Oxygen was discovered about 1772 by a Swedish chemist, Carl .... oxygen atmospher

Occurrence, properties, and uses The proportion of oxygen by volume in the atmosphere is 21 percent, by weight in seawater 89 percent, and in the Earth's crust 46.6 percent. (Certain recent figures suggest an even higher percentage of oxygen in seawater and in the Earth's crust.) During respiration, animals and some bacteria take oxygen from the atmosphere and return to it carbon dioxide, whereas by photosynthesis, green plants assimilate carbon dioxide in the presence of sunlight and evolve free oxygen. Gaseous oxygen on Earth and in the lower atmosphere consists almost entirely of molecules of two atoms, O . Commercial oxygen or oxygen-enriched air has replaced ordinary air in steelmaking and other metallurgical processes and in the chemical industry for the manufacture of such oxidation-controlled chemicals as acetylene, ethylene oxide, and methanol. Medical applications of oxygen include use in oxygen tents, inhalators, and pediatric incubators. oxygen atmospher