Methane
Methane (CH4), the simplest of all organic compounds, is produced when organic matter is digested by bacteria in the absence of air, creating natural gas. This gas contains from 50 percent to 90 percent methane. Most natural gas lies with coal and oil deposits buried deep beneath the earth and is a product of the decomposition of ancient swamps and bogs. Like coal and oil, it is especially useful as a fuel for cooking, heating, and even the operation of some motor vehicles. Many factory furnaces burn methane gas, and utilities use it to generate electricity. Methane is also a key raw material for making solvents and other organic chemicals. It was first synthesized from carbon and hydrogen in 1904 by a Russian-American chemist, Vladimir Ipatiev (1867-1952). The gas is colorless, odorless, and nontoxic; when mixed with oxygen, it burns readily with a pale, slightly luminous flame.
People have been aware of methane's existence for thousands of years. As early as 940 b.c., the Chinese piped the gas through hollow bamboo rods and burned it to evaporate seawater and produce salt. Though it was used as a lighting fuel as early as the second century a.d., until modern scientific methods were developed, methane was regarded mainly as a natural marvel rather than a useful fuel. Ancient people may have accidentally discovered methane seeping up from the ground when they noticed that breathing the gas made them light-headed and uncoordinated. Thinking they were in the presence of a supernatural power, they erected temples of worship near these sites.
By the late 1700s, scientists had begun to explore the nature of gases more systematically. The earliest gases to be identified were carbon dioxide, hydrogen, and oxygen, but scientists were aware that some sort of "flammable air" could be found near marshes, swamps, cesspools, and dung heaps, where organic matter was in the process of decay. In the 1770s, Alessandro Volta, an Italian physicist, read a paper by Benjamin Franklin describing a natural source of flammable air. Volta's friend and fellow scientist, P. Carlo Giuseppe Campi, had discovered such a source of gas in Italy, and Volta, fascinated, began combing the countryside for the signs of gas in Italian marshes. His testing of these marsh gases began when he found a source of gas at Lago Maggiore in November 1776. Volta was able to isolate methane from the gas in 1778, and his careful experimentation with the combustion of gases also led directly to Antoine-Laurent Lavoisier's discovery of the composition of water in 1783. Although Volta later became famous for his work on electricity, it was the discovery of methane that gave his scientific reputation its first big boost.
In certain proportions, mixtures of methane and air can explode when ignited. This happened frequently in coal mines in the 1800s, when methane gas seeping from coal seams was ignited by the candles and lamps that miners carried to light their way. In 1815, Humphry Davy, a British chemist, tested samples of this explosive coal-gas, called "firedamp." He confirmed that it was mainly methane and that it would ignite only at high temperatures. Thus was born the Davy lamp, in which the flame is surrounded by wire gauze to dissipate heat and prevent ignition of flammable gases. This invention was the first giant step forward in the safety of coal mining.
After Ipatiev synthesized methane in 1904, the "manufactured gas" was first used in American cities as fuel for gas lights in the 1800s and early 1900s. As simple techniques were developed for extracting methane from coal or oil, and as more pipelines were built to bring natural gas from drilling fields to the cities, the value of methane as a convenient fuel and as a building block for the organic chemicals industry began to rise steadily. Today scientists are using new sources, such as sewage and waste in landfills, to produce methane. Furthermore, researchers are finding new ways to use methane--as fuel for cars and other vehicles, for example.
However, methane has also been implicated as a major contributor to the greenhouse effect, meaning that it can accumulate in the atmosphere, trap the earth's heat, and cause global warming. In addition to seeping from swamps, bogs, and rice paddies or leaking from pipelines, methane is emitted in large quantities by cows, termites, and other animals that digest plants. Although the concentration of methane in the atmosphere has increased rapidly in the past few decades, the latest scientific data show that this increase has slowed down. Research is focusing on identifying the natural sources of atmospheric methane via chemical "fingerprints."
Scientists are also studying sea-floor deposits of methane hydrate—single molecules of natural gas trapped within the crystals formed by frozen water molecules. In 1995, a team of oceanographers conducted the most extensive study of methane hydrate ever done up until that point, by drilling into a large pocket off the southeastern coast of the United States. Given new estimates of the vast size of such reserves, researchers are now assessing whether they might be future energy sources. On the other hand, some scientists have also speculated that methane released by methane hydrate might have contributed to major climate shifts in the past.
Methane is not restricted to the planet earth. In the early 1900s, astronomers used spectroscopy to photograph light waves being emitted from Jupiter and Saturn, the two largest planets in our solar system. The spectra of the light indicated that the atmospheres of these planets contain methane. Since then, astronomers have determined that all of the gas giants--Jupiter, Saturn, Uranus and Neptune--have atmospheres containing significant amounts of methane.
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