Natural gas is one of the world's most important fossil fuels. The denotation of "fossil fuel" comes from the belief that most scientists share, that natural gas and other "fossil fuels" were formed from the remains of tiny sea animals and plants that perished 200-400 million years ago. Scientists believe that when these tiny organisms died, they sank to the bottom of the ocean, where over many years, the pressure created by the ever-thickening layers of ocean floor combined with the earth's heat to change the molecular structure of the organic remains into deposits of petroleum and natural gas. Natural gas only occurs in the areas of the earth where this built up pressure and volcanic heat combine to produce the necessary chemical reaction for production. Geologists are able to locate natural gas deposits by studying the types of rock and formations that usually occur where gas is present. Raw natural gas is a mixture of gases whose main ingredient, methane, is a natural occurring compound formed when plant and animal matter decays. It is odorless, colorless, and tasteless, so companies like Triple Diamond Energy Corp add a chemical with a sulfuric smell like rotten eggs so that leaks can be detected quickly, otherwise the volatile fuel leaking could rapidly lead to dangerous situations within the home or industrial environments.