Tectonic plates float on the asthenosphere, which is a layer of the Earth's upper mantle.

Here's a breakdown:

* Lithosphere: The rigid outer layer of the Earth, consisting of the crust and the uppermost part of the mantle. This is where the tectonic plates are located.

* Asthenosphere: A semi-molten, ductile layer beneath the lithosphere. The asthenosphere is like a very viscous fluid, allowing the tectonic plates to move slowly over time.

* Lower Mantle: The layer beneath the asthenosphere, which is much more solid.

Think of it like a sheet of ice floating on water. The ice represents the tectonic plates, and the water represents the asthenosphere.