Image credit: Massey University.
The asthenosphere is the uppermost layer of the mantle of a rocky planet, located below the lithosphere. On Earth, this zone of soft, easily deformed rock lies at depths of about 100 to 250 kilometers. It 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.