What are Fossil Fuels?

Fossil fuels are the world’s most widely-used energy resource, and as such they are an essential ingredient in contemporary life. Without fossil fuels there would almost certainly be no cars, aeroplanes, plastics, domestic electricity supplies, or many other conveniences that are taken for granted in the developed world. But fossil fuels are non-renewable. If supplies were to run out, we would face a grave energy crisis. For this reason, and also because of their environmental impact, fossil fuels are a topic of hot political debate.

Coal, oil and natural gas are all fossil fuels. Formed by natural geological processes, these substances have been deposited deep beneath the surface of the earth. Their chemical composition is such that when they burn, they release heat and energy, which can be harnessed for a tremendous variety of applications. For more than a century the coal-mining industry, the oil and petrochemical industries and the offshore gas industry have been able to meet the world’s energy requirements by extracting, processing and delivering fossil fuels.

The Scientific Bit: Formation and Composition

Essentially, deposits of fossil fuels are the residue of organisms that died hundreds of millions of years ago. Across parts of continents, decomposing vegetation amassed in layers across forest floors, and over time these layers were buried deeper and deeper beneath the earth’s crust. As the mass of rock above them grew heavier, the decayed vegetation was subjected to extreme forces of pressure and heat. These forces brought about a series of chemical changes that gradually, over many millions of years, transformed the buried organic matter into a hydrocarbon that has a very high ratio of carbon to hydrogen: coal. Today coal is mined in many parts of the world, particularly China and the US.

A similar process happened in the marine environment, where large quantities of dead plankton accumulated on the sea bed and were subsequently buried by layer after layer of sediment. Over time, the weight of the sediment became so great that it created pressure and heat that eventually converted the decomposed plankton into liquid and gaseous hydrocarbons – petroleum and natural gas. In the millions of years since these layers of plankton-laden mud were compressed, geographical shifts in oceans and continents have occurred so that oilfields and natural gas fields are now situated inland as well as offshore. Most of the world’s oil comes from the Middle East, whilst other major oil-producing countries include the US and Russia. Natural gas is found alongside oil, and also occurs in separate natural gas fields scattered all around the world.

The Combustion Process and the Greenhouse Effect

The fact that fossil fuels are hydrocarbons is very significant. Hydrocarbons are chains of the two elements hydrogen (H) and carbon (C). When hydrocarbons are burned in an atmosphere containing oxygen (O), they react with the oxygen to produce carbon dioxide (CO2) and water (H2O). Because hydrocarbons and oxygen are both much less stable than CO2 and water, a great deal of energy – in the form of light and heat – is released during the combustion process.

Carbon dioxide is a ‘greenhouse gas’, reckoned to be a major contributor to climate change. Other emissions produced when fossil fuels are burnt include nitrogen and sulphur, which combine with water vapour to give us ‘acid rain’. The combustion of some fossil fuels also releases particulates (tiny solid particles) which have a detrimental effect on air quality.

A Non-Renewable Resource

Modern industrialised society is hungry for energy, and most of this energy is still derived from fossil fuels. Almost 80 per cent of the UK’s electricity is produced by coal-fired and gas-fuelled power stations. Globally, oil refineries produce vast quantities of petrol and diesel in response to the massive popularity of motor vehicles, as well as the highly-refined aviation fuel required by the airlines and the petroleum products needed by the plastics industry. But fossil fuels are a non-renewable resource.

If consumption continues at this rate, not only do we risk escalating global warming and other undesirable environmental consequences, but according to some scientists our supplies, particularly of oil, are already in danger of running out. World leaders are currently addressing the need to reduce dependence on fossil fuels, in an effort to bring emissions down to less damaging levels and prevent reserves from being exhausted prematurely.

Our word ‘fossil’ comes from the Latin ‘fossilis’, meaning something that has been dug up. For a long time we have satisfied our energy needs by taking coal, oil and gas out of the earth. However, it is now recognised that we must move towards renewable energy sources – for example solar power and wind power – and in order to protect our environment and preserve supplies of these invaluable resources, created by Earth herself over millions of years: fossil fuels.