> Interesting question though,
> I.e how would you answer this in general?
>
> I know there has been lots of work on
> 'early metabolism'.
>
> I am interested in studying the metabolic
> network to see if it can give us clues
> relating to age of metabolism.

I wonder if you could expand on this interesting idea -- would the null
hypothesis here be something like 'the most metabolically connected
compounds/chemicals are the oldest'?

> Could we make a chemical phylogeny with
> dates and branch points?

Phylogenies and cladograms are fairly routine to make, given you have some
well grounded way to measure the similarities and/or differences in what
you're interested in.  Certainly this has been done for metabolic enzymes
(i.e. phylogenies of the corresponding protein sequences), but I'm not sure
I've ever seen an incarnation of this for the chemicals themselves... sounds
pretty cool though.

[I suppose one problem is how early you want your dates to go; certainly
genomics has given some idea of what was going on in the last common
ancestor of all modern life, but the problem is it's not really all that
different (based on our extrapolations) than a modern bacterium -- e.g.
DNA->RNA->protein information flow was certainly present, it had ATP
synthesis driven by proton translocation across a membrane, etc.  While this
is really interesting in and of itself, that last common ancestor still
emerges from an obfuscated black box (representing for example the RNA
world, primitive liposomes, and so forth).]
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