FYI: YAGF: Re: Why We Might be One of Very Few Evolved Races (fwd)

Eugene Leitl (
Sat, 30 Nov 1996 19:29:15 +0100 (MET)

The guys on Great Filters....

---------- Forwarded message ----------
Date: 14 NOV 1996 02:52:30 GMT
From: Frank Crary <fcrary@rintintin.Colorado.EDU>
Subject: Re: Why We Might be One of Very Few Evolved Races

In article <55rt2t$>, Olaf Henny <olafh@Direct.CA> wrote:
>It is widely theorized, that the end o the dinosaur approx. 65
>million years ago was caused by a dramatic climatic change, which
>in turn was caused by a meteor impacting on Earth. From this one
>single historic event we may assume, that an impact of a meteor
>capable of destroying a whole bio-system, might have an average
>return period of somewhere between 10^6 and 10^7 years.

I think you mean 10^7 to 10^8, making 65 million years a
reasonable interval between such events.

>that we reside in relatively quiet outskirts of our galactic arm,
>could it not be that our location is exceptionally conducive to
>the development of a civilization.
>Based on my blithe ignorance in matters of astronomy, I conjecture
>anyway, that as you advance more toward the relatively crowded
>galactic core, the proximity of stellar systems to each other causes
>greater gravitational turbulence within the systems, thereby tearing
>lose more debris, leading to more intensive bombardment of any
>planets, which would otherwise have the potential of providing an
>environment for the evolvement of a sapient race.

That's a very interesting point, and probably correct. The flux
of comets reaching the inner solar system (and therefore the
frequency of K-T events) is strongly affected by the rate at
which other stars pass within ~100,000 AU of the Sun. That's
expected to be in the 10^7 to 10^8 range for the solar system.
This rate would certainly be much higher, perhaps a couple
of orders of magnitude higher, closer to the galactic core.
But I'm not sure how this would affect evolution. Mass extinctions
every few million years, rather than every ~50 million years,
might help intelligent life to evolve. A million years is
long enough to allow intelligent life to evolve. Frequent
mass extinctions might mean more frequent opportunities for
a species to evolve in different ways. Also, frequent perturbations
to cometary orbits might remove most of the existing comets
around a star, over the course of billions of years. So,
although the flux of comets would be high at first, for a
star closer to the galactic core, there is no assurance
that it would remain high.

Frank Crary
CU Boulder