Organic origin theory
Among the many evidences supporting the origin of hydrocarbons from a fundamental organic component, three constitute the main assumption:
- hydrocarbons are found in sedimentary rocks that contain substantial amounts of organic matter;
- the presence of nitrogen and porphyrin pigments found in hydrocarbons is typical of plant and animal matter, lacking in inorganic matter;
- optical activity, recorded in the components of petroleum, is characteristic of biological synthesis, not having been found in hydrocarbons derived from inorganic matter.
Regarding the starting material from which hydrocarbons originate (animal or plant origin), a mixed origin has been found in most cases. However, among all the organisms that may contribute to the process of naphthogenesis, marine ones play a fundamental role, even if they must be associated, subordinately, with those of continental origin. In particular, an important place is given to plankton, both animal and vegetable, followed by algae and animal organisms (fossil and microfossil) among which a rather important role is played by corals, which, as building organisms, constitute very porous rocky masses, often impregnated with hydrocarbons.
Among the continental organisms, the most important role is that of plants, in the form of both humic and woody substances. The transformations of these substances occur through a source of energy that originates from several factors: pressure and temperature, radioactivity, catalytic action of some metals (nickel, vanadium, molybdenum) and the presence of bacteria that act as triggers for chemical reactions.
To all this must be added the environmental conditions in which the process of naphthogenesis occurs. In this sense, particular importance is linked to the agents of decomposition, from which the organic matter must be removed before it is completely destroyed.
The best preservation conditions are represented, therefore, by those sea basins where organic matter accumulates and is preserved because of either the depth or the poor circulation of the waters which, not being oxygenated, determine anaerobic and reducing conditions. The persistence of these conditions must also be coupled with a continuous and regular subsidence of the bottom, so as to compensate for the contribution of sediment and not cause drastic changes to the environment.