From: mike@fionn.lbl.gov (Michael Helm)
Newsgroups: sci.archaeology
Subject: Re: Carbon 14
Date: 13 Apr 1992 05:18:28 GMT
Organization: N.I.C.E.
Reply-To: mike@fionn.lbl.gov (Michael Helm)
NNTP-Posting-Host: 128.3.128.60

I've been meaning to post this for a while.  Hope you all 
still find this of interest, even tho the thread's a bit stale.

Woody Baker writes:
>It all boils down to faith.  Everything has to be taken by faith,
>even the uniformatarian principle that underlies the theory of ...

>Tom Owens writes (...we have no clear examples of carbon 14 data being
>incorrect...).  

>That of course, calls most c14 dates into question, as we can't
>REALLY know what the c13:c14 ratio was. We have to take it on FAITH.
>It would be most intersting to analyze the air trapped in ICE cores
>to see if the RATIO of C..:C14 has ever changed.  It seems that one

[I've just got to say that I don't have a lot of faith 
that faith is involved in nuclear physics.  Thank you.]

Ok.  Here's an extract from a book about Irish archaeology.
(Michael O'Kelly, "Early Ireland", Cambr 1989)  From App A,
"Radiocarbon Dating".

".... 14C which is constantly produced in the atmosphere out of
Ni, by nuclaer reactions with neutrons in [by] the so-called
cosmic radiation...."

"Calibration

"In the early days of the radiocarbon 'revolution' it was believed
that dates expressed in radiocarbon years were the same as solar
or calendar ones. In the 1960s a series of wood samples of which
the solar or calendar date had been established by tree-ring
analysis (see p 343 [another appendix discusses this technique
& what has been done in Ireland & other places, with references])
were submitted for radiometric determination & it was found that
as a rule there was little or no parity between them, particularly
for dates earlier than the 2nd millenium BC.  The tendency was for
the 14C dates to be too young (recent).  A calibration table
based on tree-ring (dendrochronologic) sequence is therefore necessary
in order to obtain the approximate equivalent in calendar years.

"As a very ruf-and-ready rule of thumb it may be said that uncalibrated
dates in the 1st half of the 3rd millenium BP are too recent by 100-200
years;  in the 4th millenium BP by 200-500+ years;  & in the 5th
millenium BP by 500-800 years (Burgess 1980,18). "

Burgess, CB 1980 _The Age of Stonehenge_ London
Bailie, MGL 1985 "Irish dendrochronology & radiocarbon calibration", UJA 48,
   11-23
Pearson &al 1986 "High Precision 14C measurement of Irish Oak to show
   the natural 14C variations from AD 1840 - 5210 BC" Radiocarbon 28, 911-34

Harbison in "Pre Christian Ireland" (p 10) says that the Belfast laboratory
(see Baillie) has shown that 14C dates falling between 800-400bc can
no longer be trusted, bedause they can't be distinguished from each
other.  I have seen a picture of the calibration curve of 14C &
it happens that it is not monotonic during that period!  I don't
have a ref for it but I would guess looking for Baillie citations
mite fetch it up for you.  Now I knew that the modern era could
not be 14C dated -- side effect of nuclear testing -- but this is
the 1st I'd heard that bumps like this existed in the past.