On Fri, 27 Jul 2007, Siegwolf Rolf wrote:

> Well the process of decomposition is not only performed by beetles and 
> worms, It is mostly the breaking down of chemical bonds and the 
> activities of microorganisms, and their digestion process is enzyme 
> based, with a number of various biochemical processes.

Sorry for the confusion, we informally use "bugs" here to refer to any 
organism micro or macro.

> And as it is, the lighter isotopes form weaker chemical bounds than 
> heavier ones. Ergo the compounds with the heavier isotopes are more 
> stable and it takes more energy to break them down and consequently the 
> breaking down of the compounds with heavier isotopes occurs in a lower 
> rate than for the compounds of with the light elements. Therefore you 
> get "heavier" the more you decay.

If the reaction is completely inorganic and abiogenic I might immediately 
agree with you. But in a biochemical system things are more complicated. 
You may be right that the end result is that the lighter element get 
digested by enzymes more quickly. However, processwise it would be 
interesting in itself for the very reason that the steps are not as simple 
as you describe.

Think of the breakdown of a protein molecule (a macromolecule). When an 
organism digests it, will it really prefer to break up the amino acids 
with the lighter carbon, oxygen or hydrogen isotopes?


> The term     "Rayleigh decomposition"    fits pretty well....
>
> Actually a topic to include in a lecture, especially in the context of 
> soil processes it could make it easier for the students to remember
>
> Rolf
>
> __________________________________
> Dr. Rolf Siegwolf
> Lab for Atmospheric Chemistry
> Stable Isotopes and Ecosystem Fluxes
> Paul Scherrer Institut CH-5232 Villigen PSI
> Switzerland
>
> e-mail: [log in to unmask]
> Phone: +41 56 310 2786
> Fax     : +41 56 310 4525
>
> Website:
> http://isotope.web.psi.ch
> __________________________________
>
>

- Mihali

----
.  Mihali A. Felipe
.  Gerstein Lab : Bioinformatics
.  Yale University Molecular Biophysics and Biochemistry
.  203-432-6337