The Evolution of the Earth

The crust of the earth is not one whole piece, like an egg shell. It's actually cracked in a lot of places. But then even if you crack it and break it the shell into several pieces, you still have to wonder how those pieces can move about. The reason is that they're sort of floating on semi-liquid mantle, right, on rock that is fluid. Each plate is like flowing in some direction on top of liquid. And where it hits another plate, it's being subducted down back into the earth. So it's sort of like very slow moving conveyor belt where you're destroying a plate on one side and creating more plate on the other side.