Just to give some scale here: A human uses about 0.84 kilograms O2 per day. There is about 5e18 kg O2 in the atmosphere. Excluding all other sources of O2 con

Just to give some scale here: A human uses about 0.84 kilograms O2 per day. There is about 5e18 kg O2 in the atmosphere. Excluding all other sources of O2 consumption and replenishment, it would take about 500000 years for the current population of humans to "use up" all the current O2.