If there was one person left on earth, how long would it be until all the air ran out?

Question

Given that the person had an incredibly long life span, therefore the only way he/she died would be air on the Earth running out. Also given that there are no trees or oxygen producers. This idea just randomly came to me, thanks!

Answer 1

Odd question....

You would have to find out how much oxygen we consumed in each breath, find out how much oxygen there is in the atmosphere, and find out the lowest concentration of oxygen which will keep us alive.  I know we can't survive on a concentration much lower than it is presently in the atmosphere.

Of course, if there was no photosynthesis, your long-lived friend would have more immediate worries than the air running out.