Fossil fuel

A fossil fuel is a fuel that comes from reserves created a very long time ago.

Formation of fossil fuels

• Uranium 235 (²³⁵U), used in nuclear reactors, was formed during the supernovas that preceded the formation of the Solar System;
• petroleum, natural gas and coal are the result of the slow transformation of residue from organisms that died millions of years ago (plankton, plants).

Fossil fuels and hydrocarbons exist in finite quantities. Reserves of these fuels are exhausted as they are used, which is not the case for renewable energy.