Coal formation has been described as “an inefficiency in the carbon cycle,” (Barghoorn, 1952) when carbon from plants remains in terrestrial sediments and is not recycled to the atmosphere (Figure ). Coal is, by definition, a readily combustible rock containing more than 50% by weight and 70% by volume of carbonaceous material (Schopf, 1966). Another definition describes coal as a combustible solid, usually stratified, which originated from the accumulation, burial, and compaction of partially decomposed vegetation in previous geologic ages (Hendricks, 1945)
