The decomposers are of two kinds, aerobic decomposers and anaerobic decomposers. The aerobic decomposers need the oxygen from the air to break down the dead and decaying matter into simple salts, sugars and hydrocarbon gases. The anaerobic decomposers do not require oxygen for the break down of dead and decaying matter. They break down the matter into various forms of hydrocarbons, sulphides and nitrogenous compounds.
When a dead and decaying matter gets buried deep within the Earth where there is an absence of the decomposers, it takes the form of crude oil, coal, peat, asphalt, and natural gas. The matter gets compressed by the weight of the rocks above and changes its form.
