Fossil fuels are coal, oil and natural gas. They formed underground over millions of years from the remains of ancient plants and animals, changed by heat and pressure. People burn them for electricity, heat and transport. They are non-renewable, and burning them releases carbon dioxide, a greenhouse gas that warms the planet.
fossil fuels quick facts
- Coal formed from plants that grew in swampy forests hundreds of millions of years ago.
- Oil formed from tiny sea plants and animals, such as diatoms.
- A 42-gallon barrel of crude oil gives about 45 gallons of products in US refineries.
- Gas companies add a smelly chemical called mercaptan so leaks can be noticed.
- About 60% of US electricity comes from burning fossil fuels.
What are fossil fuels?
Fossil fuels are fuels that formed underground from the remains of plants and animals that lived millions of years ago. The three main ones are coal, oil and natural gas.
They are called fossil fuels because, like fossils, they come from ancient living things. Those plants and animals took in energy that came, in the end, from the Sun. When we burn fossil fuels, we release that stored energy as heat.
Fossil fuels are non-renewable. They took millions of years to form, so once we have used them, they will not come back in any time that matters to people.
Fossil fuels in history
People have burned coal for a very long time. But fossil fuels really took over in the 1700s and 1800s, during the Industrial Revolution.
Coal fed the steam engines that drove factories, trains and ships. Later, oil and petrol powered cars and aeroplanes, and gas lit streets and heated homes.
Those changes made travel faster and goods cheaper. They also began the rise in carbon dioxide that scientists measure in the air today.
Who discovered fossil fuels?
Nobody did. There is no name to learn here, and that is the interesting part.
Coal was never hidden. Where a seam reaches the surface you can pick lumps of it off the ground, and people did that long before anyone thought to write it down. In North America the explorer Louis Joliet marked coal on his map of the Illinois River in 1673. Organised mining near Richmond, Virginia began in 1748.
Oil was not hidden either. It seeps up through cracks in the rock, and people had been scooping it off pools and streams for thousands of years. They used it to waterproof boats and to treat sore skin.
How coal forms, in order
- First Plants grow in swampy forests, hundreds of millions of years ago.
- Then The plants die and pile up in the swamp.
- Next Layers of dirt and rock cover the pile.
- Under pressure The weight of those layers presses down on the plant remains.
- Deep down Heat deep underground slowly changes what is left.
- At last The remains become coal, holding energy the plants stored from sunlight.
So the date everyone quotes is not a discovery at all. On 27 August 1859, Edwin Drake finished drilling 69 feet into the ground near Titusville, Pennsylvania, and hit oil. What was new was the drilling. Before that you could only take what leaked out by itself.
That is the difference worth holding on to. Finding something and working out how to get a lot of it are two separate problems. Fossil fuels were found over and over, by people whose names nobody wrote down. The industry started when somebody drilled a hole.
How coal formed
Coal is a black or brownish-black rock that burns. It is packed with carbon.
It began as plants that grew in swampy forests hundreds of millions of years ago. When the plants died, they piled up in the swamps. Over millions of years, layers of dirt and rock covered them.
The weight of those layers pressed down on the plant remains, and the heat deep underground slowly changed them into coal. So every lump of coal holds energy that plants stored from sunlight long, long ago.
Four kinds of coal
Not all coal is the same. Scientists sort it into four kinds, called ranks, depending on how much carbon it contains.
| Rank | Carbon | Share of US coal mined in 2022 |
|---|---|---|
| Anthracite | 86% to 97% | less than 1% |
| Bituminous | 45% to 86% | about 46% |
| Subbituminous | 35% to 45% | about 46% |
| Lignite | 25% to 35% | about 8% |
Anthracite has the most carbon and gives off the most heat when it burns, but very little of it is mined. Bituminous and subbituminous coal together make up more than nine tenths of the coal dug up in the United States. Lignite has the least carbon and the least energy.
Bituminous coal is burned to make electricity. It is also used to make coke, a fuel needed for making iron and steel.
How oil formed
Crude oil, also called petroleum, is a mixture of chemicals called hydrocarbons. As the name suggests, they are made of hydrogen and carbon. You can find out more about the first of these in our hydrogen facts.
Oil formed from tiny plants and animals, such as diatoms, that lived in the sea millions of years ago. When they died, they were buried under layers of sand, silt and rock. Heat and pressure slowly turned them into oil.
Fossil fuel words
- Hydrocarbon — a chemical made of hydrogen and carbon
- Refinery — where crude oil is separated into different products
- Petroleum — another name for crude oil
- Tar sands — sand near the surface with oil mixed into it
- Diatoms — the tiny sea plants and animals that oil formed from
- Coke — a fuel made from coal and needed for making iron and steel
Oil is not found in big underground lakes. It sits in tiny spaces inside rocks, a bit like water soaked into a sponge. Some is found near the surface, mixed into sand, in what are called tar sands or oil sands.
From crude oil to petrol
Crude oil is not much use straight out of the ground. First it goes to a refinery, where it is separated into different products.
These include petrol, which Americans call gasoline, as well as diesel, heating oil and jet fuel.
Here is a strange fact. In American refineries, a 42-gallon barrel of crude oil gives about 45 gallons of products. The products take up more space than the crude oil they came from.
Chemicals from oil are also used to make plastics and many other everyday things.
Natural gas
Natural gas is mostly methane. A methane molecule is made of one carbon atom joined to four hydrogen atoms.
It formed in the same way as coal and oil, from the remains of plants and animals buried under thick layers of earth and rock, then changed by heat and pressure.
To find it, geologists send sound waves into the ground and study the echoes that come back. These are called seismic surveys.
Some gas is locked tightly inside hard rock. To release it, companies pump liquid into the rock at high pressure to crack it open. This is called hydraulic fracturing, or fracking.
Fossil fuels by numbers
- About 60 per cent — the share of US electricity that comes from burning fossil fuels
- More than 94 per cent — the share of US transport fuel that comes from oil
- 42 gallons — the size of a barrel of crude oil
- About 45 gallons — what one barrel of crude oil makes in US refineries
- Four — the number of ranks that scientists sort coal into
- One carbon and four hydrogen atoms — what a methane molecule is made of
Natural gas has no smell of its own. Gas companies add a chemical called mercaptan, which smells very unpleasant, so that people notice straight away if there is a leak.
People use natural gas to heat homes, to cook and to make electricity. It is also used to make materials and chemicals.
How we use fossil fuels
Fossil fuels power a huge part of modern life. In the United States, about 60% of electricity comes from burning fossil fuels.
They also keep us moving. More than 94% of the fuel used for transport in the United States comes from oil, in cars, lorries, ships and planes.
Factories burn fossil fuels to make things, and many homes are heated with gas or oil.
The problem with fossil fuels
When fossil fuels burn, the carbon inside them joins with oxygen from the air to make carbon dioxide. Carbon dioxide is a greenhouse gas, which means it traps heat in the atmosphere.
Think of a greenhouse in a garden. Sunlight passes through the glass and warms the plants inside, and the glass stops much of that heat from escaping. Greenhouse gases work in a similar way for the whole Earth. A little keeps the planet warm enough for life. Too much makes it warmer than it should be.
In the United States, burning fossil fuels for electricity, heat and transport is the largest source of greenhouse gases from human activity. Transport is the biggest single source.
Extra greenhouse gases are making our planet warmer and changing its climate. You can read more about that in our global warming facts for kids.
Getting fossil fuels out of the ground can harm the land and water too. Mines scar the landscape, and oil and gas can leak or spill.
Why are they still used?
If fossil fuels cause problems, why do we still use them? Part of the answer is that they pack a lot of energy into a small space.
They are also easy to store and move. A power station can burn coal or gas whenever electricity is needed, day or night, whatever the weather.
Changing to other kinds of energy takes time, money and new machines, from power stations to cars. That is why the change is happening step by step. More and more cars now run on electricity, and more of that electricity comes from the wind and the Sun.
Advantages and disadvantages
Here is the whole argument in one table. Both columns are true at the same time, which is exactly why the question is hard.
| Advantages | Disadvantages |
|---|---|
| A small amount holds a lot of energy, so a tank of fuel takes a lorry a long way | Burning them releases carbon dioxide, which warms the planet |
| They work at night, in still air and in any weather | They also release soot and gases that make people ill |
| Power stations, pipes, ships and engines are already built for them | There is a fixed amount underground and it is not being replaced |
| In many places they are cheap to dig up or pump out | Mining and oil spills damage land, rivers and sea |
| They can be stored for years and moved anywhere | Prices swing hard, because a few countries hold most of the supply |
Notice that the advantages are all about how convenient they are. The disadvantages are all about what they cost, in health, in damage and in time we do not get back.
Cleaner choices
Renewable energy comes from sources that do not run out, such as sunlight, wind and flowing water.
Fossil fuels: fact or myth?
- The energy stored in fossil fuels came, in the end, from the Sun.
- Solar panels and wind turbines give off carbon dioxide while they are working.
- A coal or gas power station can make electricity at any time, day or night, whatever the weather.
- All coal holds the same amount of energy.
- When hydrogen is used in a fuel cell, the only thing that comes out is water.
- Fracking means digging a very deep hole to reach gas.
Solar panels turn sunlight into electricity. Wind turbines use the wind, and hydroelectric dams use falling water. None of them burns fuel as they work, so they do not give off smoke or carbon dioxide while they run.
Hydrogen can be used as a fuel too. When it is used in a fuel cell, the only thing that comes out is water.
You can help as well, by switching off lights, walking or cycling short distances and not wasting energy at home.
Three things people get wrong
Fossil fuels are not made from dinosaurs. Coal formed mainly from ancient swamp plants, and oil from tiny sea plants and animals.
Oil is not found in underground lakes. It fills tiny spaces inside rock, like water in a sponge.
Natural gas does not smell by itself. Gas companies add a smelly chemical, mercaptan, so that leaks are easy to notice.
Did you know? Oil is not stored in underground lakes. It fills tiny spaces inside rocks, a bit like water in a sponge.
Try it
Make a list of everything in your home that uses electricity, gas or petrol. Then think about which ones you could use a little less.
Knowledge check
What are the three main fossil fuels?
Show answer
Coal, oil and natural gas.
Which kind of coal has the most carbon?
Show answer
Anthracite, with 86% to 97% carbon.
Frequently asked questions
What are fossil fuels?
Fossil fuels are coal, oil and natural gas. They formed over millions of years from the remains of ancient plants and animals, buried and changed by heat and pressure.
How is coal formed?
Coal formed from plants that grew in swampy forests hundreds of millions of years ago. Layers of dirt and rock covered them, and pressure and heat slowly turned them into coal.
How is oil formed?
Oil formed from tiny plants and animals, such as diatoms, that lived in ancient seas. They were buried under sand, silt and rock, and heat and pressure turned them into oil.
Why are fossil fuels bad for the environment?
Burning fossil fuels releases carbon dioxide, a greenhouse gas that traps heat and warms the planet. Mining and drilling can also harm land and water through spills and leaks.
Why are fossil fuels non-renewable?
Fossil fuels are non-renewable because they take millions of years to form. Once they are used up, they cannot be replaced in any time that matters to people.
What can we use instead of fossil fuels?
Instead of fossil fuels we can use renewable energy from sunlight, wind and flowing water. Hydrogen can also be used as a fuel, producing only water in a fuel cell.
Sources
- US Energy Information Administration: coal explained — what coal is, how it formed and the four ranks of coal
- US Energy Information Administration: oil and petroleum products explained — how oil formed, where it is found, refining and the barrel of oil
- US Energy Information Administration: natural gas explained — methane, how gas formed, seismic surveys, fracking and mercaptan
- US Environmental Protection Agency: sources of greenhouse gas emissions — fossil fuels and US greenhouse gas emissions, electricity and transport
- US Energy Information Administration: coal timeline — Joliet’s 1673 map and the start of organised mining in 1748.
- US Energy Information Administration: Edwin Drake — the 1859 well near Titusville and why it counts as the start of the oil industry.
Fossil Fuels Final Challenge
- Why are fossil fuels called non-renewable?
- When did fossil fuels really take over as the world's main energy source?
- Where is oil actually found underground?
- How do geologists look for natural gas?
- Why is mercaptan added to natural gas?
- What happens to the carbon in fossil fuels when they burn?
- In the United States, what is the biggest single source of greenhouse gases from human activity?
- What does a greenhouse gas do?
- Which of these is a renewable source of energy?
- Besides fuel, what else is made from chemicals in oil?
