Asthenosphere
In an Earth-like planetary body, the zone of the upper mantle that exhibits plastic properties. This subsurface layer that is more plastic than adjacent layers because the combination of pressure and temperature places it near (or slightly above) the melting point. Asthenospheric movements may disrupt the planet's surface In an Earth-type planet, it is located below the lithosphere. On Old Earth the asthenosphere is between about 100 and 250 kilometers deep, but on other worlds this figure can vary fairly markedly.
 
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Development Notes
Text by M. Alan Kazlev

Initially published on 07 October 2001.