Coal consists of volatile matter, moisture and carbon. The carbon burn while the volatile matter and moisture are removed. Coal after burning produces heat which is used for various purposes.
Coal is the result of decomposition and conversion of plants and other living matter. Coal was formed about 25,00,00,000 years ago. Parts of the earth at the time were covered by swamps and large trees. When the trees had died they sank into the swamps. Mud and sand settled on them. This cycle continued for millions of years. Due to the great pressures in inner part of the earth, the burnt trees were transformed into coal. Even centuries before the birth of Christ, man has been using coal.
Coal comprises three-fourths of the total fossil fuels of the world. The problems of using coal are mainly that the burning of coal for energy gives rise to carbon dioxide.