Fossil fuels, which include coal, oil and natural gas, were formed millions of years ago when prehistoric plants and animals died, and their decaying bodies, pressed under layers of rock and earth, became fossilized. Life as we know it would not be possible without fossil fuels. Not only are they burned to supply heat and energy to homes and industry, but by forming the fuel for power stations, they also supply most of the electricity we use. In addition, fossil fuels can be processed to produce many other useful materials, including plastics, dyes and bitumen.
Fossil fuels include coal, petroleum, natural gas, oil shales, bitumen’s, tar sands, and heavy oils. All contain carbon and were formed as a result of geologic processes acting on the remains of organic matter produced by photosynthesis, a process that began in the Archean Eon (4.0 billion to 2.5 billion years ago). Most carbonaceous material occurring before the Devonian Period (419.2 million to 358.9 million years ago) was derived from algae and bacteria, whereas most carbonaceous material occurring during and after that interval was derived from plants.
All fossil fuels can be burned in air or with oxygen derived from air to provide heat. This heat may be employed directly, as in the case of home furnaces, or used to produce steam to drive generators that can supply electricity. In still other cases—for example, gas turbines used in jet aircraft—the heat yielded by burning a fossil fuel serves to increase both the pressure and the temperature of the combustion products to furnish motive power.
Since the beginning of the Industrial Revolution in Great Britain in the second half of the 18th century, fossil fuels have been consumed at an ever-increasing rate. Today they supply more than 80 percent of all the energy consumed by the industrially developed countries of the world. Although new deposits continue to be discovered, the reserves of the principal fossil fuels remaining on Earth are limited. The amounts of fossil fuels that can be recovered economically are difficult to estimate, largely because of changing rates of consumption and future value as well as technological developments. Advances in technology—such as hydraulic fracturing (fracking), rotary drilling, and directional drilling—have made it possible to extract smaller and difficult-to-obtain deposits of fossil fuels at a reasonable cost, thereby increasing the amount of recoverable material. In addition, as recoverable supplies of conventional (light-to-medium) oil became depleted, some petroleum-producing companies shifted to extracting heavy oil, as well as liquid petroleum pulled from tar sands and oil shales.
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