Natural gas is a highly combustible odorless and colorless hydrocarbon gas largely composed of methane. It is produced in pressurized deposits located deep in the Earth's crust, commonly located just above oil deposits. The gas is created in roughly the same manner as oil, by geologic processes that act upon organic matter over millions of years. High combustibility coupled with low emissions makes it a highly valued resource. More economical than electricity, natural gas is primarily used for heating homes, cooking and running appliances such as water heaters and clothes dryers.
Early civilizations had an interesting relationship with natural gas. As it seeped from deep within the earth, occurrences such as lightening strikes occasionally ignited it. To ancient peoples, fire issuing from between rocks or from shallow marshlands with no visible combustible source took on divine or supernatural significance. One famous example is the legend of the "eternal flame" of Mount Parnassus, discovered by a Greek goat herder some 3,000 years ago. The temple of the Oracle of Delphi was purportedly erected around the fire, and the priestess issued prophecies inspired by the miraculous flames.
By 500 B.C., the Chinese found a way to put this gas to good use by creating rudimentary pipelines with bamboo stalks. Pinpointing areas where it was escaping the earth, they channeled the gas to fuel fires beneath pots of boiling seawater in order to make distilled drinking water.
In 1785, the United Kingdom commercialized an alternative natural gas manufactured from coal. Production spread to the United States after the turn of the century, but coal-manufactured gas was less clean and less efficient. In 1821, William Hart of New York dug the first well looking for naturally occurring gas and the first American gas company soon followed. Robert Bunsen invented the Bunsen burner in 1885, and by 1938 natural gas was a regulated resource in the United States.
Aside from natural deposits, tiny microorganisms called methanogens produce natural gas by breaking down organic matter. Methanogens reside in the intestines of humans and many animals, including cattle, and can also be found near the surface of the Earth in anaerobic conditions. These microorganisms are responsible for landfill gas, more properly termed biogenic methane, as distinguished from thermogenic methane, or deposited gas. Though a great deal of natural gas escapes into the air from various biogenic sources, efforts are underway to develop technology that can harvest it from unconventional sources. This would compliment natural deposits, which by some estimates are quite extensive.
According to the Energy Information Administration's data as of 2006, Russia has about 27% of the world's total reserves for deposited natural gas — the most of any single country. The Middle Eastern countries collectively have about 40% of the world's total reserves, with Iran having the greatest portion (about 14%). Africa and Asia each have around 8% with Asia having just a bit more than Africa. Central and South America together have about a 4% share — about the same as the United States.