Therefore at this time gravity concentrated the densest material in the center and the lighter material rose to the top. The lithosphere is the outer layer of solid rock, containing the crust and the top part of the mantle. When the Earth cooled, the lithosphere cracked into plates which now move around forming continents, etc. This movement is called continental drift or plate tectonics. The lithosphere determines what we see on the surface of the planet.
Thick lithosphere means boring.
Size of lithosphere determined by the internal temperature of the planet. Heat transported outward by conduction and convection. Conduction is the main process for transporting heat through the lithosphere. Heat transfer when two solids are in contact with each other. The hot material expands, gets less dense, and rises.