How coal is formed

Coal is considered to be a fossil fuel, like oil and natural gas. Fossil fuels are made up of plants and animals that lived and died millions of years ago at a time when dinosaurs ruled the earth.

At the time of the dinosaurs, swamps, gigantic trees and plants covered the earth. As the plants died, they were covered by sand and mud. Thick layers formed and they buried prehistoric forests and seas. Underneath the sand and mud, the plants created, a soggy, sponge-like material called peat. Over several thousand years, the peat was buried by sand and silt that put a lot of pressure on the peat and compressed it under the earth’s surface. As more layers were made, the peat was pushed tighter and tighter, like trash in a trash compactor. The increased pressure and heat from the earth eventually turned the peat into coal. Coal deposits can be traced to different time periods, but the most abundant deposits are from more than 300 million years ago.

Coal is now classified into four different categories. The differences in the types of coal are based on the amount of carbon in the coal and how it responds to increasing heat and pressure beneath the earth’s surface. The four types of coal are: Lignite, Subbituminous, Bituminous and Anthracite. Kennecott Energy extracts low-sulfur, subbituminous coal. This type of coal is primarily used to produce steam for electricity generation.