Our main sources for energy are largely dependent upon fossil fuels. They are used to heat and/or cool homes, produce electricity, and provide fuel for transportation. Fossil fuels are hydrocarbons that have been formed from the organic remains of prehistoric plants and animals. The three types of fossil fuels are coal, oil, and natural gas.
Coal is a solid fossil fuel that forms when heat and pressure change a plant material. This process usually takes millions of years to form in sedimentary rocks. Coal is mostly carbon with small amounts of sulfur and mercury. The formation of coal goes through four stages: peat, lignite, bituminous coal, and anthracite. Anthracite is the most desirable because it produces the most heat with the least amount of smoke compared to the other types of coal. Anthracite has the greatest amount of carbon content and the lowest sulfur content. Bituminous is the most commonly used type of coal for electric power in the United States. Coal is extracted from underground mines which is detrimental to the environment and is very dangerous for the miners. Burning coal pollutes the air with sulfur oxide, which in turn causes sulfuric acid to eventually fall to the ground in the form of acid precipitation. Coal produced about 42% of the electricity in the U.S. in 2011. The burning of coal supplies the energy to operate steam turbines that produce electricity. Coal is the world’s most abundant fossil fuel; but it is not as versatile as oil and natural gas.
Oil is a highly viscous liquid that can be used for heating, gasoline, and asphalt.
There are three geological processes that ultimately led to the existence of oil. Organic materials were buried by sediments faster than they were able to decay. Sea floors containing these sediments were subjected to the right amount of pressure and heat to turn the organic material into oil. Over time, oil collected in porous limestone or sandstone was capped off by shale or silt which kept it from escaping. Oil can be used to make a variety of products such as gasoline, kerosene, jet fuel, and plastics. When oil is burned, CO2 is released into the atmosphere which contributes to global warming.
Natural gas is often found above crude oil reservoirs and is composed primarily of methane. It is a gaseous fossil fuel. Although natural gas is a valuable energy resource, it is often wasted when it is burned off as a by-product of oil drilling. Natural gas is a versatile fossil fuel which could be used in fuel powered vehicles in place of gasoline with some engine modifications. When burned, natural gas produces less CO2 per unit of energy than either oil or coal. Since natural gas is still relatively abundant it is likely that the use of natural gas will increase.