The secret to fossil fuels’ ability to produce energy is that they contain a large amount of carbon. This carbon is left over from living matter primarily plants that lived millions of years ago. Oil and natural gas are usually the result of lots of biological matter that settles to the seafloor, where the hydrocarbons (molecules of hydrogen and carbon), including methane gas, become trapped in rocks. Petroleum sources are usually small pockets of liquid or gas trapped within rock layers deep underground (often under the seafloor). Extracted crude oil is refined and used to manufacture gasoline (used in transportation) and petrochemicals (used in the production of plastics, pharmaceuticals, and cleaning products).Oil companies pump liquid oil out of the ground by using drilling rugs and wells that access the pockets of oil resources. The oil fills the rock layers the way water fills a sponge spreading throughout open spaces instead of existing as a giant pool of liquid.Transforming crude oil into petrochemicals releases toxins into the atmosphere that are dangerous for human and ecosystem health. Although oil doesn’t produce the same amount of CO2 that coal burning does, it still contributes greenhouse gases to the atmosphere and increases global warming. Large oil spills sometimes occur during drilling, transport, and use, which of course affect the surrounding environment. But these spills aren’t the only risk.