Re: 500 million year old poo and Oxygen

In article <e65lso$6n8$1@xxxxxxxxxxxxxxxxx>, Paul Ciszek wrote:
1) How much free oxygen was needed for the worms to exist in the
first place? I assume that there is a direct relationship between
oxygen in the air and oxygen dissolved in seawater, so how much
would have been in the air back then?

"Worms" covers a very considerable range of possibilities.
Depending on whose count of phyla you use (and I admit that I'm *still*
working my way through Margulis' "Five Kingdoms" book) ... a good dozen
? Some are (presently) restricted to our 20-odd % O2, others are
restricted to low- or very low- oxygen environments (priapulids, off
the top of my head - they're a couple of chapters on from my bookmark
in "5K" <G>). The existence of organisms large enough to produce
millimetric faecal pellets doesn't really say much about oxygen levels
/per se/ - a few % would probably have been sufficient.

2) A sort of related question: They have found another sealed
underground ecosystem, in Israel this time, with bacteria as
the "primary producers". Where do such ecosystems get their
oxygen? So far as I know, photosynthesis is the only autotrophic
process that produces free oxygen.

Yeah, I saw that one going past too. Shades of Movile.
I'm not sure the question is well-formed. Let's see - oxygenic
photosynthesis occurs with water being used as a terminal electron
donor, in a number of bacterial "phyla", but in others it's ammonia
that's the electron donor, in others it's hydrogen sulphide.
I have a suspicion that "primary producers" is being used to
mean the organisms that fix inorganic carbon into organic carbon,
possibly using photosynthesis, or some other chemoautotrophic process
to provide the necessary energy. For example, I *think* that using
nitrate reduction as an energy source to fix carbon, which then is used
to feed organisms that respire oxygen from the same ambient water.

Physiology is complex, and I'm definitely under-educated in
respect of it. And since bacteria use something like 150 basic
physiological schemes to eukaryotes single scheme, then I'm tempted to
give up at the start.

--
Aidan Karley, FGS
Aberdeen, Scotland
Written at Wed, 07 Jun 2006 11:13 +0100, but posted later.

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