Although commonly associated with petroleum deposits it also occurs separately in sand, sandstone, limestone, and shale deposits. Some geologists theorize that natural gas is a byproduct of decaying vegetable matter in underground strata, while others think it may be primordial gases that rise up from the mantle. Because of its flammability and high calorific value, natural gas is used extensively as an illuminant and a fuel.
Natural gas was known to the ancients but was considered by them to be a supernatural phenomenon because, noticed only when ignited, it appeared as a mysterious fire bursting from the ground. One of the earliest attempts to harness it for economic use occurred in the early 19th cent. in Fredonia, N.Y. Toward the latter part of the 19th cent., large industrial cities began to make use of natural gas, and extensive pipeline systems have been constructed to transport gas. Since the late 20th cent., improvements in hydraulic fracturing, or
fracking —in which pressurized fluids are injected into a well to induce rock fractures that allow the release of natural gas—and its use in combination with horizontal drilling has permitted natural gas to extracted from previously untappable deposits of shale.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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