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Why did officials inject oxygen into Biosphere 2 during the first mission?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Biosphere 2
Biosphere 2 Biosphere 2, located in Oracle, Arizona, U.S., shown in 2008. The facility was originally developed to study survivability and assess whether humans were capable of building and living in self-sustaining colonies in outer space. It was later used as a scientific research facility.

During the first mission of Biosphere 2, officials injected oxygen into the facility because the crew experienced a significant decline in atmospheric oxygen levels, which dropped from approximately 20.9 percent to 14.2 percent over 17 months.1

This depletion caused the "Biospherians" to suffer from marked lethargy and difficulty breathing, raising serious concerns regarding their health and their ability to complete the mission. While the exact cause was initially unknown, it was later attributed to soil microorganisms that consumed oxygen and released carbon dioxide, as well as reduced photosynthesis due to increased cloud cover. Although the decision to inject oxygen was criticized for compromising the goal of creating a truly self-sustaining environment, it was deemed necessary to ensure the immediate safety and well-being of the crew.1