How Coal was formed?

Formation of coal has been one of the most interesting stories we were told by our teachers during our primary schools. About 300 million years ago, the earth had dense forests in low-lying wetland areas. Due to natural processes such as flooding, these forests were buried under the soil.

As more and more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. For the process to continue, the plant matter was protected from biodegradation and oxidization, usually by mud or acidic water. This trapped the carbon in immense peat bogs that were eventually covered and deeply buried by sediments. Under high pressure and high temperature, dead vegetation was slowly converted to coal.

• As coal contains mainly carbon, the conversion of dead vegetation into coal is called carbonization.
• The wide, shallow seas of the Carboniferous era provided ideal conditions for coal formation, although coal is known from most geological periods. The exception is the coal gap in the Permian–Triassic extinction event, where coal is rare.
• Please note that Coal is also known from an era where there were no land plants such as from Precambrian strata. This coal is presumed to have originated from residues of algae.
• The Hit’s law says that in a small area, the deeper the coal, the higher its rank (grade). The law holds true if the thermal gradient is entirely vertical, however, metamorphism may cause lateral changes of rank, irrespective of depth.