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Oxygen cycle
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The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere (air), the biosphere (living things), and the lithosphere (Earth's crust). The main driving factor of the oxygen cycle is photosynthesis, which is responsible for themodern Earth's atmosphere and life.

[edit] Reservoirs and Fluxes
By far the largest reservoir of Earths oxygen is within the silicate and oxide minerals of the crust and mantle (99.5%). Only a small portion has been released as free oxygen to the biosphere (0.01%) and atmosphere (0.36%). The main source of atmospheric oxygen is photosynthesis, which produces sugars and oxygen from carbon dioxideand water: 6CO2 + 6H2O + energy → C6H12O6 + 6O2 Photosynthesizing organisms include the plant life of the land areas as well as the phytoplankton of the oceans. The tiny marine cyanobacterium Prochlorococcus was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean.[1] An additional source of atmospheric oxygen comes from photolysis, whereby high energyultraviolet radiation breaks down atmospheric water and nitrite into component atoms. The free H and N atoms escape into space leaving O2 in the atmosphere: 2H2O + energy → 4H + O2 2N2O + energy → 4N + O2 The main way oxygen is lost from the atmosphere is via respiration and decay, mechanisms in which animal life and bacteria consume oxygen and release carbon dioxide.

Because lithospheric mineralsare oxidised in oxygen, chemical weathering of exposed rocks also consumes oxygen. An example of surface weathering chemistry is formation of iron-oxides (rust): 4FeO + O2 → 2Fe2O3 Main article: Mineral redox buffer Oxygen is also cycled between the biosphere and lithosphere. Marine organisms in the biosphere create calcium carbonate shell material (CaCO3) that is rich in oxygen. When the organismdies its shell is deposited on the shallow sea floor and buried over time to create the limestone rock of the lithosphere. Weathering processes initiated by organisms can also free oxygen from the lithosphere. Plants and animals extract nutrient minerals from rocks and release oxygen in the process.

[edit] Ozone
The presence of atmospheric oxygen has led to the formation of ozone and the ozonelayer within the stratosphere. The ozone layer is extremely important to modern life as it absorbs harmful ultraviolet radiation: O2 + uv energy → 2O O + O2 → O3

[edit] References
1. ^ Steve Nadis, The Cells That Rule the Seas, Scientific American, Nov. 2003 [1]
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Cloud, P. and Gibor, A. 1970, The oxygen cycle, Scientific American, September, S. 110-123 Fasullo, J., SubstituteLectures for ATOC 3600: Principles of Climate, Lectures on the global oxygen cycle, http://paos.colorado.edu/~fasullo/pjw_class/oxygencycle.html Morris, R.M., OXYSPHERE - A Beginners' Guide to the Biogeochemical Cycling of Atmospheric Oxygen, http://seis.natsci.csulb.edu/rmorris/oxy/Oxy.htm
Biogeochemical cycles Carbon cycle - Hydrogen cycle - Nitrogen cycle Oxygen cycle - Phosphorus cycle - Sulfurcycle - Water cycle

Retrieved from "http://en.wikipedia.org/wiki/Oxygen_cycle" Categories: Ecology | Geochemistry | Chemical oceanography | Photosynthesis
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Oxygen Cycling
Oxygen (O) atoms cycle through biosphere the way other elements Earth has a fixed supply of the be found everywhere, including the rocks, and all living organisms. need to breathe oxygen, there is every organism. the...