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| Occurrence and Production of Oxygen |
 Occurrence
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| In nature, free oxygen is produced by the light-driven splitting of water during oxygenic photosynthesis in cyanobacteria, green algae and plants. Algae produce about 73 to 87 percent of the net global production of oxygen, which makes it available to humans and other animals for respiration. Another major source of oxygen is trees. Trees can absorb carbon dioxide at the rate of 26 pounds per year - especially young trees that are still growing - while releasing oxygen into the air. |
| In the laboratory and industrially, oxygen can be produced through electrolysis of water into oxygen and hydrogen. A similar method is the electrocatalytic oxygen evolution from oxides and oxoacids. Chemical catalysts can be used as well, such as in chemical oxygen generators or oxygen candles that are used as part of the life support equipment on spacecraft and submarines. |