Fossil fuels are carbon-based energy sources like coal, oil and natural gas. The story of fossil fuels begins 300 to 400 million years ago -- long before dinosaurs roamed the Earth -- when much of the planet was covered in thickly vegetated swamps and prehistoric seas. Over the millennia, the decayed remains of dead plants and sea creatures piled up on seafloors and swamp beds.
Eventually, these ancient wetlands dried up and were covered with thick sedimentary layers of sand, soil and rocks. In some cases, new seas reappeared above them. The crushing downward pressure of all of these successive layers altered the chemical composition of the plant and animal remains, creating deep deposits of carbon-rich coal, oil and natural gas. When fossil fuels are burned through combustion, they release their carbon as heat (energy) and any impurities as emissions.
Fossil fuels are called nonrenewable energy sources, since it takes hundreds of millions of years for the Earth to produce new deposits of coal, oil and natural gas. According to the World Coal Institute, there is enough coal in the ground to last us 130 more years, while there are only enough oil and natural gas reserves to last another 42 and 60 years respectively. In contrast, biofuels are considered renewable energy sources since corn, soy and other biomass can be grown indefinitely.
In the United States, 93 percent of the energy we consume comes from fossil fuels. We burn them in the form of gasoline and diesel fuel for cars, home heating oil, natural gas for cooking and heat, and coal for electricity. Americans consume fossil fuels at a remarkable rate:
- 380 million gallons (1.4 billion liters) of gasoline every day
- 1.12 billion tons (1.06 trillion kilograms) of coal every year
- 19.4 million barrels of crude oil (refined to make gasoline, diesel fuel, jet fuel, propane and plastics) every day
Fossil fuels carry a range of health and environmental risks of fossil fuels, but we use them heavily because they are cheap and abundant. The U.S. is the world’s largest producer of coal, with mines in 26 of the 50 states. That’s why over half the electricity in America is produced at coal-burning power plants. Oil is another relatively cheap and plentiful commodity. If we wanted to replace the current nonrenewable gasoline supply with a renewable biofuel like ethanol, American farmers would have to set aside 675 million acres, or 71 percent of the country’s total cropland, to grow corn exclusively for fuel.