Warren Ockrassa wrote:
>
> This raises the question of why it was that life seemed to sit and do
> nothing for a very long time — nearly 3 billion years — before
> exploding into the pre-Cambrian diversity that it held. Mats of algae
> and stews of bacteria seemed to be all that was possible for quite a
> long time indeed.
>
> The secret ingredient appears to have been sex. Asexual reproduction,
> in addition to being rather boring, doesn't introduce anywhere near the
> possibility for diversification of a genome like sex does. So somewhere
> around 700 to 1000 million years ago, life discovered this new way to
> do things, and that seems to have been the real turning point.
>
David Brin on 1999-05-24 said:
Evidence from meteorites is strong
that there was a differentiated body that got broken up ~600 million
years ago, and that that's what many asteroids may be from. If so, you
don't have to drill at all: you just find the right asteroid and harvest
the whole thing.*
* Some suggest this was one of 3 bits of evidence that the
solar system was visited in that time frame. The other two were the
Cambrian "explosion" of life ("somebody flushed a toilet"), and the
claim that the age-distribution of ore-bodies of certain minerals that
might be of interest to advanced civilizations shows a distinct drop for
ages >600 million years.
I also heard another hypothesis that the Cambrian explosion happened
when natural radiation dropped low enough to allow multicellular
beings to survive, but high enough to keep a high mutation rate.
Alberto Monteiro
_______________________________________________
http://www.mccmedia.com/mailman/listinfo/brin-l
