What would happen if oxygen were not available?
All life except for anaerobic organisms would die out.
Aerobic respiration requires oxygen. In aerobic respiration, one molecule of glucose is broken down to produce 34 to 36 molecules of ATP, the energy currency of the cell. If there was no oxygen available, aerobic respiration would stop and organsims that rely on aerobic respiration would die.
Overall equation for aerobic respiration
Without aerobic respiration, the anaerobic process of glycolysis produces a net yieldof 2 ATP from one glucose molecule.