Biosphere 1 is the Earth.
Biosphere 2 is a human made, enclosed ecosystem in Oracle, Arizona where four men and four women lived for two years, beginning in 1991.
After this original group, another crew came in for six months in 1994.
The $150 million structure was built to see how well a human made and maintained ecosystem would hold up, with the idea that such colonies could perhaps be set up in remote locations like Mars.
Today the structure is open to the public for tours.
A Biosphere 3 is in remote northern Siberia and is uninhabited, and there may be a Biosphere 4 under construction in Japan.