The lithosphere is the rigid outermost layer of the Earth, composed of the crust and the uppermost part of the mantle. It is broken into large pieces called tectonic plates, which move slowly over the underlying asthenosphere.

Here's a breakdown:

* Crust: The outermost layer of the Earth, composed of relatively light, solid rock. It is divided into oceanic crust (thinner and denser) and continental crust (thicker and less dense).

* Mantle: The layer beneath the crust, primarily composed of solid rock but capable of flowing very slowly over long periods. The uppermost part of the mantle is part of the lithosphere.

* Asthenosphere: A partially molten layer beneath the lithosphere, where the rocks are hot and behave like a very viscous fluid. This is the layer on which the tectonic plates "float" and move.

So, the lithosphere, which consists of both the crust and the upper mantle, is the layer that comprises the tectonic plates.