Formation of Coal

The Carboniferous World

Approximation of the Earth during part of the Carboniferous Era

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The Carboniferous World
Public Domain image

The Carboniferous World

Approximation of the Earth during part of the Carboniferous Era

Public Domain image

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Coal is formed from the accumulation of dead plant vegetation in areas that have low oxygen, such as a bog or moor.

The formation of coal began millions of years ago when huge areas of swampland formed across much of the world, including Ireland . Changes in climate, especially increasing annual rainfall, created these very soggy, wet grounds. It is believed that entire forests sank below the water and were subsequently covered and compressed by large quantities of sand and mud.

As there is very little oxygen in boggy areas where coal forms, the vegetation is prevented from decomposing quickly. In the absence of decomposition, dead vegetation builds up, layer upon layer and becomes buried deeper underground. These layers of material undergo changes when heat and pressure from the overlaying ground are applied and the material becomes compressed. The water content is reduced while the chemical composition of the material changes to increase its carbon content.

Over time, coal develops in different stages and is usually classified into three grades.