The asthenosphere is an important layer, or zone, within the earth. Temperature increases with depth in the earth and eventually the rock material of the mantle becomes partially molten. This partially molten layer is called the asthenosphere. Because it is partly molten (perhaps up to 10%) it becomes pliable or "plastic". Rock here is hot enough to flow very slowly without fracturing, similar to the way Silly Putty® or warm butter oozes. The rigid lithospheric plates, whih consist of mantle material that is solid and crust, ride on the flowing asthenosphere. Denser oceanic plates can be subducted back into the asthenosphere where they slowly melt and are reincoporated. Recently obtained images using seismic waves (similar to taking a sonogram) have found completely submerged old lithospheric plates that are still extant in the asthenosphere.
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