Abiogenic petroleum origin
Abiogenic petroleum origin is a term used to describe a number of different theories which propose that petroleum and natural gas are formed by inorganic means rather than by the decomposition of organisms. The two principal abiogenic petroleum theories, the deep gas theory of Thomas Gold and the deep abiotic petroleum theory, have been scientifically discredited and are obsolete. Scientific opinion on the origin of oil and gas is that all natural oil and gas deposits on Earth are fossil fuels, and are therefore not abiogenic in origin. There are a few abiogenic petroleum theories which are still subject to ongoing research and which typically seek to explain the existence of smaller quantities of oil and gas.Some abiogenic theories have proposed that oil and gas did not originate from fossil deposits, but have instead originated from deep carbon deposits, present since the formation of the Earth. Other hypotheses have suggested that hydrocarbons may have arrived on Earth from solid bodies such as comets and asteroids from the late formation of the Solar System, carrying hydrocarbons with them.Some abiogenic hypotheses gained limited popularity among geologists over the past several centuries. Scientists in the former Soviet Union widely held that significant petroleum deposits could be attributed to abiogenic origin, though this view fell out of favor toward the end of the 20th century because they did not make useful predictions for the discovery of oil deposits. It is generally accepted that abiogenic formation of petroleum has insufficient scientific support and that oil and gas fuels on Earth are formed almost exclusively from organic material.