Fossil fuels are the fuels formed by natural processes such as the decomposition of dead and buried organisms.
Fossil fuels are buried flammable geologic deposits of organic substances such as dead plants and animals that got deposited under several thousand feet of silt.
These deposits decayed with the passage of time and got converted to natural gas, coal, and petroleum due to the extreme heat and pressure inside the earth’s crust.
They are also known as non-renewable sources of energy as it takes a very long time for them to replenish.