Abiogenic petroleum origin

Although the existence of hydrocarbons on extraterrestrial bodies like Saturn's moon Titan indicates that hydrocarbons are sometimes naturally produced by inorganic means, abiogenic petroleum origin is a largely discredited hypothesis which proposes that most of earth's petroleum and natural gas deposits were also formed inorganically. Mainstream theories about the formation of hydrocarbons on earth point to an origin from the decomposition of long-dead organisms. Theories explaining the origin of petroleum as abiotic are generally not well accepted by the scientific community, and are rejected by most researchers and scientific theories on the subject. (Terrestrial natural gas is composed primarily of methane). Some comets contain massive amounts of organic compounds, the equivalent of cubic kilometers of such mixed with other material; for instance, corresponding hydrocarbons were detected during a probe flyby through the tail of Comet Halley in 1986. Drill samples from the surface of Mars taken in 2015 by the Curiosity rover's Mars Science Laboratory have found organic molecules of benzene and propane in 3 billion year old rock samples in Gale Crater.
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