Sun Aug 25 13:08:10 1996

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From: Mike Phillips 
Subject: Re: Carbon dating
Date: Sun, 25 Aug 1996 12:07:12 -0700
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>  From: "Robert B. Waltz" , on 8/25/96 8:49 AM:
  
>  Carbon-14 dating works by taking a sample of a once-living thing and
>  comparing the amounts of C-12, C-13, and C-14. The half-life of
>  C-14 is (I *think* -- this is the part I would have to look up) 1440
>  years. So after 1440 years, the amount of C-14 is exactly what it was
>  when the object died. After 2880 years, it is one-fourth. Etc. To
>  get the *theoretical* carbon date, one just finds the ratio of carbon
>  isotopes, then compares it with a graph of the C-14 decay rate. This
>  part is very easy (a lot easier than measuring the quantities of the
>  isotopes, which requires a very accurate mass spectrometer).
>  
>  Which returns us to the problems: First, C-14 is so rare in nature that
>  it never constitutes more than a fraction of a percent of the total. So
>  even a highly accurate mass spectrometer has about a 5% error (hence the
>  inaccuracy of about a century in the findings). Second, the theoretical
>  scheme doesn't work. I don't know why, and neither does anybody else.
>  All dates have to be adjusted. And until we know *why*, it's hard to
>  be sure that we are perfectly accurate.

	The reason it doesn't work is due to the underlying assumption that
C-12, C-13, and C-14 are deposited, each at their own rate, at constant rates
(unique to each individual isotope) over time.  Hence, the calculations depend
on X amount of C-12 accruing in 100 years, Y amount of C-13 accruing in 100
years, and Z amount of C-14 accruing in 100 years.  Since the ratio would be
constant between C-12, C-13, and C-14, if this assumption was true, and since
only C-14 decays (and the rate of that decay is known) then all the researcher
need do is adjust the amount of C-14 in the sample back to it's "original"
ratio by using the rate of decay, and determining the amount of time that decay
was in process.
	The system fails because C-12, C-13, and C-14 are not deposited at the
same rate in the atmosphere in any given period, i.e., solar flares, floods,
meteor strikes, climactic changes, volcanic activity, plate shifts, etc., all
may effect the rate at which C-12, C-13, and C-14 are 'made', hence
'assimilated', hence, 'occur.'  The underlying assumption of constancy is the
weak link.

-------------
Mike Phillips
mphilli3@indy.tdsnet.com

A word is not a crystal, transparent and unchanging;
it is the skin of living thought and changes from day
to day as does the air around us. - Oliver Wendell Holmes

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