Here's a breakdown:

* Lithosphere: This is the rigid, outermost layer of the Earth, composed of the crust and the uppermost part of the mantle. Tectonic plates are pieces of the lithosphere.

* Asthenosphere: This is a semi-molten, ductile layer located below the lithosphere. It's like a very thick, viscous fluid, allowing the lithosphere to move over it.

The movement of tectonic plates is driven by convection currents within the asthenosphere. Heat from the Earth's core causes the asthenosphere to circulate, dragging the lithospheric plates along with it.