 so that the crust will sort of slide over the mantle. So the earth consists of the crust, the outer crust, and then that rests on the mantle. And the mantle is semi-liquid, so there's some friction, but there's also some movement over it. Plate tectonics is an example of that. And then you go deeper and there's the core, the inner and outer core that generates the geomagnetic field.