The Layer of the Earth's Interior(2) The asthenosphere: The region of the mantle where rocks become ductile, have little strength, and are easil deformed. It lies at a depth of 100 to 350 km below the surface The Lithosphere The outer 100 km of the solid earth where rocks are harder and more rigid than those in the plastic asthenosphere.The Layer of the Earth’s Interior (2) ◼ The Asthenosphere: ◼ The region of the mantle where rocks become ductile, have little strength, and are easily deformed. It lies at a depth of 100 to 350 km below the surface. ◼ The Lithosphere: ◼ The outer 100 km of the solid Earth, where rocks are harder and more rigid than those in the plastic asthenosphere