Eight people walked into a huge glass-and-steel building in Oracle, Arizona, on September 26, 1991, and locked the door behind them. They were not coming out for the next two years.
The facility was a 3.14-acre (1.27-hectare) airtight structure built to be a self-contained world, with a rainforest, an ocean with a coral reef, mangrove wetlands, a savannah grassland, a fog desert, farmland, and human living quarters. It's the largest closed ecological system ever created. The eight-man crew was to live off the system's production, breathing its air, drinking its recycled water, and growing their own food: a test run, in effect, for long-term human life in space.
