Plate Tectonics
The theory of plate tectonics says that the
Earth's outer shell is made from plates that glide over
the mantel. These plate movements are driven by movement
and convection in the mantel.
Mantel Convection
We can see that the hot mantel rock rises
to the surface, it then begins to sink again once it has
cooled. This is due to the the laws of thermodynamics at play.