How is Coal Formed

Debopriya Bose Jun 18, 2019
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Plants that got buried in swamps millions of years ago, eventually developed into coal under anaerobic conditions. Learn more about the formation process in the following post.
Coal is a fossil fuel, that was formed millions of years ago, deep within the Earth's crust. It is a readily combustible fossil fuel, that is formed from dead plant matter of the Carboniferous Period. It is primarily composed of carbon.
However, it may also contain other elements like sulfur, hydrogen, oxygen, and nitrogen, in varying amounts. It is the source of fuel that meets most of our electricity requirements. It takes millions of years to form and we have exhausted large reserves of this fossil fuel already. This has sent us into a scurry for finding alternative energy sources.

Formation of Coal

Coal was formed 300 million years ago, when most of the Earth's surface was covered with swamps. Terrestrial plants, mainly tall trees of swampy forests, like lycopods, the giant ferns, horsetails, and club mosses, died and fell in these swamps or shallow bodies of water.
Due to climatic changes and catastrophic events, large amounts of forests sank into these swamps. These layers got covered with large quantities of mud and sand. As a result, the lower layers of vegetation got compressed to form a soggy, sponge like material called peat.
The event of dead vegetation accumulating in the swamps and getting covered with mud, kept taking place as a cycle. This explains the alternating layers of coal and clay or sandstone (compacted sand) in the substratum. As the dead vegetation got buried in wet and acidic conditions, they also got cut off from direct supply of air.
Hence, the decomposition process got slowed down and what resulted was peat, which is the first stage of coal formation. With more layers of soil and vegetable matter accumulating over peat, oxygen, hydrogen, and water, was squeezed out of it.
With increase in pressure and further compacting between layers of sediments, peat changed into bituminous, subbituminous coal, and finally to refined form. In each step, the newly formed material is more rich in carbon than material in the previous stage.
The process of coal formation is an extremely slow process. The best form of this fossil fuel, with 90 to 95% carbon, belongs to the Carboniferous Period, that dates back to 360 to 250 millions years ago. However, it was also formed in the subsequent ages, like the Permian Period and the Secondary Period, that spanned over 290 to 65 million years ago.
Coal from certain areas formed during the Tertiary Period (65 million years ago to 2.6 million years ago) is also of excellent quality. This is due to the fact that the peat was brought into maturity early by the heat generated due to collision of tectonic plates.

Where is it Found?

Coal is found in seams (veins or coal beds) that may lie within less than 200 feet of the Earth, or even those that are buried more than 1000 feet below the layers of soil. These are accessed through mining. If the deposits are shallow, then they are accessed through surface mining.
The deeper ones, that lie more than 1000 feet deep, are excavated using the process of deep mining or underground mining. However, the fossil fuel that is mined, needs to be processed, which involves removing dirt, rocks, ash, sulfur, and other contaminants. Removal of these impurities results in a increase in the heating value.
As far as the leading producers of coal are concerned, China tops the list. However, it is the United States of America that has the largest reserves. It is followed by Russia, China, and India. However, notable producers in the world are Australia, South Africa, USA, Russia, India, and China.
Although coal meets most of our energy requirements, burning it releases more amount of pollutants than any other form of fossil fuel. This, coupled with the fact that we may soon run out of the reserves of this fossil fuel, is making us consider other forms of fuel that could take its place.