Why do the earth's tectonic plates move? Scientists have hypothesized that, like the movement of heat through air and water (convection), the material in the mantle, hot at the bottom, cool at the top, flows in a convection current. As the tectonic plates float on the mantle, they behave as a float on the ocean would, moving in the same direction as the mantle's material is flowing.

Why is the mantle hot at the bottom and cooler at the top? Heat, pressure and density all increase as you go deeper into the earth, with the inner core being the hottest layer with the most pressure and density. The crust would be the coolest layer, with the least pressure and density.