Fossil fuels are important to our everyday lives and we use them to meet most of our energy needs. The reason they are so widely used is that they are convenient and effective. At the moment they are plentiful and relative to other forms of energy, inexpensive. They are called fossil fuels because they are formed from the remains of plants and animals. Most of the World’s supply of these materials formed during the Carboniferous Period, 286 to 360 million years ago.
Coal was the first of the fossil fuels to be widely used. Kilogram for kilogram, coal releases much more energy than wood and it made the Industrial Revolution possible. During the Carboniferous Period, in the Earth’s tropical regions, vast forests of fern-like trees and other leafy plants were growing.
As they died, their remains formed huge deposits of peat. Over millions of years, in certain places, the peat become covered in sediments from rivers and was buried. As the sediments built up, the peat was buried more deeply and gradually it became coal whilst the sediments in between the layers of peat turned into rock.
At the same time that the swampy forests were alive, the seas were teeming with algae and other microscopic sea creatures. As they died, their remains sank to the bottom of the oceans and mixed with the sediments on the sea floor. As the mixture of sediments and sea creatures built up over the course of millions of years, the sediments turned to rock and the remains of the creatures became oil.
Many people imagine oil fields to be like a large underground lake. That is not the case, the oil is in the pores between the particles of sedimentary rocks. Oil is less dense than rock so it tends to move upwards. When it reaches a rock layer that is both impervious and non-porous, it can go no further and becomes trapped. Where oil is trapped in this way, that is when we say there is an oil field. Because it is buried deeply, it is under pressure and when we drill down to it, the oil comes rushing to the surface. Oil is also referred to as petroleum.
3. Natural Gas
Natural gas is formed at the same time as both oil and coal, the main chemical in it is called methane which is highly flammable. Like oil, it moves upwards, towards the surface of the Earth and can be trapped in the same way as oil.
Although it is associated with coal as well, it is not possible to extract it so all of the natural gas we use for cooking, heating and generating electricity comes from oil.
Disadvantages of Burning Fossil Fuels
Burning fossil fuels creates pollution. They produce a lot of carbon dioxide which contributes to the greenhouse effect that is causing global warming.
They also produce sulphur dioxide, a gas that contributes to the acid rain problem but there are ways of reducing the amount of sulphur dioxide produced. At power stations, a process called ‘flue gas desulphurisation‘ is used which removes the sulphur dioxide from the waste gases.
For fuel for cars, lorries etc., sulphur is removed during the refining process. If there is no sulphur in the fuel, sulphur dioxide cannot be formed when the fuel is burnt.