From: Sean Morgan (sean@aurex.com)
Date: Tue Sep 03 1996 - 21:32:06 MDT
Eric Watt Forste writes:
> I'm content, for the time being, to identify the jump from prokaryote
> to eukaryote as the Great Filter.
The jumps seem to be Prokarya to Archaea to Eukarya.
http://whyfiles.news.wisc.edu/022critters/archaea.html
http://cnn.com/TECH/9608/23/science.life/index.html
http://www.reston.com/astro/extreme.html
http://www.lucifer.com/~sean/BT/13.html#Archaea
hanson@dosh.hum.caltech.edu (Robin Hanson) wrote:
>John K Clark writes:
>>Best estimate I've seen is that Eukaryotic cells evolved between 1.2 an 1.4
>>billion years ago, well over 2 billion years after the first life. Well OK, I
>>remember reading a report somewhere about 1.6 billion, but I don't think
>>that's generally accepted.
>
>My sources are pretty authoritive (see paper cites), and clearly say
>that Eukaryotic cells appeared about 1.8-2.0 bya (billion years ago),
>when the atmosphere became oxygen-dominated after all the ocean's iron
>was finally oxidized. (Thus this was probably not a hard step.) Such
>cells became lots more common though about 1.1 bya, apparently with
>the invention of sex (a good hard step candidate).
John K Clark may refer to the controversial work of Russel Doolittle, UCSD
(I'm getting this from _Discover_, June 1996, p.37, so add grains of salt to
taste). He proposed a new clock based on the mutation rates of enzymes,
using the same reasoning as RNA mutation rates. He extrapolated three times
beyond the fossil record (so add more salt). Anyway, his timeline was:
2.0 GY ago -- prokarya
1.8 -- archaea
1.2 -- eukarya
-------------------------------+--------------------------------------------
Sean Morgan (sean@lucifer.com) | All progress is based upon a universal
| innate desire on the part of every organism
http://www.lucifer.com/~sean/ | to live beyond its income. -- Samuel Butler
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