In September 1991, eight people moved into Biosphere 2, a nearly airtight glass and steel complex in the Arizona desert. The half-acre farm at its centre would supply all their food. Plants, algae and photosynthesizing microorganisms would supply all their oxygen. If things went according to plan, they would have everything they needed to survive inside for two years – but a lot of people were betting against them.

Mark Nelson wrote a book about his time in Biosphere 2 called Pushing Our Limits. Archival footage in this episode was provide by the Institute of Ecotechnics.