2.1 Fossil Fuel Formation

📖 Main Content

What Are Fossil Fuels?

Fossil fuels are natural fuels found underground. They formed over hundreds of millions of years from the remains of dead plants and animals. Because they took so incredibly long to form — far longer than a human lifetime, or even the entire history of human civilisation — we call them non-renewable resources. This means once we use them up, they are gone forever and cannot be replaced in any practical timeframe.

The three main fossil fuels are:

• Coal
• Oil (also called crude oil or petroleum)
• Natural gas

🔶 Formation of Coal

Coal formed mainly from the remains of ancient plants — particularly trees, ferns, and other vegetation that grew in vast swampy forests during a period called the Carboniferous Period, roughly 300–360 million years ago.

Here is how it happened, step by step:

1. Plants died and fell into swampy water. Because the swamps were waterlogged and lacked oxygen, the dead plant material did not fully rot away as it normally would on land.

2. Over time, layers of dead plant material built up on the swamp floor. This compressed, partially decayed plant material is called peat. Peat is the very first stage of coal formation — it is soft, spongy, and dark brown.

3. More layers of sediment (mud, sand, and rock) were deposited on top of the peat over millions of years. This added enormous pressure from above, and the heat deep underground also increased.

4. The pressure and heat slowly squeezed out water and gases from the peat, compacting it more and more. Over millions of years, the peat was gradually transformed:

   • First into lignite (also called brown coal — soft and low-quality)
   • Then into bituminous coal (darker and harder)
   • And finally, under the most extreme pressure, into anthracite (the hardest, highest-quality coal with the most carbon)

5. The result is a solid, black or dark-brown rock rich in carbon — what we call coal.