are rocks created through the accumulation of sediments from water and the earth.
Fossil fuels such as coal, oil shale and petroleum are accumulations of organic tissue that has been preserved for millions of years. They can be found in what is called "organic-rich" sedimentary rocks.
Layers of sedimentary rock containing fossils.
- See also: Traditional energy resources
Sediments from sedimentary rock form layers at the bottom of seas and valleys, and new layers increase pressure on the older ones. The combination of pressure and temperature transforms organic matter into fossil fuels, which are the most common traditional energy resources used to make gasoline and other forms of energy. When sediments are transformed into peat, and when peat is buried under more sediment, coal can be formed, another traditional source of energy. With more pressure and time, natural gas can also form from organic matter.