Well, the question there is where does the Earth's O2 supply come from. The answer is what we should set up on the moon, a viable ecosystem. This means things

Well, the question there is where does the Earth's O2 supply come from. The answer is what we should set up on the moon, a viable ecosystem. This means things like hydroponics, probably at least some algae based systems, that kind of thing. That way we can regenerate the CO2 back into O2, and get some food production along the way!