Formation of fossil fuels

Crude oil, coal and gas are fossil fuels. They were formed over millions of years, from the remains of dead organisms:

  • coal was formed from dead trees and other plant material
  • crude oil and gas were formed from dead marine organisms
Pile of coal
Coal is a solid fossil fuel

Fossil fuels are non-renewable. They took a very long time to form and we are using them up faster than they can be replaced - once they have all been used up, they cannot be replaced. Fossil fuels are also finite resources. They are no longer being made or are being made extremely slowly.

How crude oil and natural gas were formed

Millions of years ago, huge numbers of microscopic animals and plants - plankton - died and fell to the bottom of the sea. Their remains were covered by mud.

As the mud sediment was buried by more sediment, it started to change into rock as the temperature and pressure increased. The plant and animal remains were altered chemically by this process, and slowly changed into crude oil and natural gas. The slideshow describes what happened and how we get oil from the ground today:

1 of 3: Plants and animals die and then sink to the sea bed. This is 300 to 400 million years ago.

The oil moved upwards through the spaces in permeable rock. It became trapped if it reached impermeable rock. Oil companies can drill down through the impermeable rocks to get it out. They are then able to turn it into products we can use, such as petrol and diesel.