Oxygen

:This article is about the chemical element oxygen. For other usage, see Oxygen (disambiguation).

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:Newspapers sometimes say "oxygen cylinders" as an inaccurate reference to scuba gear.

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Oxygen is a chemical element in the periodic table. It has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe, usually bound with other elements. Unbound oxygen (usually called molecular oxygen, O2) appeared on Earth first as a product of the metabolic action of early anaerobes (archaea and bacteria). The atmospheric abundance of free oxygen in later geological epochs and up to the present has been largely driven by photosynthetic organisms, roughly three quarters by phytoplankton and algae in the oceans and one quarter from terrestrial plants.

Related Topics:
Chemical element - Periodic table - Atomic number - Earth - Universe - Metabolic - Anaerobe - Archaea - Bacteria - Photosynthetic - Phytoplankton - Algae - Plant

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