I used to have a biosphere and loved it. It survived a couple of years despite a very slow leak and more than once being stuck in a box for months after a move. As well as being pretty, they’re a neat little image of the world. The video above introduces the concept of building your own biosphere in a Kilner jar. The secret ingredient is pond scum.
This page has more biosphere information, including a series of experiments to see what works best.
Technorati tag: EcoHouse