Fossil fuels - Oil, Coal, Gas Earth science for schools by Moorland School


Crude oil, natural gas and coal are fossil fuels. Fossil fuels are very precious resources because they are non-renewable (once they're used, that's it!). We can also make lots of organic chemicals from them, needed to make products such as paints, detergents, polymers (including plastics), cosmetics and some medicines.

Fossil fuels were formed from the fossillized remains of dead plants and animals that once lived millions of years ago. Oil and natural gas are the products of the deep burial and decomposition of dead plants and animals. Heat and pressure, in the absence of oxygen, transform the decomposed material into tiny pockets of gas and crude oil. The oil and gas then migrates through the pores in the rocks to eventually collect in reservoirs.

Coal comes mainly from dead plants which have been buried and compacted beneath sediments. Most coal originated as peat in ancient swamps created many millions of years ago.

What is crude oil?

Crude oil is a complex mixture of hydrocarbons with small amounts of other chemicals such as sulphur. The crude oil is useless as a mixture and must be sent to an oil refinery to be separated. Crude oils from different parts of the world, or even from different depths in the same oilfield, contain different mixtures of hydrocarbons and other compounds. This is why they vary from light coloured volatile liquids to thick, dark oils.

What is natural gas?

A methane molecule Natural gas is a mixture of hydrocarbons with small molecules. These molecules are made of atoms of carbon and hydrogen. For example, natural gas used in the home is mainly methane, CH 4.

What is a hydrocarbon?

Hydrocarbons only contain hydrogen and carbon atoms. There are two main chemical families of hydrocarbons - the alkanes and the alkenes. Thousands of synthetic products can be manufactured from hydrocarbons with many different properties. Click here for some more info on polymers and plastics.


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