Fossil fuels
Coal, oil, and natural gas are the three principle fossil fuels found on earth. All three of these products come from organic matter that is millions of years old. Through a combination of heat and pressure, they became the fossil fuels we know today.
In most cases, crude oil and natural gas came from prehistoric zooplankton and algae. Coal, however, is derived from plants that lived 100 to 400 million years ago. Back then, most of the earth was covered in swamps, which were ideal for plant growth.
When plants die, they decay and release energy. However, if water and mud cover dead plant matter they can prevent normal oxidation and biodegradation processes. Over time, the water and mud compacted ancient plant matter, and leaving behind energy-rich hydrocarbons which eventually became coal.
