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Re: reply to orion-list Radiocarbon discussion

I would reply to Greg's comments, my interest is in trying to add some insight
from the technical side into the discussion about the DSS datings which have
been done so far.  I replied to an e-mail I was sent and I assumed the remarks
were all Greg's, apparently some were attributed to him,

Greg Doudna wrote:

> > > > > regarded by most as accurate.  The principle is a sound
> > > > > one: in any battery of lab data, data points at one end or
> > > > > the other of distributions _must_ be regarded skeptically.
> >

I would again state, this is for repeat measurements on the same sample.  I am
not disputing that one date or another might be in error, however for 4QpPs(a),
as I recall, all the data were on the "young" side of 0CE.

> I am mystified by Jull's objection to my statement, since my
> understanding is that it is routine in datings of, e.g. items from
> a particular archaeological assemblage, to regard skeptically
> single dates that appear the earliest or latest in a battery.  (If
> requested I can cite cases on this point.)

See above.

> The logic is simply
> that no individual date, even at two-sigma 95% confidence, is
> infallible.  Therefore single dates at one end or another of a
> distribution cannot be granted complete weight in upholding
> major conclusions.

This is quite so.  The more dates, the better one's understanding of the
distribution of results.

> In the case of 4QpPsA, if this carbon
> date is correct there would be evidence (for the first time, in
> my opinion) for a 1st century CE scribal copy of a Qumran
> text.  But--it is at one end of a total distribution now of 19
> Qumran text dates.

That is correct, but this is a different sample than the 18 other texts cited,
all of which have their own distribution of results.  I suppose what you are
saying is that, if we assume all the texts are made about the same time, that
the outliers are the most suspect.  However, one has already made a hypothesis
about the true age and is then applying some statistical or other criterion to
the results, to make such a judgement.

> There are clear grounds to suspect an
> occasional incidence of contamination affecting at least two
> of the 19 AMS datings which _neither_ Zurich's nor
> Tucson's pretreatment procedures were successful in
> removing.

I do not dispute that these results on 4QpPs(a) might be in error, but we have
not yet established why that might be at this point.  Certainly, we have found
no objective reason to reject the dates .

> The fact that the Tucson report found nothing
> unusual about the 4QpPsA sample in terms of visible glue
> contamination does not negate the unfortunate fact: which
> is that no test for contamination, no analysis of runoff, no
> measurements of differently-cleaned samples, etc. was
> done.

As we have discussed, all the samples were looked at under a microscope to look
for "obvious" contamination, like pieces of glue.

> If 2 of the 19 are conceded likely to have had their
> datings affected by contamination, it is not unreasonable
> to ask if there may have been 1 or 2 more.  And if we
> don't know the answer to this, then we don't know.

I can't argue with this statement and the only way we will find out is with more

> In the absence of evidence of non-contamination
> or other corroboration, this single pPsA date is simply a
> black hole, an unknown, an uncertainty--what else can I
> say?  I don't think T. Jull would actually disagree with this
> last sentence.

I don't disagree, but, if you take a completely objective position (i.e. that
you don't have a predisposition to some particular result) then it's hard to see
why one would reject it.

> I have recommended for the next battery
> that further samples from 4QpPsA, and 4QpIsaA and
> 4QpHosA also (believed to be from the same scribe) be
> dated, with procedures designed to eliminate the
> contamination issue and answer this question.  If that
> original Tucson AMS dating for 4QpPsA comes up
> replicated, clean, etc. the question of the existence of
> 1st century CE Qumran copies would be answered: there
> would be a secure basis to know it.

Quite so, replication of results independently is the best solution.

> But there simply is
> not, at this time, a secure basis for knowledge of the
> existence of 1st century CE Qumran text scribal activity
> on the basis of the single existing 4QpPsA radiocarbon
> date, considered in isolation.

It is certainly weak evidence which requires support by further dates from the
same period  to support it.  However, again, we can't just dismiss it at the

> Jull said:
> > All of these samples were papyrus and not parchment.  I think this may be
> > important to understand these differences.
> >
> Can you say what you mean by suggesting that this plays
> a role in explaining the apparent striking Tucson/Zurich
> offset in dating these papyrus fragments from identically-
> dated texts?

It is possible that offsets of about 30yr could be due to some miscalculation of
the corrections for the 13C/12C isotopic compositions of the samples.  (This is
a very technical point on how the results are actually calculated).  However, I
am not sure that the data supports a systematic offset, although I have heard
this discussed before, by Rodley and also by Doudna.

I will try to respond to comments on technical aspects of the radiocarbon dating
from time to time,

Tim Jull

For private reply, e-mail to "A.J.T. Jull" <ajtjull@physics.arizona.edu>
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