A modern underground coal-excavating machine Along with oil and gas, coal is a fossil fuel. It is a rock that was formed from the remains of living things that died millions of years ago and are preserved as fossils. Coal was first mined as a fuel on an industrial scale in the 18th century, when it was used in furnaces to power steam engines and smelt iron. Today it is used in power stations to produce electricity. Coke, a baked form of coal, is a smokeless fuel used in making iron and steel.
Formation of coal
Coal began to form about 350 million years ago. Then, parts of the Earth’s surface were covered with swamps where trees and giant ferns grew. When these plants died, they rotted down and gradually changed into a dark soil called peat (1).
As the centuries passed, the peat was buried under layers of sand and mud (2). Successive layers pressed down more and more tightly until the peat was compressed into layers of hard, black, shiny rock: coal (3). Folding and faulting of rock layers, the result of Earth movements over millions of years have brought some coal layers close to the surface (4).
There are different types of coal. Lignite, or brown coal, is the youngest type. It is formed from compressed peat and has the lowest carbon content. Bituminous coal is formed from layers of lignite that have been squeezed, and is the type of coal most used to generate electricity in power stations. Anthracite, which is almost pure carbon, has formed where the layers of lignite were pressed together with the greatest force.
Coal produces around 40% of the world’s electricity.
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