'Biospherian' Linda Leigh seen conducting a plant survey in the desert biome of the Biosphere 2 project. Biosphere 2 is a privately-funded experiment, designed to investigate the way in which humans interact with a small self-sufficient ecosystem, and to look at possibilities for future planetary colonisation. The $150 million Biosphere covers 3.1 acres near Tucson, Arizona, and was to be totally self-contained. The eight occupants shared their sealed-off world with 3,800 species of plant and animal life. After a two-year isolation, the project allegedly had problems with oxygen levels and food supply, and was criticised over its scientific validity.