Abiogenic petroleum origin is a body of hypotheses which propose that petroleum and natural gas deposits are mostly formed by inorganic means, rather than by the decomposition of organisms. Thomas Gold's deep gas hypothesis states that the origin of some natural gas deposits were formed out of hydrocarbons deep in the earth's mantle. Theories explaining the origin of petroleum as abiotic, however, are generally not well accepted by the scientific community. Abiogenic petroleum origin is a body of hypotheses which propose that petroleum and natural gas deposits are mostly formed by inorganic means, rather than by the decomposition of organisms. Thomas Gold's deep gas hypothesis states that the origin of some natural gas deposits were formed out of hydrocarbons deep in the earth's mantle. Theories explaining the origin of petroleum as abiotic, however, are generally not well accepted by the scientific community. Earlier studies of mantle-derived rocks from many places have shown that hydrocarbons from the mantle region can be found widely around the globe. However, the content of such hydrocarbons is in low concentration. While there may be large deposits of abiotic hydrocarbons, globally significant amounts of abiotic hydrocarbons are deemed unlikely. Some abiogenic hypotheses 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. Additionally, it has been 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. The abiogenic hypothesis regained some support in 2009 when researchers at the Royal Institute of Technology (KTH) in Stockholm reported they believed they had proven that fossils from animals and plants are not necessary for crude oil and natural gas to be generated. In his 2014 publication Chemistry of the Climate System, German chemist Detlev Moller documents sufficient reliable evidence to show that both processes can be shown to co-exist, that they're not mutually exclusive. An abiogenic hypothesis was first proposed by Georgius Agricola in the 16th century and various additional abiogenic hypotheses were proposed in the 19th century, most notably by Prussian geographer Alexander von Humboldt, the Russian chemist Dmitri Mendeleev (1877) and the French chemist Marcellin Berthelot. Abiogenic hypotheses were revived in the last half of the 20th century by Soviet scientists who had little influence outside the Soviet Union because most of their research was published in Russian. The hypothesis was re-defined and made popular in the West by Thomas Gold who developed his theories from 1979 to 1998, and published his research in English. Abraham Gottlob Werner and the proponents of neptunism in the 18th century regarded basaltic sills as solidified oils or bitumen. While these notions proved unfounded, the basic idea of an association between petroleum and magmatism persisted. Alexander von Humboldt proposed an inorganic abiogenic hypothesis for petroleum formation after he observed petroleum springs in the Bay of Cumaux (Cumaná) on the northeast coast of Venezuela.He is quoted as saying in 1804, 'the petroleum is the product of a distillation from great depth and issues from the primitive rocks beneath which the forces of all volcanic action lie'. Other early prominent proponents of what would become the generalized abiogenic hypothesis included Dmitri Mendeleev and Berthelot. In 1951, the Soviet geologist Nikolai Alexandrovitch Kudryavtsev proposed the modern abiotic hypothesis of petroleum. On the basis of his analysis of the Athabasca Oil Sands in Alberta, Canada, he concluded that no 'source rocks' could form the enormous volume of hydrocarbons, and therefore offered abiotic deep petroleum as the most plausible explanation. (Humic coals have since been proposed for the source rocks.) Others who continued Kudryavtsev's work included Petr N. Kropotkin, Vladimir B. Porfir'ev, Emmanuil B. Chekaliuk, Vladilen A. Krayushkin, Georgi E. Boyko, Georgi I. Voitov, Grygori N. Dolenko, Iona V. Greenberg, Nikolai S. Beskrovny, and Victor F. Linetsky. Astronomer Thomas Gold was a prominent proponent of the abiogenic hypothesis in the West until his death in 2004. More recently, Jack Kenney of Gas Resources Corporation has come to prominence, supported by studies by researchers at the Royal Institute of Technology in Stockholm. Within the mantle, carbon may exist as hydrocarbons—chiefly methane—and as elemental carbon, carbon dioxide, and carbonates. The abiotic hypothesis is that the full suite of hydrocarbons found in petroleum can either be generated in the mantle by abiogenic processes, or by biological processing of those abiogenic hydrocarbons, and that the source-hydrocarbons of abiogenic origin can migrate out of the mantle into the crust until they escape to the surface or are trapped by impermeable strata, forming petroleum reservoirs.