Re: History of Carbon 14 Dating
- From: John Stockwell <john.19071969@xxxxxxxxx>
- Date: Fri, 13 Feb 2009 15:53:59 -0800 (PST)
On Feb 13, 1:29 pm, Ray Martinez <pyramid...@xxxxxxxxx> wrote:
On Feb 13, 10:42 am, JohnStockwell<john.19071...@xxxxxxxxx> wrote:
Here is a partial chronology of the
development of the calibration of 14C, which includes consideration
of sources of fluctuations in the background level of 14C.
Much of creationist commentary on the possible errors in 14C is
intended
to portray the scientific community as being either incompetent or
dishonest regarding such issues as the consideration of potential
errors
in radiometric dating methods. Creationists never discuss the fact
that given these analyses, scientists have found ways of identifying
and mitigating the effects of these potential sources of error.
What follows is a summary from chapter 14.1.3, p.364-366 of Dickin
[1995]:
1941 Thellier proposed that Earth's magnetic field experiences
secular variations.
1949 Arnold and Libby publish radiocarbon dates of items of known
age.
1952 Libby publishes first book on radiocarbon dating.
1954 Forbush observed that the 11-year cycle of sunspot activity
was inversely correlated with cosmic-ray intensity.
1955 Suess proposed dilution due to the burning of fossil fuels
for the 2% depletion of 14C activity seen in 20th century wood
compared to 19th century wood.
1956 Elasser, et al. predicted variations in the cosmic ray flux
due to secular variations in Earth's magnetic field.
1958 de Vries found that 17-th century wood had a 2% higher activity
than 19th century wood.
1961 Stuiver used historical records of sunspot activity to calculate
cosmic ray intensity, and hence 14C production for the past 1500
years, and suggesting that the observations of de Vries,
correlated with a sunspot minima.
1965 Stuiver used more detailed records to confirm the correlation of
a sunspot minimum with de Vries observations.
1967 Bucha and Neustupny provided paleomagnetic intensity measurments
that supported the existence of secular variations in the Earth's
magnetic field first proposed by Thellier. They were able to
model the variations of 14C production, and almost exactly match
the deviations between the tree-ring and radiocarbon time scales.
By 1969, it became apparent that calibration of the 14C dating method
was both possible, and required, to make radiocarbon dates
useful for the determination of calendar dates. (See the issues of
the journal ``Radiocarbon'' between 1960 and 1969 for published 14C
date lists.)
Indeed, it is often material from prior to 1969 that creationists
use as ammunition against the 14C dating method.
One useful method of calibrating 14C is dendrochronology, or age
dating
by counting tree rings. The basic idea of calibration is simple. Plot
the true date determined from counting tree rings versus the
radiocarbon
date. The result is a plot that can be used to both determine the
actual original 14C/12C ratios (useful for studies in
paleoclimatology)
and can be used to convert radiocarbon dates of other samples into
calendar dates.
The first use of dendrochronlogy to calibrate 14C was made by
1970 Furgeson used dendrochronology of bristlcode pines to calibrate
radiocarbon dating back to 7484- years b.p. (before the
present).
Through comparison with tree ring dates, the 14C method has
been calibrated back to more than 13,000 years before the present,
1991 Becker, et al publish a stable dendrochronological calibration
of 14C back to 11,000 years before the present using tree rings.
The chronology consists of a 9,928-year absolutely dated
dendrochronological record of Holocene oak (Quercus robur,
Quercus petraea) and a 1,604-year floating Late Glacial and
Early Holocene chronology of pine (Pinus sylvestris) from
subfossil tree remains deposited in alluvial terraces of central
European rivers.
In addition, 14C dating has also been calibrated back to more
than 30,000 years before the present using uranium-thorium (isochron)
dating of corals [Bard, et al, 1990] and [Edwards, et al, 1993].
While it is unlikely that 14C will be useful for objects older
than 50,000 years, owing to the problems of background contamination
[Dickin, 1995] and [Lowe, 1991], there is a more recent paper by
[Kitagawa, H., and van der Plicht, J., 1998] discusses calibration
of 14C dating back to 45,000 b.p. using U-Th dates of glacial lake
varve sediments (periodic sedimentary layers).
References:
Arnold, J. R. and Libby, W. F. (1949) Age determinations by
radiocarbon
content: Checks of samples with known age. Science 110, 678-680.
Bard, E., Hamelin, B., Fairbanks, R.G., and Zinder, A., (1990),
Calibration of the 14C timescale over the past 30,000 years
using mass spectrometric U-Th ages from Barbados corals,
Nature, 345, 405-410.
Becker, B., Kromer, B., and Trimborn P., 1991, A stable-isotope
tree-ring timescale of the Late Glacial/Holocene boundary:
Nature, vol. 353 (17 Oct 1991), 647-649.
Dickin, A. P. (1995), Radiogenic Isotope Geology, Cambridge University
Press.
Dalrymple, G. Brent, (1991), The Age of the Earth. California:
Stanford
University Press, ISBN 0-8047-1569-6.
Edwards, R. L., Beck, J. W., Burr, G. S., Donahue, D. J.,
Chappell, J. M. A., Bloom, E. R. M., Druffel, E. R. M.,
Taylor, F. W., 1993, A large drop in atmospheric 14-C/12-C
and reduced melting in the Younger Dryas*, documented with
230-Th ages in corals: Science, vol. 260 (14 May 1993), 962-967
Furgeson, C. W. (1970), Dendrochronology of bristlecone pines, Pinus
aristata. Establishment of a 7484-year chronology in the
White Mountains of eastern-central California, USA.
In: I. U. Olsson (Ed.), Radiocarbon Variations and
Absolute Chronology, Proc. 12th Nobel Symp. Wiley, pp.
629-40.
Kitagawa, H., and van der Plicht, J., (1998), Atmospheric radiocarbon
calibration to 45,000 yr B.P>: Late glacial fluctuations and
cosmogenic isotope production, Science, v. 279, 20 Feb 1998.
Libby, W. F. (1952) Radiocarbon dating, University of Chicago Press.
Libby, W. F. (1970) Ruminations on radiocarbon dating
In: I. U. Olsson (Ed.), Radiocarbon Variations and
Absolute Chronology, Proc. 12th Nobel Symp. Wiley, pp. 629-40.
Lowe, J. John, ed. (1991) Radiocarbon Dating: Recent Applications and
Future Potential, Quaternary Proceedings, Number 1, 1991,
Published
for the Quaternary Research Association, Wiley.
We know carbon dating is unreliable for the following reason:
When a rare circumstance arises where the age of an ancient material
is already known, that is, when an external accuracy check is
available, carbon dating has failed. This has happened with mummy
linen found in Egyptian tombs. Egyptologists and archaeloogists knew
the age of the material beforehand.
The incident you are referring to occurred sometime in the
late 1950s, long before calibration of radiocarbon dating.
I suggest that you read the references that I posted
if you want to make credible criticisms regarding radiocarbon
dating.
Ray
-John
.
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