In September 1991, eight people walked through an airlock in the Arizona desert and sealed themselves inside a glass building for two years. Biosphere 2 was meant to show that a working world could be built by hand. Earth was Biosphere 1. Inside were a rainforest, an ocean, a savanna, a mangrove marsh, a desert and a farm, arranged so that the plants would take up the carbon dioxide the people breathed out and give back the oxygen and food...