8 people enter sealed biosphere in survival experiment

Biosphere 2 was a sealed 3.14-acre glass and steel enclosure in the Arizona desert, built to test a self-sustaining artificial ecosystem.

Four men and four women called biospherians sealed themselves inside on 26 September 1991 for a two-year mission.

Oxygen levels dropped from 21% to 14% within the first sixteen months, causing health problems for the crew.

Microbes in the rich soil consumed oxygen faster than expected, and the resulting carbon dioxide reacted with calcium hydroxide in concrete through carbonation, masking the oxygen loss.