Here's a breakdown:

* Lithosphere: The rigid outer layer of the Earth, composed of the crust and the uppermost part of the mantle.

* Asthenosphere: A semi-molten, partially solid layer in the upper mantle. It is weaker and more ductile than the lithosphere, allowing the plates to move.

The movement of tectonic plates is driven by convection currents within the mantle. Hotter, less dense material rises, while cooler, denser material sinks, creating a cycle of movement that drags the plates along with it.