RE: Radiometric Dating Techniques

Vandergraaf, Chuck (vandergraaft@AECL.CA)
Tue, 10 Feb 1998 14:42:39 -0500

Chris & Burgy,

Thanks for your comments. For reasons I don't quite understand, the
flow of ASA-generated e-mail stopped overnight and has just now started
again, so I don't know who else beside you two have commented on my
(hastily) composed e-mail.

Chris writes, "Minor technical nit: Wood dates to the year when
it *grew*, not
> necessarily the year it was cut."
Chris, yes, you are correct, of course. The C-14 uptake stops when the
photosynthesis process ceases to bring fixed C-14 into parts of the tree
that are not biologically active anymore. However, most tress (except
Sequoias and bristlecone pine trees, if I remember correctly) don't last
all that long and the error of the C-14 measurement is probably greater
than the lifetime of the tree. One can also cite an isotope effect in
photosynthesis and argue that the kinetics of C-14 reactions are a bit
slower than chemical reactions with C-12 but remember, the initial query
came from a high school student.

In reply to Burgy that "nobody knows how much C-14 a tree had 5730 years
ago," Chris's comment is correct. Again, I believe that the
bristlecone pine tree was used to "calibrate" the system.

BTW, tree rings hold all sorts of interesting information. One of my
fellow PhD students at Penn State went on to do a post doc research
project where he looked at trace element concentrations in tree rings
and was able, by counting backwards, to correlate these concentrations
with known natural an industrial events. But I digress.

Interestingly, I am just now preparing a lecture on the age of the earth
and geochronology to students in a class I teach at a nearby Bible
college. The student body contains a considerable fraction of YEC's (or
at least adhere to a literal interpretation of the Genesis account of

On a related topic, is there a YEC explanation for the Oklo phenomenon?
I'm curious.

Chuck Vandergraaf