Planes Earth has its own biosphere a biosphere is defined as being the atmosphere in which living organisms exist or that is capable of supporting life. Biosphere 2 is a completely separate and contained biosphere with no interaction with its parent biosphere of the Earth once it is sealed.
Biosphere 2 covers just over 1.3 hectares in Arizona construction finished 1991.Biosphere 2 aim was to allow the study and manipulation of a biosphere without damaging that of the earth’s as well as to learn more about the possibility of a manmade biosphere someday being built on say Mars.
The first fully sealed mission involved eight people sealing themselves into Biosphere 2 for a period of 2 years starting in 1991. The experiment was not altogether successful but provided several insights on how hard it is to manage a biosphere. CO2 levels fluctuated wildly and many of the animals, insects and birds sealed in with them died some that survived came to dominate and became pests.
A second mission started in 1994 failed due to outside forces.
I have attached a TED video of Jane Poynter on her experiences in Biosphere 2 it is well worth a watch
For further information on the project and the missions you can click here