What Kind of Coal?
Coal is a fossil fuel and therefore non-renewable. A combustible, sedimentary, organic rock composed mainly of carbon, hydrogen, and oxygen, it was formed from vegetation consolidated between other rock strata and altered by the combined effects of pressure and heat over millions of years. While oil and gas were formed primarily from enormous quantities of microscopic plants (algae) that fell to the bottoms of prehistoric seas, coal is the altered remains of ancient vegetation that accumulated in swamps and peat bogs (peat currently covers 3 percent of Earth’s surface; in previous geologic eras, that percentage was much higher). While oil and gas were formed during two relatively brief periods of intense global warming, roughly 150 and 90 million years ago, coal formation started much earlier and occurred during much longer time spans, with the first primary formation period occurring during the late Carboniferous period (roughly 360 to 290 million years ago), another in the Jurassic-C
