Biosphere 2 is an artificial biosphere in Oracle, Arizona built by Edward P. Bass, Space Biosphere Ventures and others. It was used to test if and how people could live and study in a closed biosphere, while carrying out scientific experiments. It explored the possible use of closed biospheres in space colonization, and also allowed the study and manipulation of a biosphere without harming Earth's. The name comes from the idea that it is modelled on "Biosphere 1" - Earth.
Some economists have used the price of the Biosphere 2 project as an input to value of life calculations, and attempts to calculate the total value of all natural capital on Earth. According to them: given that it does at least as good a job at sustaining humans as Biosphere 2, it should be worth at least as much per resident. This leads to a rather large, but finite, price of Earth itself.
New Scientist: The Last Word: Biosphere "Hypothetically (because otherwise my mum would get mad), if I were to put my brother in a perfectly sealed room, how much plant life would I need in that room in order to maintain a balance of oxygen and carbon dioxide such that both my brother and my beloved plants continue to live?"