[Taxacom] Life's origins (Half life of DNA in ancient ice)

[Ken Kinman]

Dear All,
      The half life of DNA in very old Antarctic ice (of different ages) has 
allowed scientists to calculate the half life of DNA in such ice:  1.1 
million years.  This definitely throws into even more serious doubt the 
suggestions (by NASA scientists and others) that life on Earth was "seeded" 
from other planets by way of meteorites.  It should be noted that: (1) DNA 
would probably be totally useless in even shorter periods of time than this 
half life (sometimes just a single base change can be lethal, much less 50% 
damage); (2) radiation intensity would be more intense in outer space; (3)  
seeding with RNA is even less likely (as it is even more unstable); and (4) 
as I have noted before, any of the damaged nucleic acids that might have 
managed to seed Earth would probably be gobbled up by life forms that had 
already evolved on Earth itself.

      Therefore, it has always seemed to me more parsimonious that life 
evolved in situ on early Earth, and panspermia hypotheses are extremely 
improbable, fanciful science fiction that makes little physico-chemical 
sense.  Anyway, now we just have to convince these scientists (and others) 
that life did not evolve in thermophilic environments.  That's another idea 
that has been spread by certain NASA scientists, and it doesn't make sense 
either.  Darwin's warm little pond might not be correct, and life on Earth 
could have begun in very cold water, but either of those makes far more 
sense than life beginning in extremely hot environments.  In any case, below 
is a link to the news story in Nature concerning the recent paper in 
Proceedings of the National Academy of Sciences on DNA half-life in ice.
    -----Ken Kinman

http://www.nature.com/news/2007/070806/full/070806-4.html

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