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Re: Biological Origin of Earliest Fossils Substantiated



On Sat, 16 Mar 2002 23:23:04  
 David Marjanovic wrote:
>> The evidence of 3.85 billion year old life (if I remember correctly) comes
>from Greenland and only consists of indirect isotope chemistry (no actual
>fossils).
>
>Those from Greenland are 3.8 Ga old. Those from Australia (not the Apex
>Chert) are 3.85 Ga old. Both are isotope affairs.

Interesting.  I can't say that I have heard of the 3.85 billion year old 
layers.  Refs?

>>  C12: C13 ratios played a major role in this.  Because photosynthetic
>organisms (bacteria and plants)
>
>Many other lithotrophs, too (e. g. the symbionts of rift worms); not only
>photosynthesizers take up carbon dioxide. The ratios are evidence for life,
>but not for photosynthesis.

Makes sense.  Everything I've read has shown C12:C13 ratios to be evidence of 
photosynthesis, but certainly lithotrophs would also influence said ratios.  

>> In terms of Sulfur (like the S34 atom David mentioned), different analyses
>using S32:S34 ratios can ascertain what type of life was present when a
>certain sulfite
>
>Sulfate.

D'oh! :-)

>> rock layer was deposited.  Chemoautotrophs (sulfate reducing bacteria)
>
>That's not an equation. All sulfate breathers are chemotrophs, though.

Oh, I wasn't equating them (sorry if it came across that way).  I was precisely 
trying to say that _certain_ chemoautotrophs, in this case sulfate reducing 
bacteria, can influence S32:S34 ratios.  

>> make energy by adding hydrogen to sulfur atoms (usually cut from sulfate
>dissolved in sea water).
>
>Mmm... I'd rather express it that way: They breathe sulfate like others
>breathe oxygen, nitrate... or (the methanogens) carbon dioxide. (To make it
>more complicated, there are also heaps of prokaryotes that can breathe
>thiosulfate, sulfite, and/or elementary sulfur in addition or instead.
>Sulfur breathing -- attaching electrons and protons to it, which liberates
>hydrogen sulfide -- is the last step of sulfate, thiosulfate, and sulfite
>breathing.)

Interesting.

>> Anyway, that's some basic geochemistry.
>
>Microbiogeochemistry, to be exact (the word exists). :-)

Probably only in German :-))

Steve

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