Fossil Fuels

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•  Peat forms when organic matter is not fully decomposed because of acidic and / or anaerobic conditions in

    waterlogged soils


carbon fuels

Partial Decomposition

In many soils, saprotrophic bacteria and fungi will decompose dead organisms and return nutrients to the soil for cycling

  • This decomposition process requires oxygen (cell respiration is required to fuel digestive reactions)

Waterlogged regions may lack oxygenated air spaces within the soil and thus possess anaerobic conditions

  • Anaerobic respiration by organisms in these regions produces organic acids (e.g. acetate), resulting in acidic conditions 
  • Saprotrophic bacteria and fungi cannot function effectively in anaerobic / acidic conditions, preventing decomposition

Coal Formation

Since the organic matter is not fully decomposed in waterlogged soils, carbon-rich molecules remain in the soil and form peat

  • When deposits of peat are compressed under sediments, the heat and pressure force out impurities and remove moisture
  • The remaining material has a high carbon concentration and undergoes a chemical transformation to produce coal

How Coal is Formed

coal formation

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•  Partially decomposed organic matter from past geological eras was converted into either coal or into oil and gas

    which accumulates in porous rocks


Oil / Natural Gas Formation

Oil (i.e. petroleum) and natural gas form as the result of the decay of marine organisms on the ocean floor

  • Sediments (e.g. clay and mud) are deposited on top of the organic matter, creating anoxic conditions that prevent decomposition
  • As a result of the burial and compaction, the organic material becomes heated and hydrocarbons are formed
  • The hydrocarbons form oil and gas, which are forced out of the source rock and accumulate in porous rocks (e.g. sandstone)

The formation of fossil fuels (coal, oil and gas) takes place over millions of years, making them a non-renewable energy source

How Oil and Gas are Formed

oil formation