Oxygen Cycle

THE OXYGEN CYCLE allows for the regeneration of freely available diatomic oxygen (O2) in the atmosphere. Oxygen accounts by volume for approximately 21 percent of the atmosphere, is reactive with myriad inorganic and organic substances, and is vital to living organisms for aerobic respiration and energy production. The cycle involves any source of oxygen within the world, and is not limited to the oxygen animals must breathe to sustain life; any compound containing an atom of oxygen is considered part of the oxygen cycle. Furthermore, the cycle is composed of many distinct biological and geological chemical reactions that together allow oxygen initially consumed and lost from the atmosphere to be released back into the atmosphere.

These reactions take place among the three different primary reservoirs, or ...