Re: poly: polymath digest for 19 Jan 98

From: d.brin <>
Date: Tue Jan 20 1998 - 16:38:46 PST

Carl Feynman wrote: >>The Sun has been getting slowly brighter. My
understanding is that the
earth got about 25% less sunlight 4.5 billion years ago, and was then near
the *outside* of the zone where liquid water was possible, even with a more
CO2-rich atmosphere. So it might be that in order for a planet to have
oceans for a substantial period of time, it needs to be in just the right place.

DB: If Earth were at the outer edge of the life zone, it would presumably
have had a Gaia equilibrium with heaps of CO2... which is exactly what was
the case in the proterozoic. Still, I have trouble believing it really was
at the outer edge, since the transformation to low CO2 was non-linear. It
happened pretty rapidly. The suddenness might have tipped Earth into a
total ice age if Earth had really been toward the outer edge. Still Carl
raises a good point

> >(Having a large moon has
> >sometimes been cited as a 'reason' for Earth to be fecund.)
> By whom, and on what grounds? I read this in a Larry Niven story years
> ago, but I don't recall seeing it anywhere more authoritative.

Damien replied: >>Asimov, on the grounds that it caused there to be more
elements in the crust, leading to a higher mutation rate. (Spacer Robots
Empire Foundation universe.) And I've heard of the moon sucking off
atmosphere, to avoid being like Venus. (Was that Niven?) I've also
heard that the latter is discredited.

DB: Asimov said this in Robots and Empire, which is the central book of
the entire series, because it sets up his entire premise for why the
Foundation Universe is the way it is. (In that book, two robots deliberate
human destiny without even once consulting a single wise human being.) Of
course, next month I start writing THE SECRET FOUNDATION, which is vol 3 of
the new foundation trilogy (vols 1&2 by Benford and Bear are already out).
In that book I plan on 'dealing with' the idea that you can only get
mutations that way. (There are lots of other ways.)

Good point about uranium oxid floating!

Received on Wed Jan 21 00:34:52 1998

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