On 26 September 1993, the 8 men and women crew members of the Biosphere 2 experiment stepped back into Earth's atmosphere. For 2 years, they had lived inside the sealed ecosystem of Biosphere 2, a privately-funded, $150 million project near Tucson, Arizona. The huge and striking Biosphere 2 buildings cover 1.2 hectares and contain seven biomes (biological areas) - rainforests, savannah, marsh, ocean, desert, agriculture, human - and some 3800 plant and animal species. The 4 women and 4 men in the crew grew some 80 percent of their own food. The aim of Biosphere 2 is to investigate closed ecological system for scientific research, education, and as a step towards humans living on other planets, particularly Mars.