Fossil fuels come from the remains of fossilized organic material that has been transformed by the Earth’s heat and pressure over time. Coal, oil and natural gas – all types of fossil fuels – are nonrenewable resources because their formation takes millions of years and the supply of such fuels is finite. Although a majority of the world’s energy is produced by these fuels, there have been efforts to cut down on their use because of environmental concerns and rising prices. {Renewable energy} sources are alternatives to fossil fuels.