What is the lowest percentage of atmospheric oxygen that any organism can survive in using aerobic respiration?
It has more to do with the partial pressure of Oxygen rather than percentage. At 15,000 feet altitude there is still 21% Oxygen, but you will only be getting half the Oxygen compared to sea level. People can go down to 10% Oxygen at sea level before you get impairment, below 5% you will die. I have personally breathed an atmosphere 10% Oxygen, 5% CO2 and Argon. There are microbes which can survive a Martian atmosphere.
