If you can cough up the millions, you can buy Biosphere 2, a giant terrarium built in the Arizona desert that houses a sampling of the earth’s ecological systems. The steel-framed glass structure, built in 1991 by a Texas oil billionaire, was used by Columbia University as a research center from 1996 to 2003, after completion of the original Biosphere project, in which eight people were to live in the dome for two years without any contact with the world outside the building. The experiment was discredited when it was discovered that oxygen was being supplied from an outside source.