What the plastic like layer of the upper mantle on which the lithosphere floats?

The plastic-like layer of the upper mantle on which the lithosphere floats is called the asthenosphere. It is characterized by its semi-fluid properties, allowing the rigid lithospheric plates above to move slowly over it. This movement is driven by convection currents within the mantle, influencing tectonic activity and the formation of geological features. The asthenosphere plays a crucial role in the dynamics of plate tectonics.