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Re: Sinosauropteryx filament melanosomes challenged

David Marjanovic <david.marjanovic@gmx.at> wrote:

> Completely wrong.
> The chemosynthesis in question generates ATP (much of which is used to turn
> carbon dioxide into sugar) using the energy that comes from turning sulfide
> into sulfate. That requires hydrogen sulfide and...
> ...oxygen.  Oxygen that comes from higher up in the water column, from 
> photosynthesis.

Actually, certain chemosynthetic microbes can use alternative terminal
electron acceptors beside oxygen.  For example, thioautotrophic
bacteria in which sulfide oxidation is coupled to nitrate reduction.

> Hydrothermal ecosystems are by no means independent of the
> sun. Only their _carbon_ doesn't come from photosynthesis; their energy
> _does_.

Only if the microbes are respiring using oxygen.  As you say above,
their energy comes from reduced sulfur species, like sulfide.  The
identity of the terminal electron acceptor could be something other
than oxygen.

> The animals in hydrothermal ecosystems are ordinary heterotrophic animals
> that eat organic matter and breathe oxygen.

Yes, these critters would be doomed.  As with us, they need oxygen to respire.

But I think we're straying way OT.  I'll stop here.