From: allenroy (allenroy@peoplepc.com)
Date: Thu Oct 02 2003 - 20:33:20 EDT
"D. F. Siemens, Jr." wrote:
> I did a quick search by Google on "Carbon 14." First, the ratio of
> radio-carbon in contemporary living things is about 10^-12. This is the
> 100% level, approximately, for there are technicalities to the standard.
> Measurement by the most advanced techniques gets down to a little more
> than 1%, for an age of 40,000 years. Theoretically, the newest techniques
> might get to 60K, but the practitioners say it doesn't work. In other
> words, 0.1% is a full order of magnitude better than the best labs get.
> Do you suppose it's artifactual?
From http://www.icr.org/pubs/imp/imp-364.htm (ICRs Impact #364)
"The AMS (Accelerator Mass Spectrometer) method improved the sensitivity of the
raw measurement of the 14C/12C ratio from approximately 1% of the modern value
to about 0.001%, extending the theoretical range of sensitivity from about
40,000 years to about 90,000 years. The expectation was that this improvement in
precision would make it possible to use this technique to date dramatically
older fossil material.1"
from http://www.talkorigins.org/faqs/c14.html (Talk.Origins Archives and
FAQS)
"Dr. Gove and his colleagues are currently trying to improve AMS technology to
be able to identify certain fossil fuels that have extremely low 14C content.
Current AMS techniques have a 14C/C detection limit of about 10^-15
(corresponding to 60,000 yrs), and Dr. Gove's current research, this year, is
aimed at improving detectability to 10^-18 (110,000 yrs)."
"Their ultimate goal is to reliably measure 14C/C ratios down to the
unbelievably low levels of 10^-22 (180,000 yrs). "
This Talk.origins paper talks about possible in-situ occurrence of 14C due to
several factors and the site ends with:
"So, it looks like in-situ production of new 14C is the best-supported
hypothesis; but research is ongoing, and I look forward to seeing the results of
the Old Carbon Project and new research on the deep subterranean bacteria."
Impact #364 say this about contamination.
"The big surprise, however, was that no fossil material [other than oil] could
be found anywhere that had as little as 0.001% of the modern value! Since most
of the scientists involved assumed the standard geological time scale..., the
obvious explanation for the 14C they were detecting in their samples was
contamination from some source of modern carbon with its high level of 14C.
Therefore they mounted a major campaign to discover and eliminate the sources of
such contamination. Although they identified and corrected a few relatively
minor sources of 14C contamination, there still remained a significant level of
14C—typically about 100 times the ultimate sensitivity of the instrument—in
samples that should have been utterly "14C-dead," including many from the deeper
levels of the fossil-bearing part of the geological record."
Allen
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