Most fossil fuels formed approximately 360 to 286 million years ago during the Carboniferous period of the Paleozoic Era. Tree- and plant-filled swamps covered the earth during this period.
Fossil fuels formed from the decomposing remains of organisms placed under immense pressure and heat for hundreds of millions of years. This long process resulted in energy-laden coal, natural gas and oil.
Fossil fuels are currently cheaper and more readily available for both commercial and residential uses.
Fossil fuels must be burned to release their stored energy. This combustion process also releases various particulates and emissions into the environment.
Fossil fuel emissions have been associated with the greenhouse effect, global warming, acid rain and human health issues, such as immune system changes and lung problems.
According to the U.S. Department of Energy, as of 2009, fossil fuels provided over 85 percent of the energy used in the United States. SolcomHouse.com reports that while the United States contains only about 4 percent of the global population, it uses over 25 percent of the world's fossil fuel resources.