Fossil fuels such as coal, oil, and natural gas were formed from the remains of ancient plants and animals over millions of years. Coal formed from decayed plant matter that was subjected to heat and pressure deep underground, while oil and natural gas formed from the remains of tiny sea creatures buried beneath ocean sediments. These fossil fuels are non-renewable energy resources that are extracted through mining and drilling, and are important fuels used worldwide to power vehicles, heat homes, and generate electricity. Major oil spills such as the Exxon Valdez and Deepwater Horizon disasters have caused environmental and economic damage.