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lithosphere vs. asthenosphere

[ lith-uh-sfeer ]
noun
  1. the solid portion of the earth (distinguished from atmosphere, hydrosphere).
  2. the crust and upper mantle of the earth.
[ as-then-uh-sfeer ]
noun
  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.