The asthenosphere is the layer of the Earth that lies below the lithosphere. It is a layer of solid rock that has so much pressure and heat the rocks can flow like a liquid. The rocks are less dense than the rocks in the lithosphere. This allows the tectonic plates in the lithosphere to move around on the Earth's surface by "floating" on the rocks that are slowly flowing like a liquid.
The lithosphere is where the plates float and move .It is the upper layer of the earth's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.