In 1991, eight people sealed themselves inside a glass world in the Arizona desert for two years, and the experiment nearly unravelled when the oxygen began disappearing from the air they were breathi

Key Points:

• In 1991, eight people entered Biosphere 2, a sealed three-acre glass and steel enclosure in Arizona, aiming to live for two years in a self-sustaining miniature Earth ecosystem; however, oxygen levels inside fell steadily, requiring outside oxygen to be pumped in.
• The oxygen decline was not due to leakage but resulted from microbial respiration in the soil consuming oxygen and producing carbon dioxide, which was then absorbed by the curing concrete structure, locking carbon dioxide into the walls as calcium carbonate.
• Although Biosphere 2 failed to maintain a breathable atmosphere without intervention, the experiment provided valuable insights into the complex interactions within closed ecological systems, highlighting the unexpected role of materials like concrete in atmospheric chemistry.
• The project faced criticism for its scientific rigor and was overshadowed by crew conflicts, leading to a second mission that ended prematurely; today, Biosphere 2 is operated by the University of Arizona for environmental research rather than sealed human habitation.
• The key lesson from Biosphere 2 remains the difficulty in accurately predicting the behavior of closed life-support systems before sealing, as demonstrated by the unanticipated oxygen decline and carbon dioxide absorption dynamics.