Exactly what is a fossil fuel? A fossil fuel is coal, oil or natural gas. They’re called fossil fuels because of the way and the time they developed. A fossil fuel started developing before the time of the dinosaurs, which is why “fossil” is included in the name. This period is called the Carboniferous Period because of the carbon contained in fossil fuels. Fossil fuels were formed when animals, trees and plants died and then sank to the bottom of swampy areas and oceans. These layers of rotten matter formed what is called peat, a spongy organic matter. After hundreds of years, the peat was covered with layers of rock, clay and sand, which turned into sedimentary rock. Eventually, more layers of rock accumulated, causing the weight to squeeze down the peat. After millions of years of this pressure, fossil fuel was formed. The pre-curser to coal is peat, which is found in many parts of the country. Oil was formed by Diatoms, which are tiny sea creatures. The carbon in their bodies turned to oil under the earth’s pressure and heat. Natural gas, or methane, is found near petroleum stores. That’s why they’re called fossil fuels!