Today scientists believe that the crust and the rigid, outer zone of the mantle makes up a layer that is called the Lithosphere . The lithosphere is broken into 12 large pieces that are called plates. The zone directly under the lithosphere is made of a flowing, denser layer called the Asthenosphere. Scientists believe that the plates ride on the asthenosphere, which flows due to convection currents. See diagram on page 2.
, a German geologist, believed that the Outer Core must be made of a liquid because the slower S (secondary waves) could not pass through this layer and in fact "bounced off" and were deflected many degrees off course. Study diagram A on page 3.