Geraard Spergen wrote:

wrote:

Geraard Spergen wrote:


C12 is 99% of all carbon, C13 is 1%, and C14 is about 1 part per
10^12.

Plants naturally have more C13 than animals so any substance
(including testosterone) produced from plants will have a higher C13
proportion than the same substance produced by animals.


Nice explanation.


Hard to believe there's
any difference in chemical reactions, it's probably due to
photosynthesis.


Um, isn't photosynthesis a chemical reaction? ;-)

Andy Coggan

It's a photo-chemical reaction, maybe instead of "probably" I should
have said "my wild-ass guess"


Fractionation also occurs in non-photochemical processes such as bacterial
respiration in deep smoker vents. It's more related to the difference in
diffusivity of CO2 (or bicarbonate) containing heavier carbon isotopes, the
heavier things move around slower. You also get fractionation in
exchange of CO2 across the air-sea boundary (a mainly diffusive process)
but not so much in precipitation of carbonate, where diffusion is not so
important.

--
Bill Asher