On September 26, four men and four women emerged from a glass-enclosed world in the Arizona desert for the first time in two years. It's no surprise that they took big gulps of Earth's air; the air inside their dome, called Biosphere 2, had lost quite a bit of life-giving oxygen.
Having enough oxygen for the Biospherians to breathe was a concern from the start. Biosphere 2 was supposed to be a self-sustaining world-within-a-world, a potential model for a colony in space (see SW ...