That's true, but I'd say that the majority of real threats to civilization
in future will be human-made, not natural (with the possible exception of
nearby supernovas, etc, for which we can do little until we can dismantle
stars). Assuming we get past the year-2000 bug, anyway.
>If you hit an O'Neill cylinder with a rock, it dies. If you hit the
>Earth with a rock -- anything much smaller than Phobos -- well, a few
>species may go extinct, but the whole system will pick itself up and
>carry on as before.
Hit the Earth with a lump of rock fired from a mass-driver at Alpha
Centauri at 99% of the speed of light, and it dies. Earth wouldn't
be an easy target to hit that way, but a habitat would be almost
impossible.
>Of course, why the hell are we talking about habitats to support an
>agriculture-based society when there's the open question of what kind
>of habitat is appropriate to an uploaded mind to discuss?)
The same energy and resource problems still apply; there's still
little point in colonising Mars rather than turning it into habitats.
Mark