Pictures of the construction and setup of Biosphere 2, a compound intended to function as a self-sustaining ark for human life.This privately funded scale model of planet earth (Biosphere 1) was an ecological experiment, but it also explored the possibility of human colonies in outer space.The pictures were taken before the first closed mission began in 1991, when 4 women and 4 men walked through the airlocks and sealed themselves off for two years.The inhabitants were soon plagued by food shortages and dangerously low oxygen levels. Project supervisors resorted to pumping supplementary oxygen into the sealed space. If anything, the experiment has shown the difficulty of creating a self- sustaining environment. Project:Biosphere 2,by Space BiosphereVentures;Oracle,AZ,USA,1991. Photos: Kevin Kelly