Since the early 1920s, most petroleum geologists have favored a biogenic theory for the formation of oil. According to this theory, organic matter became buried in sediments, and subsequent over time transformed it into oil.
Since 1979 an opposing abiogenic theory about the origin of oil has been promulgated. According to this theory, what is now oil began as hydrocarbon compounds within the earth’s mantle (the region between the core and the crust) during the formation of the earth. Oil was created when gases rich in methane, crustal plates provided the conduits and fractures necessary for the gases to rise through the crust.
Opponents of the abiogenic theory charge that hydrocarbons could not exist in the mantle, because high temperatures would destroy or break them down. Advocates of the theory, however, point out that other types of carbon exist in the mantle: unoxidized carbon must exist there, because diamonds are formed within the mantle before the higher temperatures, allowing hydrocarbons, like unoxidized carbon, to continue to exist in the mantle.
If the abiogenic theory is correct, vast undiscovered reservoirs of oil and gas—undiscovered because the biogenic model precludes their existence—may in actuality exist. One company owned by the Swedish government has found the abiogenic theory so persuasive that it has started exploratory drilling for gas or oil in a granite formation call that prior to the start of drilling, methane gas had been detected rising through the granite.
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