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Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium.[67] About 0.9% of the Sun's mass is oxygen.[18] Oxygen constitutes 49.2% of the Earth's crustby mass[68]as part of oxide compounds such as silicon dioxideand is the most abundant element by mass in the Earth's crust.
Geological history of oxygen. O 2 build-up in the Earth's atmosphere. Red and green lines represent the range of the estimates while time is measured in billions of years ago (Ga). Stage 1 (3.85–2.45 Ga): Practically no O 2 in the atmosphere. Stage 2 (2.45–1.85 Ga): O 2 produced, but absorbed in oceans and seabed rock.
The Great Oxidation Event (GOE) or Great Oxygenation Event, also called the Oxygen Catastrophe, Oxygen Revolution, Oxygen Crisis or Oxygen Holocaust, [2] was a time interval during the Earth 's Paleoproterozoic era when the Earth's atmosphere and shallow seas first experienced a rise in the concentration of free oxygen. [3]
Oxygen saturation is the fraction of oxygen -saturated haemoglobin relative to total haemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial blood oxygen saturation levels in humans are 96–100 percent. [ 1 ]
Dark oxygen. Dark oxygen production refers to the generation of molecular oxygen (O 2) through processes that do not involve light-dependent oxygenic photosynthesis. The name therefore uses a different sense of 'dark' than that used in the phrase "biological dark matter" (for example) which indicates obscurity to scientific assessment rather ...
The oxygen cycle is the biogeochemical cycle of oxygen atoms between different oxidation states in ions, oxides, and molecules through redox reactions within and between the spheres/reservoirs of the planet Earth. [1] The word oxygen in the literature typically refers to the most common oxygen allotrope, elemental/diatomic oxygen (O 2), as it ...
Liquid oxygen has a clear cyan color and is strongly paramagnetic: it can be suspended between the poles of a powerful horseshoe magnet. [2] Liquid oxygen has a density of 1.141 kg/L (1.141 g/ml), slightly denser than liquid water, and is cryogenic with a freezing point of 54.36 K (−218.79 °C; −361.82 °F) and a boiling point of 90.19 K (−182.96 °C; −297.33 °F) at 1 bar (15 psi).
There are three known stable isotopes of oxygen (8 O): 16O, 17O, and 18O. Radioactive isotopes ranging from 11O to 28O have also been characterized, all short-lived. The longest-lived radioisotope is 15O with a half-life of 122.266 (43) s, while the shortest-lived isotope is the unbound 11O with a half-life of 198 (12) yoctoseconds, though half ...