Fossil Fuels



Hydrocarbons - why are they so important?


Almost all  living things contain compounds of hydrogen and carbon. We call these compounds hydrocarbons. The major sources of hydrocarbons are CRUDE OIL, Natural gas and Coal- the fossil fuel family.  The hydrocarbons in crude oil are not only important fuels, they are also the starting point of many other new chemicals products, for examples PLASTICS. 

Fossil Fuels - Coal, Crude Oil and Natural Gas

Out of these three fossil fuels, coal is the odd one out, as it not a true hydrocarbon.  Nevertheless it does contain hydrogen and carbon along with other types of atoms, for example oxygen, in some of its structure.

How were they formed?

Fossil fuels were formed from dead plants and animals.  All the energy that is stored in fossil fuels, as chemical energy, originally came from the Sun.


About 300 million years ago, the Earth surface was overrun with plant life. Plants died and fell into swampy water and were covered by mud, which stopped them from rotting.

Precambrian Forest

As the mud piled up, it compressed the plants.

After millions of years of pressure the mud became rock and the plants turned into coal.  

As coal is found deep underground, to reach it, miners dig deep shafts and tunnels.  It is estimated that there is enough coal to last us 300 yearsFossils of plants are sometimes found in layers of coal.


Crude Oil and Natural Gas

Crude oil and natural gas were formed under similar circumstances as coal. Many parts of the Earth were under water which contained many animals. These animals died and were immediately covered by sediments on the seabed. The dead sea creatures were buried under many layers of mud and sand. They did not decay.

Precambrian Sea

After many millions of years of pressure and heat (90°C to 120°C) this process turned the mud and sand into rock and dead animals into  crude oil and natural gas. These two are found very deep underground between layers of impermeable rock. These rocks prevents the oil from seeping through.  

Natural gas is found in pockets on top of the crude oil under a layer of non-porous rock.  The gas is a mixture of compounds made up of hydrogen and carbon only. These are small molecules with a low molecular mass.

This gas is used on a large scale as a fuel. It is also used for the manufacture of more complex organic substances.


Oil is usually found approximately 2 to 3 miles beneath the ground.  It is trapped in rocks as shown on the diagram opposite.  To get at the oil, a hole is bored, either in the ground or sea bed, using giant drills.  The drill is hung from a giant metal frame, like the one on the left or from a  drilling platform in the case of over water, like the one on the right.


Once the oil is discovered,  it is usually under pressure and comes up by it self.  The next step is that the hole is lined with steel pipes.  Then the oil is pumped through them.  It is carried ashore, to an oil refinery, in pipes that run along the land or sea bed.

Rig Pump

Coal, natural gas and crude oil are fossil fuels. They are an extremely valuable resource and must be used carefully and efficiently because we have a very limited supply of them and the fact that they are non-renewable resources.


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