THE ENERGY HIDDEN IN ROCKS

Granite is one of the most common and well-recognized rocks to occur at the surface of the Earth. Let us suppose that we put a fragment of granite in a small container, which is then completely sealed. We will assume that the container is made of an ideal thermally insulated material, and that heat can neither escape from within nor enter from outside. What changes will occur in the granite inside the box?

If the contents of the box were examined after one or two years, probably no changes at all would be observed. However, if it were examined after the passage of several hundreds or thousands of years, a careful observer would no doubt realize that the temperature within the container was rising very slightly. After a few hundred thousand years, this rise in temperature would be apparent to any observer. If the calculation described later is carried out, it is clear that the granite in the sealed container would melt completely after several tens of millions of years owing to the rise in temperature.