Answer;
-Lithosphere
The lithosphere forms the relatively cool, brittle plates of plate tectonics
Step-by-step explanation;
-Plate tectonics is the theory that Earth's crust is broken up into plates. The tectonic plates are made up of Earth's crust and the upper part of the mantle layer underneath. Together the crust and upper mantle are called the lithosphere and they extend about 80 km deep.
-These plates are actually pieces of the planet's lithosphere, which is the outermost shell of the earth made up of the earth's crust and upper part of the mantle, and for this reason, tectonic plates are sometimes called 'lithospheric plates.'