Of all the fossil fuels, coal is the most plentiful. It is also the most damaging to the environment. When beds of coal were being formed, Earth must have been a vastly different place from what it is now. Coal is found in the most unlikely places, including Antarctica. Probably it was not formed there, so there must have been some serious upheavals on Earth to transport the deposits to that region, so inhospitable now to growing vegetation.
Coal is widely, but unevenly, distributed globally. The United States, Russia, and China have about 80 percent of the known deposits. The amount of coal available is known better than the stores of the other fossil fuels, oil, and natural gas. It is presumed most of the deposits are now known. Their capacities have been measured by digging holes into a deposit some distances apart and estimating the quantity of coal in that deposit. In estimating coal reserves, the experts double the amount of known reserves and then add some factor for future discoveries. The amount so estimated is not a mea sure of how much can be mined economically, however. For economic recovery the seam must be at least 60 centimeters (24 inches) thick and no deeper that 2000 meters (6500 ft.), unless the coal can be recovered by strip mining, to be discussed later.
Despite the uncertainties in these estimates one can say that enough coal is available to last for several hundred years at the present rate of use. It could probably last for over 100 years if it were the sole source of energy at the present level of use. Dependable