As of 2010, fossil fuels supplied 85 percent of the energy needs of the United States, according to the U.S. Department of Energy, (DOE). Fossil fuels come from deposits of dead plants and animals beneath the surface of the earth. These deposits were transformed into oil, natural gas and coal over millions of years by the tremendous weight and pressure of subsequent layers of rock and other materials piled on top of them.
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Oil or Petroleum
Petroleum, or oil, has been used by human societies worldwide for more than 5,000 years, according to the California Energy Commission (CEC). Ancient Egyptians used oil as medicine; Native Americans used it to waterproof their canoes. Before the middle of the 19th century, the source for most oil was liquefied coal or oil skimmed from lake surfaces.
Since 1859, when Edwin Drake constructed the first oil well in Titusville, Pennsylvania, underground and underwater reserves have been the main source of crude oil. Until 1970, the United States produced enough crude oil to meet all its energy needs, according to the "Journal of Energy Security." Since then, it has needed to import oil. Most of this country's imported oil comes from the Middle East, although Canada is the single largest provider, according to the CEC and the U.S. Energy Information Administration (EIA).
Natural gas is largely made up of a substance called methane, a compound of hydrogen and carbon. Natural gas is lighter than air, the CEC notes, and is colorless and odorles — the "rotten egg" odor from natural gas in your home comes from an additive that makes it easier to detect leaks. Natural gas is pumped to the Earth's surface and transmitted through pipelines to storage facilities, and ultimately to businesses and homes.
As of 2007, 80 percent of all the natural gas produced in the U.S. came from five states: Louisiana, New Mexico, Oklahoma, Texas and Wyoming, according to the Natural Gas website. The Alaska Natural Gas Pipeline project, which has gained preliminary approval from the state of Alaska, would stretch across Alaska from reserves located near Prudhoe Bay, according to the project website. Once completed in 2020, the pipeline would have one of two alternative destinations — a linkup with a pipeline system located in Alberta, Canada, which would proceed into the continental United States, or a shorter route ending in Valdez, Alaska.
Coal is a hard, black substance made of five elements: carbon, hydrogen, oxygen, nitrogen and sulfur, according to the CEC. There are three types of coal: anthracite, bituminous and lignite. Anthracite coal has the highest carbon content, and is the hardest . Bituminous has less, lignite the least. Peat is a substance that eventually becomes coal; it is also found in many areas and used for fuel. The United States has approximately 28 percent of all the world's coal reserves, according to the EIA.
Coal is mined from shafts dug deep into the earth, or by strip mines on the surface, the CEC reports. So-called "mountaintop removal" mining is a controversial practice that involves clear-cutting forests located in the mining area, then exposing the coal, according to the U.S. Environmental Protection Agency (EPA).
The Clean Coal Power Initiative provides incentives for producers to reduce sulfur, nitrogen and mercury emissions from power plants, according to the DOE. Other projects are devoted to developing more efficient methods of converting coal to electricity or other forms of energy. An additional $800 million in stimulus funding from the American Recovery and Reinvestment Act of 2009 was devoted to developing a means for beneficial reuse of carbon dioxide and carbon sequestration, or storage underground.