Here's a breakdown:

* Lithosphere: This is the rigid, outermost layer of Earth. It includes the crust and the uppermost part of the mantle.

* Asthenosphere: This is a semi-solid layer of the upper mantle located beneath the lithosphere. It's characterized by being partially molten and having a weaker, more fluid-like consistency compared to the lithosphere.

The asthenosphere is crucial for plate tectonics. The lithospheric plates "float" on the asthenosphere, and their movement is driven by convection currents within this layer.