Image obtained from http://www.accessexcellence.com/AB/GG/photo_Resp.html
Sources of Oxygen:
1) photodisassociation of H2O vapor
Since oxygen is so reactive its cycling is complex:
1) As a constituent of CO2 it circulates freely
throughout the biosphere.
2) Some CO2 combines with Ca to form carbonates.
3) O2 combines with nitrogen compounds to form
4) O2 combines with iron compounds to form ferric
5) Photosynthesis and respiration
6) O2 in the troposphere is reduced to O3 (ozone).
Ground level O3 is a pollutant which damages lungs.
[Phosphorus Cycle; Sulfur Cycle; Nitrogen Cycle; Carbon Cycle]