Re: poly: polymath digest for 18 Jan 98

From: carl feynman <>
Date: Mon Jan 19 1998 - 11:54:31 PST

At 10:48 AM 1/19/98 -0800, David Brin wrote:
>... If
>Earth really does seem to skate the very inner edge of a very broad 'life
>zone' around Sol, that would seem to be a statistical fluke even more
>improbable than our having a very large moon.

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

Warning: this is recollection, not based on looking anything up. I'm at
work and lacking the right sort of reference book.

>(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.

Received on Mon Jan 19 19:57:07 1998

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