On September 26, 1991, eight individuals entered Biosphere 2, a three-acre glass and steel dome near Oracle, Arizona. They committed to living there for two years, relying solely on what the biosphere could provide. However, as time went on, the oxygen inside the dome began to drop dangerously low, prompting the team to pump in external oxygen.
The intriguing part? The oxygen didn’t just disappear. Understanding where it went became a significant mystery of the mission.
Biosphere 2 aimed to mimic Earth’s biosphere, which they called Biosphere 1. Inside were five biomes: a rainforest, an ocean with a coral reef, a mangrove wetland, a savannah, and a desert, along with areas for agriculture and human habitation. The project mixed ecology with a forward-looking goal: to learn about life-support systems for future space habitats.
Though ambitious, the project faced many criticisms. It was often seen as more of a spectacle than a scientific endeavor. According to a 2025 NPR report, the focus shifted from science to the personal conflicts among the crew, overshadowing the original goals.
Inside the biosphere, oxygen started at a normal level of 21%. But soon, the levels began to fall dramatically, reaching about 14% by the time outside oxygen was added. This was equivalent to the oxygen level at around 4,000 meters above sea level. The crew, who worked physically demanding jobs, began to feel exhausted and breathless. The mystery deepened: the drop in oxygen couldn’t simply be explained by an increase in carbon dioxide.
Researchers discovered that the loss of oxygen stemmed from two main factors. First, the rich soil in the agricultural areas housed numerous microbes that consumed oxygen at a high rate. However, the second issue was unexpected: the concrete structure absorbed carbon dioxide. This was because the biosphere’s walls included uncured concrete, which naturally takes in carbon dioxide as it hardens. So, as microbes consumed oxygen, the resulting carbon dioxide was then drawn into the concrete. The oxygen hadn’t vanished; it had just moved to the walls.
Some argue that this episode signals the failure of Biosphere 2. True, it couldn’t maintain a breathable atmosphere without intervention. For a long-term habitat, that is a critical shortfall. Yet, as an experiment, it revealed important truths about closed systems. The interaction between soil, microbes, and concrete demonstrated something unexpected: every element within a closed habitat influences the environment, including those we might overlook.
After the first crew completed their mission in 1993, a second attempt began in 1994 but lasted only six months due to management issues. The facility changed hands several times and is now run by the University of Arizona as a research center for environmental studies.
The lasting question from Biosphere 2 isn’t merely whether humans can live in a sealed environment. It’s about how much we can predict the behavior of such systems before sealing them off. The oxygen dropout highlighted just how hard it can be to foresee the outcomes in a closed ecosystem.
Source link
