What is Coal?

During the Carboniferous Period of Earth’s geologic history , between 290 and 350 million years ago, in many parts of the world there existed warm and humid climatic conditions. These conditions favored the growth of huge tropical ferns and giant trees, which grew and died in vast swamp areas. The dead plants fell into the boggy waters, which tended to exclude oxygen and bacteria, so that they only partially decomposed to produce a peat-like material. This fossilized plant debris was the beginning of coal.

Vegetation continued to grow for many generations and centuries, forming vast, thick peat beds, which were later to turn into coal. After a time the areas of swamp gradually became submerged by shallow seas, where they were covered by sediment. These sediments would later become sedimentary rock. This cycle of swamp followed by submersion was often repeated a number of times, so that a sequence of horizontal bands of peat and inorganic, sedimentary rock was built up. This formed the first stage, called the biochemical stage. Coal formation occurred in other geologic periods as well.

Subsequently, the bands of peat were altered by the action of pressure and temperature during the second, or geochemical stage, to form the various kinds of coal found today. As much as a 20-fold reduction in the thickness of the original plant deposits sometimes occurred. During the course of time these horizontal coal seams were further altered as they became folded, tilted and eroded. Much of this action was due to the motion of the continents, as mountains formed and were then worn away.