Oil & Natural Gas
The three main forms of fossil fuels — coal, oil and natural gas — formed hundreds of millions of years before the time of dinosaurs, hence the name fossil fuels.
As trees and plants died, they sank to the bottom of swamps or oceans. They formed layers of a spongy material called peat. During the course of several hundred years, the peat was covered by sand and clay and other minerals, which turned into a type of rock called sedimentary.
More rock piled on top of more rock. It began to press down on the peat. The peat kept getting squeezed until the water came out of it, and it eventually, millions of years later, it became coal, oil or petroleum, and natural gas.