成人快手

Key facts

Gas, coal and oil are聽fossil fuels.

Using them is unsustainable because they emit carbon dioxide and other greenhouse gases that are causing global heating and climate change.

Fossil fuels are the remains of creatures and plants that lived millions of years ago. That鈥檚 the fossil bit. All of these creatures and plants contain carbon, which gives off energy when it鈥檚 burned 鈥 that鈥檚 why they are fuels.

Fossil fuels are non renewable. They take millions of years to form, so once they have all been used up, they cannot be replaced.

An oil refinery at Sarnia, Ontario, Canada.
Image caption,
An oil refinery at Sarnia, Ontario, Canada.

Fossil fuels and their impact

Find out how fossil fuels can be used to generate electricity.

How fossil fuels are formed

How oil and gas are formed

Image gallerySkip image gallerySlide 1 of 3, Slideshow page one: Dead creatures and plantlife build up on the sea bed,
  1. Both oil and gas come from layers of dead marine organisms, such as tiny animals and plant life, like plankton.
  2. When they died, their bodies fell to the bottom of the sea. Over millions of years, layers of mud and rock built up over them which put them under massive pressure.
  3. This, together with the heat from the earth鈥檚 mantle, changed them into oil and gas.

How coal is formed

Image caption,
Coal is a solid fossil fuel formed over millions of years from the remains of ancient trees
  1. Coal comes from dead trees from ancient forests.
  2. Over time these become buried under layers of soil and other material.
  3. This build up of material creates huge pressure.
  4. Over millions of years this pressure combined with geothermal heat compresses the dead trees into coal.
Image caption,
Coal is a solid fossil fuel formed over millions of years from the remains of ancient trees

Extracting fossil fuels

Fossils fuels are still important to Scotland. We don鈥檛 mine coal anymore, but we still have over 100 oil and gas rigs out in the North Sea and they employ a lot of people

Gas and oil drilling

Image caption,
Scotland's oil and gas reserves are located under the North Sea and are accessed using drilling rigs.

Oil and gas can be found stored in reservoirs deep underground or beneath the sea. Drilling machines are used to reach the fuels which can then be transported to the surface through pipes.

Scotland's oil and gas come from reserves under the North Sea which are reached using surface drilling rigs.

Extracting oil and gas can cause pollution to the sea and seabed around where drilling takes place. Oil spills can pollute wider areas and harm wildlife and habitats over periods of years.

Image caption,
Scotland's oil and gas reserves are located under the North Sea and are accessed using drilling rigs.

Coal mining

Image caption,
Both open cast and underground mining result in pollution and environmental damage

Coal consists of carbon with organic and inorganic compounds. It is mined from seams of coal found between layers of rock in the ground.

Where the coal is deep below the surface,underground mining or deep mining methods are used. This involved digging deep shafts and tunnels to allow miners and machinery to reach the coal seams.

Where the coal is at a shallow depth, open cast mining or surface mining is used. This involves using machinery or explosives to remove the layers of soil and rock above the coal seam.

Both types of mining cause air, water and soil pollution which can damage human health and the local environment and waterways.

Image caption,
Both open cast and underground mining result in pollution and environmental damage

Oil refining

Crude oil is made up a mixture of different hydrocarbons - substances made from carbon and hydrogen only. These hydrocarbons have different properties and can be used for different purposes.

Fractional distillation is used to separate crude oil into simpler, more useful mixtures. This method can be used because the different hydrocarbons have different boiling points.

Crude oil is split into different products by the process of fractional distillation.
Figure caption,
Crude oil can be split into different products through the process of fractional distillation.

During the fractional distillation of crude oil:

  1. Heated crude oil enters a tall fractionating column, which is hot at the bottom and gets cooler towards the top.
  2. Vapours from the oil rise through the column.
  3. Vapours condense into liquids when they become cool enough.
  4. Different liquids are let out of the column at different heights.
  5. The smallest hydrocarbon molecules do not condense, but leave the column as gases.
  6. Long hydrocarbon molecules have high boiling points and so they do not evaporate into gases. They leave the column as hot liquid bitumen.

The different, useful mixtures are called fractions. This is because they are only part of the original crude oil.

How fossil fuels are used

Fossil fuels as energy sources

The main use of fossil fuels is burning them as fuel. When they burn the chemical energy stored in them is transferred into heat energy.

That heat energy can then be used in a number of ways:

  • Gas is burned in our homes to provide central heating and to cook food.
  • Petrol and diesel from oil are burned to move pistons in engines to make cars and other vehicles move.
  • Coal, gas and oil can all be burned in power stations to generate electricity.

Generating electricity

Diagram showing how coal and burned to generate electricity

Around the world, coal is burned for heating and also used in power stations. In China, more than half the electricity generated is produced by burning coal

Making plastics

While plastics can be made from plants, most of the plastics we use every day are made from crude oil.

When crude oil is distilled, one of the fractions produced is a chemical called naphtha.

The naphtha then goes through a process called cracking, which breaks it down into small molecules called monomers. These can be joined together in chains called polymers. For example the monomer ethene is joined in chains to make the plastic polyethene or polythene.

Ethene monomers join in chains to form polyethene.
Figure caption,
Naphtha from crude oil is cracked to produce monomers like ethene. Ethene is the joined in chains to make the plastic polyethene.

Making steel

Coal is used to turn iron ore into steel.

The coal acts as a fuel that heats a blast furnace. As the coal burns, it produces carbon monoxide gas. This releases oxygen from the iron ore, leaving iron metal. Limestone and other materials are added to remove impurities.

It its pure form, iron is a relatively soft metal. Adding small amounts of carbon to iron to produce steel creates a much stronger alloy.

Sustainability of fossil fuels

Wind turbines and lignite coal mines at Niederzier, Germany
Image caption,
Wind turbines and lignite coal mines at Niederzier, Germany

To develop a sustainable future you need to think about meeting today's needs and protecting the聽environment听补苍诲听resources聽for the future.

Burning fossil fuels is not sustainable. It creates carbon dioxide which traps energy from the Sun in the Earth's atmosphere. This is a major cause of global heating.

Other gases released cause pollution which is bad for our health and for other living things.

Extracting fossil fuels can cause local environmental damage. Oil leaks and can pollute ground and water and harm wildlife.

Advantages and disadvantages of using fossil fuels

Advantages

  • They generate large amounts of energy quite cheaply.
  • They can be easy to use. Burning coal or gas only needs a flame source and oxygen supply.
  • They are portable - Oil and gas can be transported through pipelines. Petrol and other fuels can be stored in tanks and easily transferred to cars and other vehicles.

Disadvantages

  • Fossil fuels are bad for our planet. When fossil fuels are burned, they release carbon dioxide 鈥 which is one of the that cause global heating.
  • Burning fossil fuels also causes a lot of pollution. It can affect the quality of the air we breathe and make people ill. It can even kill people.
  • Mining can create ugly scars on the landscape and destroy wildlife habitats.
  • Oil spills聽can cause environmental damage harming aquatic wildlife.
  • Oil is mainly produced outside the UK, so prices are set by other countries.
  • Fossil fuels are non-renewable. This means there鈥檚 only so much of them and once we鈥檝e run out, that鈥檚 it, there's no more.

Test your knowledge

More on Energy sources and sustainability

Find out more by working through a topic