Composition. (We use the crust-mantle-core terminology to describe differences in chemical composition in Earth's interior. We use the lithosphere- asthenosphere terminology to describe differences the physical state and behavior. Note that the boundaries between layers with different compositions do not occur at the same depths as the boundaries between layers with different physical properties. For example, there is a change in composition when passing from crust into mantle. But there is no change in physical state or behavior at this boundary- the uppermost part of the mantle behaves in the same way that the crust does because it is still far enough below its melting temperature to be a rigid, brittle solid. The transition to a softer, more pliable solid occurs further down within the mantle and this change in behavior occurs with no change in composition.)