> That wouldn't prevent one off extinction type events like asteroids. We can improve our understanding of ecology by trying to design such systems for lunar colony artificial biospheres.
To be kind of blunt, even an extinction-level asteroid hit with near-total biosphere destruction is probably still more conducive to human life than any other planet or satellite in the solar system, as evidenced by the continued existence of at least a few forms of life past the extinction event. And many of the events people worry about are far less destructive than even that (nuclear winter, for example, would probably roll Earth's climate back to pre-industrial temperatures, maybe as far as Little Ice Age, which is, uh, nowhere near extinction-level threat to humanity).
It's also worth pointing out that it's possible to do closed ecological studies without the expense of running it in space (e.g., Biosphere 2). The only thing you need space for studying in that regard is "what is the effect of non-1g environments on biological forms?" (to which existing studies suggest the answer is somewhere between "bad" and "horrible").
To be kind of blunt, even an extinction-level asteroid hit with near-total biosphere destruction is probably still more conducive to human life than any other planet or satellite in the solar system, as evidenced by the continued existence of at least a few forms of life past the extinction event. And many of the events people worry about are far less destructive than even that (nuclear winter, for example, would probably roll Earth's climate back to pre-industrial temperatures, maybe as far as Little Ice Age, which is, uh, nowhere near extinction-level threat to humanity).
It's also worth pointing out that it's possible to do closed ecological studies without the expense of running it in space (e.g., Biosphere 2). The only thing you need space for studying in that regard is "what is the effect of non-1g environments on biological forms?" (to which existing studies suggest the answer is somewhere between "bad" and "horrible").