Asthenosphere

noun

1. A zone of the earth's mantle that lies beneath the lithosphere and consists of several hundred kilometers of deformable rock.
2. 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.
3. The zone of the Earth's upper mantle, below the lithosphere.
4. the lower layer of the crust