[ExI] After the Great Filter

Rafal Smigrodzki rafal.smigrodzki at gmail.com
Tue Dec 15 07:40:54 UTC 2020

A recent article in Communications Earth & Environment:


attempts to model the likelihood of Earth-like planets to remain
continuously habitable for 3 billions of years and comes to the conclusion
that the overall success rate would be very low (0.0145). I have doubts
about the approach, in part because I don't really understand how the
results were generated and I am too lazy to read the Methods section where
the assumptions are explained. Well, actually I skimmed through the methods
and I think one assumption is a major blooper - that 3 By of continuous
habitability are needed for intelligent life to evolve. That really doesn't
make sense. The whole modeling effort seems like trying to squeeze way too
much knowledge out of way too little data. Or maybe I am not sophisticated
to see the general applicability of the method?

Still, the article's conclusion is probably correct - even on planets
blessed with all the right ingredients there is going to be a lot of
instability, due to various instantaneous perturbations (asteroids,
supervolcanism) and the interplay of long-term forcings. We know that
complex life on Earth was reset multiple times, so it's plausible that the
same is happening everywhere. Life-sustaining planets most likely all have
plate tectonics, since this is a very powerful stabilizing mechanism
without which the chemical composition of the atmosphere would almost
certainly degrade continuously until water is lost (Mars) or a runaway
heating occurs (Venus). But plate tectonics implies mantle convection and
convection is likely to produce plumes which trigger supervolcanism. So
every living planet is most likely primed to erase large animals on a
regular basis.

I do not believe that dinosaurs or the theriodonts were in some substantial
way more primitive than modern mammals - most likely they were functionally
equivalent to the bulk of modern mammals and the only reason they did not
give rise to intelligent forms is because they got creamed by climate
perturbations too early.

Intelligence most likely appears randomly with some reasonable probability
once you have large animals running around long enough - but exactly how
long is the average time to first evolved sophont is unclear. Probably not
less than 100 million years (Myr), since there were two epochs on Earth
when large animals evolved uninterrupted, more or less, for similar periods
(the above-mentioned theriodonts and dinosaurs) and still did not manage to
evolve intelligence. If we are a lucky throw of the dice, and the average
time to intelligence is e.g. 500 Myr, then even on lucky planets with all
the right ingredients for life there would never be intelligent life
because random resets due to supervolcanism would happen too frequently.

Too much uncertainty, too little data. Anyway, my guess, which I mentioned
here before, is that Earth already passed through the Great Filters. We are
just a couple of decades away from spreading to other planets. I don't
believe that superintelligent AI is a filter, at least not a filter
preventing intelligence survival - even if all humans perish in the robot
wars, intelligence of the inorganic variety will still survive and spread.

We are on the last millionth part of the last sprint of the longest race in
our galaxy, the race to space-colonizing intelligent life. I sure hope we
don't trip up at the last possible moment.

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