What happens to the old ocean floor while new floor is being made?

This process is known as sea floor spreading. As new oceanic floor is being created the old floor is destroyed and through the process of subduction is taken back to the molten core of the earth where it starts its life cycle all over again. It will be recycled and one day will emerge in a fresh layer of molten material creating new sea floor.

South wales composes a lot of coal in that region.