Here's a breakdown:

* Lithosphere: This is the rigid outer layer of the Earth, composed of the crust and the uppermost part of the mantle. It's broken into tectonic plates.

* Asthenosphere: This is a semi-molten, partially solid layer beneath the lithosphere. It's like a very viscous fluid, allowing the tectonic plates to move on top of it.

* Mesosphere: This is the solid layer below the asthenosphere. It's strong and rigid, but still hotter than the asthenosphere.

The movement of tectonic plates is driven by convection currents within the asthenosphere. The heat from the Earth's core causes the asthenosphere to move in a circular pattern, like a giant conveyor belt. This movement drags the plates along with it, causing them to collide, separate, or slide past each other.