On Sat, 18 Mar 2000 hal@finney.org wrote:
> The big problem I always had with the Gaia idea is that organisms can
> control their internal environmens only because they have evolved this
> ability over many generations. Early organisms were probably bad at it,
> but those which were slightly better survived and reproduced, and over
> time the ability improved.
Well, it is pretty clear that it is valid to the degree that the
organisms convert the CO2 to O2 (because they want the carbon).
The C gets bound to Ca (because CaCO3 is a good shell (defense)
when you can't make SiC or diamond). The planet itself through
plate tectonics seems to be the fundamental recycler of the
C by converting it back into CO2 released by the volcanoes.
Of course as Rare Earth does discuss there are numerous
ways for this to get messed up. It would be interesting
to know how many living organisms, the average C atom has
been through at this point.
It turns out Rare Earth does have a chapter on Snowball Earth.
They also touch briefly on the possibility that "extinction"
events might be good for organisms if there are many species
in a phyla (high diversity) since if even a few species can
survive the event, they can rapidly repopulate the empty
environmental niches. One thing that seems clear is that
that evolution starts slow and seems to speed up over time.
For example, bacterial "sex" seems to be much less effective
than higher order sex, because less genetic material is shuffled.
An interesting idea is that retroviruses and gene shuffling
may have arisen in response to extinction events. They
allow nature to adapt to high stress situations and readapt
more quickly to emptied niches.
>
> I find myself leaning towards the view that we simply got very,
> very lucky. Life's survival on earth was an incredible fluke, a one
> in a trillion chance. Most planets kill off their life before it gets
> this far.
They don't say that in Rare Earth. They say that primitive life
is likely to be very abundant. The evidence would seem to suggest
that life keeps getting knocked down to its knees over and over
again. But to my mind, that is just a recipe for nature developing
the genetics that let it climb back up faster and faster after
each knock-down. Once you develop a machine that is useful
(be it antifreeze proteins, crocodillins, reverse transcriptase,
etc.) unless you entirely wipe out the phyla it is going to
around for use during the next climb out of the pit.
Rare Earth cites 5 major extinction events since the Cambrian breakout.
Only one, the C/T meteor/comet can be pinned on astrophenomena.
They also say that estimates for planet sterilization events
have been estimated at 1 in 2 billion years. So we may be overdue.
Conversely 2 billion years seems to be more than enough to be enough
time to evolve from bacteria to intelligent life.
Interestingly they point out that events like the Tunguska event
in Siberia in 1908 may occur roughly every century. So if we
solve the longevity problem and get average spans of 2000 years
you have a significant probability of living to see one of these
in relatively close proximity. Now if they can only get them
timed for 4th of July, that would be really cool.
Robert
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