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While there are many abiotic sources and sinks for O 2, the presence of the profuse concentration of free oxygen in modern Earth's atmosphere and ocean is attributed to O 2 production from the biological process of oxygenic photosynthesis in conjunction with a biological sink known as the biological pump and a geologic process of carbon burial involving plate tectonics.
Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium. [68] About 0.9% of the Sun's mass is oxygen. [19] Oxygen constitutes 49.2% of the Earth's crust by mass [69] as part of oxide compounds such as silicon dioxide and is the most abundant element by mass in the Earth's crust.
Oxygen began building up in the prebiotic atmosphere at approximately 1.85 Ga during the Neoarchean-Paleoproterozoic boundary, a paleogeological event known as the Great Oxygenation Event (GOE). At current rates of primary production, today's concentration of oxygen could be produced by photosynthetic organisms in 2,000 years. [4]
Oxygenic photosynthesis is the main source of oxygen in the Earth's atmosphere, and its earliest appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria , became important during the Paleoproterozoic era around two billion years ago.
All sources include superoxide, singlet oxygen, and hydroxyl radical. Hydrogen peroxide is not nearly as reactive as these species, but is readily activated and is thus included. [ 3 ] Peroxynitrite and nitric oxide are reactive oxygen-containing species as well.
Natural oxygen is made of three stable isotopes, 16 O, 17 O, and 18 O, with 16 O being the most abundant (99.762% natural abundance). Depending on the terrestrial source, the standard atomic weight varies within the range of [15.999 03, 15.999 77] (the conventional value is 15.999). 16 O
That has left goods – including medical oxygen and tuberculosis and HIV drugs – stuck, at risk of damage, expiry or even theft, while patients and doctors are unable to access critical tools ...
The rate of change of oxygen can be calculated from the difference between global sources and sinks. [26] The oxygen sinks include reduced gases and minerals from volcanoes, metamorphism and weathering. [26] The GOE started after these oxygen-sink fluxes and reduced-gas fluxes were exceeded by the flux of O 2 associated with the burial of ...