The asthenosphere is solid upper mantle material that is so hot that it behaves like plastic and can flow. The lithosphere rides on the asthenosphere. The asthenosphere is solid but it can flow, like toothpaste. The asthenosphere and Lithosphere constitute the utmost concentric layers of our earth. The asthenosphere encompasses much of the upper mantle of the earth. Then, the lithosphere comprises the uppermost mantle as well as the overlying crust. Thus, we see both of these things comprise different things. The rocks found in this zone which are mostly peridotite are quite solid in structure. The asthenosphere is the zone of the earth which lies beneath the lithosphere. It is said to be hotter and more fluid than the lithosphere.