Built in the late 1980s with $150 million in funding from Texas oil magnate Edward Bass, Biosphere 2 was designed as an airtight replica of Earth's environment (Biosphere 1). This 7,200,000-cubic-foot sealed glass and space-frame structure contains 5 biomes, including a 900,000-gallon ocean, a rain forest, a desert, agricultural areas and a human habitat.

By building Biosphere 2 and sealing people inside, they hoped to learn what problems would arise from living in a closed system. So it was that in 1991, a colony of 8 people set about to live inside Biosphere 2 for two years. However, over the two years, oxygen levels in Biosphere 2 dipped as dangerous levels of nitrous oxide rose. It became tough going for the live-in guests. Their personalities changed becoming hostile; they had trouble sleeping and they lost weight without protein in their diets. These experiments were suspended in 1994 and no future human habitation is planned.

Biosphere 2 is located on Arizona Route 77 north of Oro Valley.