How often does oxygen cycle through the atmosphere?
Volcanic and organic reactions.
Volcanos release huge volumes of water. The water undergoes disassociation due to cosmic radiation breaking into Oxygen and Hydrogen. The Oxygen then becomes part of the atmosphere.
Plants in the process of photosynthesis release Oxygen into the atmosphere. Plants, and animals in the process of cellular respiration burn Oxygen taking Oxygen out of the atmosphere.
Cellular respiration produces Carbon Dioxide which is used in photosynthesis to produce Oxygen.
Photosynthesis and Cellular Respiration by living organisms create a circle or cycle for the Oxygen in the atmosphere. Water also is released into the atmosphere by volcanos creates Oxygen.