Which rigid outer layer of Earth is divided into tectonic plates?

The lithosphere is the rigid outer layer of Earth divided into tectonic plates.

It includes Earth’s crust plus the rigid uppermost part of the mantle. Its strength comes largely from being relatively cool and solid compared with the hotter, weaker asthenosphere beneath it. The plates move as coherent slabs over that slowly deforming layer.

Plate boundaries produce familiar geological events. Divergent boundaries pull plates apart, convergent boundaries bring them together, and transform boundaries slide past one another. Earthquakes, volcanoes, mountain ranges, and ocean trenches are concentrated around these boundaries.

A common mix-up is treating the lithosphere as identical to the crust. The crust is only its outer chemical layer; the lithosphere also contains mantle material. The asthenosphere is not the answer because it lies beneath the lithosphere and is mechanically weaker.