Fossil fuels are buried deposits of petroleum, coal, peat, natural gas, and other carbon-rich organic compounds derived from the dead bodies of plants and animals that lived many millions of years ago. Over long periods of time, pressure and heat generated by overlying sediments concentrate and modified these materials into valuable energy sources for human purposes. Fossil fuels currently provide about 90% of all commercial energy used in the world. They provide the power to move vehicles, heat living spaces, provide light, cook our food, transmit and process information, and carry out a wide variety of industrial processes. It is no exaggeration to say that modern industrial society is nearly completely dependent on (some would say addicted to) a continual supply of fossil fuels. How we will adapt as supplies become too limited, too remote, too expensive, or too environmentally destructive to continue to use is a paramount question for society.
The amount of fossil fuels deposited over history is astounding. Total coal reserves are estimated to be in the vicinity of ten trillion metric tons. If all this resource could be dug up, shipped to market, and burned in an economically and environmentally acceptable manner, it would fuel all our current commercial energy uses for several thousand years. Petroleum (oil) deposits are thought to have originally amounted to some four trillion barrels (600 billion metric tons), about half of which has already been extracted and used to fuel industrial society. At current rates of use the proven oil reserves will be used up in about 40 years. World natural gas supplies are thought to be at least 10 quadrillion cubic feet or about as much as energy as the original oil supply. At current rates of use, known gas reserves should last at least 60 years. If we substitute gas for oil or coal, as some planners advocate, supplies will be used up much faster than at current rates. Some unconventional hydrocarbon sources such as oil shales and tar sands might represent an energy supply equal to or even surpassing the coal deposits on which we now depend.
In the United States, oil currently supplies about 40% of all commercial energy use, while coal contributes about 22%, and natural gas provide about 24%. Oil and its conversion products, such as gasoline, kerosene, diesel fuel, and jet fuel are the primary fuel for internal combustion engines because of the ease with which they can be stored, transported, and burned. Coal is burned primarily in power plants and other large, stationary industrial boilers. Methane (natural gas) is used primarily for space heating, cooking, water heating, and industrial processes. It is cleaner burning than either oil or coal, but is difficult to store or to ship to places not served by gas pipelines.
The use of fossil fuels as our major energy source has many adverse environmental effects. Coal mining often leaves a devastated landscape of deep holes, decapitated mountain tops, toxic spoil piles, and rocky rubble. Acid drainage and toxic seepage from abandoned mines poisons thousands of miles of streams in the United States. Every year the 900 million tons of coal burned in the U.S. (mainly for electric power generation) releases 18 million tons of sulfur dioxide, five million tons of nitrogen oxides (the main components of acid rain), four million tons of carbon monoxide and unburned hydrocarbons, close to a trillion tons of carbon dioxide, and a substantial fraction of the toxic metals such as mercury, cadmium, thallium, and zinc into our air. Coal often contains uranium and thorium, and that most coal-fired power plants emit significant amounts of radioactivity—more, in fact, than a typical nuclear power plant under normal conditions. Oil wells generally are not as destructive as coal mines, but exploration, drilling, infrastructure construction, waste disposal, and transport of oil to markets can be very disruptive to wild landscapes and wildlife. Massive oil spills, such as the grounding of the Exxon Valdez on Prince William Sound, Alaska, in 1989, illustrate the risks of shipping large amounts of oil over great distances. Nitrogen oxides, unburned hydrocarbons, and other combustion byproducts produced by gasonine and diesel engines are the largest source of air pollution in many American cities.
One of the greatest concerns about our continued dependence on fossil fuels is the waste carbon dioxide produced by combustion. While carbon dioxide is a natural atmospheric component and is naturally absorbed and recycled by photosynthesis in green plants, we now burn so much coal, oil, and natural gas each year that the amount of carbon dioxide in the atmosphere is rapidly increasing. Because carbon dioxide is a greenhouse gas (it is transparent to visible light but absorbs long wavelength infrared radiation), it tends to trap heat in the lower atmosphere and increase average global temperatures. Climatic changes brought about by higher temperatures can result in heat waves, changes in rainfall patterns and growing seasons, rising ocean levels, and could increase the frequency and severity of storms. These potentially catastrophic effects of global climate change may limit our ability to continue to use fossil fuels as our major energy source. All of these considerations suggest that we urgently need to reduce our dependency on fossil fuels and turn to environmentally benign, renewable energy sources such as solar power, wind, biomass, and small-scale hydropower.
- Fossil and Fossilization - The Fossil Clock, From Biosphere To Lithosphere, From Field To Laboratory, Interpreting The Fossil Record
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