Coal’s transportability and its availability signaled a shift from an organic economy of muscle, wood, wind and water to a mineral economy that would initially be dominated by coal production and consumption but eventually include petroleum and natural gas. Coal is the product of solar energy formed by decaying giant tree ferns and other vegetation that flourished in the great hot delta swamps of the Paleozoic Era, some 300 million years ago. Over the many thousands of years, volcanic eruptions, uplift, subsidence and flooding covered the vegetation with thick layers upon layers of alluvial mud. Under the weight of these sediments, the pressure and heat characteristic of all chemical processes over the millennia converted the vegetation into rock, shale and a variety of carbon-rich substances. The Industrial Revolution transformed all economies that depended on coal to power its industries. Viewed by most as an inexhaustible energy source, it can easily be cited as an energy revolution.