Robert J. Bradbury wrote:
> Alternatively, and this is perhaps more interesting, if stresses like
> these are what it takes to get complex life, then the fire & ice
> planets that have highly eliptical orbits, might evolve complex, and
> even intelligent life, much quicker than did the Earth. That would
> imply that the "Rare Earth" arguments are pretty irrelevant. (But
> since the authors aren't biologists they may not discuss it [I've
> only gotten through the first couple of chapters so far].)
>
> I would think the strategies of hibernation, low-temperature
> antifreeze proteins, etc. combined with DNA preservation strategies
> found in Deinococcus radiodurans would allow the evolution of species
> that can tolerate the highly eliptical orbits. So complex life
> might be quite abundant. Those that do get a leg up in such
> environments are going to be hyper-evolving species compared
> with the rather pokey rates found on Earth.
I don't doubt that complex organisms capable of surviving such environments
are possible, but I have some reservations about the idea that they could
evolve locally. Before you can have organisms with lots of elaborate
adaptations for surviving extreme environmental swings, you have to have
simple organisms that don't have such adaptations. You need an environment
in which life can arise, solve the basic survival problems like energy
production and reproduction, and reach a level of complexity that allows
complex adaptations to evolve. That implies that a world that has a stable
period followed by wild climate swings may support interesting life, but one
that has always had extreme shifts may not evolve life in the first place.
Which leads me to what I found interesting about this whole theory. IMO it
should be rather unusual (to put it mildly) for a planet to undergo the
kinds of shifts the authors are talking about without completely wiping out
all life. You need a combination of surface gravity, water abundance, solar
energy levels and geography that falls within very narrow limits to get the
kind of behavior they describe. Disturb any one parameter by very much and
you either can't get large climate shifts, can't recover from one, or don't
have any enclaves where complex life can survive from one warm era to the
next.
Which, of course, would have interesting implications for the expected
abundance of sentient life in the universe.
Billy Brown
bbrown@transcient.com
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