below the lithosphere.
from the GNU version of the Collaborative International Dictionary of English
- n. the lower layer of the earth's crust, below the lithosphere. It is estimated as from fifty to several hundred miles thick. It is less rigid than the lithosphere, but still rigid enough to transmit some transverse seismic waves.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the lower layer of the crust
This was cool becuase we looked at how upper crust interaction ie mountain building events are affected by the underlaying interaction of the crust and upper mantle - he actually mentioned the word asthenosphere which I haven't heard since like A'level geology I swear!
They travel at a speed of about 5 to 7 kilometers per second through the lithosphere and about 8 kilometers per second in the asthenosphere.
In any one region, the asthenosphere is slowly moving in a consistent direction, and then circling back in the opposite direction down in its deeper layers.
The asthenosphere is weak in the sense that it is not rigid and brittle like the rocky plates of the lithosphere but behaves somewhat like a liquid: yielding, like putty or toffee, if not necessarily molten.
The asthenosphere, in its capacity as a quasi-liquid, has convection currents that extend throughout its whole surface, under the entire area of the plates.
The upper layer of asthenosphere under the South American plate, for example, is moving inexorably westward.
The plates constitute the hard lithosphere – literally, ‘sphere of rock’ – which floats atop the hot, semi-molten asthenosphere – ‘sphere of weakness’.
Near the top of the mantle is a region of partially melted rock called the asthenosphere.
The lithosphere, and therefore, the earth's crust, is not a continuous shell, but is broken into a series of plates that independently "float" upon the asthenosphere, much like a raft on the ocean.
The layer of the mantle above the asthenosphere plus the entire crust make up a region called the lithosphere.