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. 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.

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



On 26 Jul 2007, at 22:11, Mihali A. Felipe wrote:

> On Thu, 26 Jul 2007, Siegwolf Rolf wrote:
>
>> you become increasingly "heavier" until there is nothing left of you,
>> sounds paradoxical doesn't it?
>>
>> Rolf
>
> Yes it does.
>
> It's difficult to imagine why the bugs eating you will have a  
> preference for your light isotopes though.
>
>
> - Mihali
>
> ----
> .  Mihali A. Felipe
> .  Gerstein Lab : Bioinformatics
> .  Yale University Molecular Biophysics and Biochemistry
> .  203-432-6337

__________________________________
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
__________________________________