The Pasteur point is a level of oxygen (about 0.3% by volume which is less than 1% of Present Atmospheric Level or PAL) above which facultative aerobic microorganisms and

facultative anaerobes A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

adapt from

fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...

aerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

. It is also used to mark the level of oxygen in the early atmosphere of the Earth that is believed to have led to major evolutionary changes. It is named after

Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...

, the French microbiologist who studied anaerobic microbial fermentation, and is related to the Pasteur effect. It was once supposed that about 400 million years ago, in the

Cambrian period The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

, the level of oxygen in the atmosphere rose from 0.1 to 1 percent of present atmospheric level. Supposedly, this led to many organisms adapting from fermentation to respiration, leading to organisms evolving

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

and what is termed the

Cambrian explosion The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil record. ...

of species. It has also been suggested that this increased oxygen level reduced the influence of

ultraviolet radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

.Berkner, L. V. & Marshall, L. C. (1965). Oxygen and evolution. New Scientist, 28, 415-9. It is now well documented that oxygen level reached at least 10% of the present value 2.4 billion years ago (for details see

Great Oxygenation Event The Great Oxidation Event (GOE), also called the Great Oxygenation Event, the Oxygen Catastrophe, the Oxygen Revolution, the Oxygen Crisis, or the Oxygen Holocaust, was a time interval during the Paleoproterozoic era when the Earth's atmospher ...

References

Cambrian events Evolution of the biosphere Oxygen {{biochemistry-stub

See also

References