Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site utastro.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!ut-sally!utastro!ethan
From: ethan@utastro.UUCP (Ethan Vishniac)
Newsgroups: net.astro
Subject: Re: C14
Message-ID: <450@utastro.UUCP>
Date: Tue, 30-Jul-85 14:04:45 EDT
Article-I.D.: utastro.450
Posted: Tue Jul 30 14:04:45 1985
Date-Received: Thu, 1-Aug-85 20:28:38 EDT
References: <320@utastro.UUCP> <713@lsuc.UUCP> <169@polaris.UUCP> <173@husky.uucp>
Organization: U. Texas, Astronomy, Austin, TX
Lines: 39
>
> The reference to solar activity's role in the formation of
> atmospheric C14 got me thinking about something I've been
> wondering about for a couple of years now. Where do the
> scientists who use radiocarbon dating get their correlation
> between C14 concentrations in the organic material under study
> and the amount of time that has passed since the creature (or
> whatever) died? My understanding is that the C12/C14 ratio in
> an organism approached zero asymptotically with passing time
> (e^-at) following the creature's death, since C14 is no longer
> being moved through the living organism. Where does the initial
> atmospheric C14 concentratio data come from? Simply assuming
> that C14 concentration is constant since the beginning of time
> seems questionable to me, at best. How 'bout it, folks?
>
> Mark A. Johnson -- Eastman Kodak Company -- Information Products
This is not my field, but I think I can handle this one. Initially, that's
just what people did (assume constant C14/C12 in the atmosphere). However,
for a while now people have used a calibration curve obtained by finding
pieces of bristle-cone pine. The layers of the pine give a calibration
curve provided that the specimen can be dated. Living pines take one
back about 4000 years. (The surface is being made now. Count the rings
down to the core and sample the core.) With that calibration curve one
can date dead pines and extend the calibration sequence. I believe
that sequence now goes back about 8000 years. In that time it shows
a lot of small bumps and wiggles, and some large scale trends which
correlate with the paleomagnetic data. It is therefore possible to
crudely correct the C14 date using the paleomagnetic data at even
earlier times. I am under the impression that the people who take
ice cores think they will be able to get a calibrated sequence back
several tens of thousands of years. There was a Sci Am article on
this about 10 years back.
--
"Don't argue with a fool. Ethan Vishniac
Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan
Department of Astronomy
University of Texas