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ELECTRONIC
COPY OF THE ORIGINAL
Radiocarbon Laboratory, Department of Anthropology
Institute of Geophysics and Planetary Physics
University of California, Riverside
Riverside, CA 92521
20 December 1999
TO: Dr. Frank McManamon
RE: (1) UCR Kennewick results
(2) responses to your inquiries of 12/7/99
and 12/17/99
Dear Frank:
Attached as a table
are the results of the UCR 14C analysis
of two Kennewick bones compared with our earlier Kennewick results for
comparison.
1. Comments on the UCR 14C
Results: On the basis of their amino acid
carbon contents (AACC) and amino acid profiles, UCR-3806 and 3807 exhibit
much lower collagen (protein) preservation than the earlier Kennewick
bone my lab previously analyzed (UCR-3476). UCR-3806 has totally lost
its collegen-like amino acid pattern. As I reported previously, both
UCR-3806 and UCR-3807 exhibited unusual amounts of effervescence in
acid which is usually an indication of significant amounts of secondary
carbonates and there was unusual difficulty in filtering the hydrolysates.
The AACC that I reported earlier by email has been revised
in light of additional analyses. (As I mentioned to you previously,
we had just received our new HPLC and were still calibrating with standards
when the initial analyses were obtained.) The revised AACC values do
not change the fact that both bones are problematical in terms of their
suitability to yield accurate bone 14C
values due to their degraded biogeochemical condition. Although UCR-3807
turns out to have more protein that I reported earlier (14.3% AACC of
our modern bone standard), the amino acid composition is marginal in
terms of its collagen- or non-collagen like characteristics. On a routine
basis, our criteria for an acceptable bone is at least 5% AACC and where
the bone retains a clear collagen-like amino acid profile. On the basis
of their amino acid profiles, both UCR-3806 and UCR-3807 are classified
as non-collagen.
Because of their biochemically degraded condition, I
report the results of the 14C measurements
in terms of "fraction modern" with the apparent 14C
age cited in footnotes. You will also note that the reported 13C
values of these two samples are not typical of collagen amino acids.
I would interpret that these values reflect primarily a dietary effect--namely
that the individual (assuming that there is only one individual here
represented) subsisted largely on a marine diet (e.g., fish). There
also could be a fractionation factor involved due to the poor protein
preservation. (In the case of UCR-3476, the first Kennewick bone we
ran, we also observed a depressed 13C
value and, making certain assumptions, we calculated a reservoir corrected
age of 7880 (160 BP.)
In summary, UCR-3807 exhibits an younger age offset
of about 3% (about 280 14C years) in
comparison with UCR-3476 while UCR-3806 is very anomalous with respect
to UCR-3476. One interpretation is that the age offsets reflect varying
percentages of more recent and/or modern contamination in both UCR-3806
and UCR-3607, with the percentage contribution of contamination increasing
as a function of the decreasing residual collagen protein content. For
UCR-3807, there is enough residual collagen so that the offset is limited
to a few percent, while for UCR-3806, the very low AACC is reflected
in the much more recent anomalous age.
2. Responses to Questions:
A. Questions of December 7, 1999
(1) First set
- Did any of you observe any structure or other
characteristics of the extracted carbon that indicates it is deteriorated
collagen rather than an intrusive element?
Without sequencing data, it would be difficult to establish definitively
that the amino acids came only from collagen peptides. The observation
that the age offset increases in inverse relationship to the collagen
content in both UCR-3806 and UCR-3607 strongly suggests that there
are exogenous amino acids in these samples. As you know, in bone,
it is usually assumed that the older the inferred 14C
age the more likely that this is closer to the actual age since typically
non-carbonate contamination that has not been sufficiently removed
generally renders samples "too young."
- Did any of you observe any structure or other
characteristics of the extracted carbon that indicates that it is
from a source external to the bone sample?
The SEM images did reveal some microstructures that we could not identify
and thus it is not possible to determine if they were organic in nature.
It was difficult to filter the hydrolysate of both UCR-3806 and UCR-3807
which is rarely a problem with high collagen yield bone such as UCR-3476.
- In your experience, is it invariable/common/rare/impossible
for "old" intrusive carbon to contaminate a bone sample
from a riverine, floodplain, or lower river terrace geomorphologic
context?
It entirely depends on the characteristics of the humic
and other soil organic compounds contained in the soil together with
the nature of the ground water conditions over the time period that
the bone has been exposed to the environment. Also, can it be assumed
that the bone was always buried in the same soil profile? May it have
been exposed and then reburied as some unknown period in the past?
- Are there other structural, physical, chemical,
or visual characteristics of the sample and extracted carbon that
suggest to you that it is uncontaminated?
On the contrary, the chemical state of the amino acid
extract from UCR-3807, and especially that from UCR-3806, in my view,
points strongly to the possibility that it may be contaminated with
exogenous carbon compounds.
- Are there other structural, physical, chemical,
or visual characteristics of the sample and extracted carbon that
suggest to you that it is contaminated? If so, what do you believe
the contaminate is?
As noted in 4, the chemical state of the collagen in
UCR-3807 and especially UCR-3806 raises the strong possibility that
both may be contaminated. Soil humics of various types are the most
obvious candidates.
- In your experience, what magnitude of time span
would be required for the characteristics you observed in the extracted
carbon from these samples to have deteriorated from normal bone collagen?
This is very difficult to determine since there are
many environmental variables that can influence rates of biogeochemical
diagenesis processes in bone structures.
- Before we took the samples from the Kennewick
remains in September, we consulted with experts, including each of
you about the kind of bone to select. Dense bone in weight bearing
areas and mid-shaft were the main suggestions we got and followed.
If we were to take additional samples, is there a way to determine
visually which bones would be rich in collagen? If not visually, what
other means would be needed to detect collagen levels?
Except with highly degraded bone where there is a "chalk-like"
appearance, it is usually difficult to determine which bones have
retained more unaltered collagen on the basis of gross visual appearance.
Some have used responses to ultraviolet to gauge collagen content
but there are a number of variables that interfere with good responses.
(I believe that I suggested previously to you that it would be very
helpful to take very small amounts of bone from 20 different Kennewick
bones and determine their amino acid composition. This would give
you an objective basis on which to gauge differential preservation.)
(2) Second Set
- In your experience is it common or rare for samples
from the same skeleton to display such a range in collagen structure
and content?
Few specific experiments have addressed this directly.
The Haverty skeletons exhibited significant variability in protein
content but, in this case, the analyses were done on different skeletons
that were assumed to have been buried in close spacial and temporal
proximity. (Brooks, S., R. H. Brooks, J. Austin, G. Kennedy, J. R.
Firby, L. A. Payen, C. A. Prior, P. J. Slota, Jr., and R. E. Taylor.
1991. The Haverty Human Skeletons: Morphologial, Depositional and
Geochronological Characteristics. Journal of California and Great
Basin Anthropology 12:60-83.). In cases where different parts
of a skeleton have been subjected to different alternating ground
water/moisture cycle (wet/dry/wet) regimes, there can be significant
differences among the bones. This can occur if different parts of
a skeleton are not being exposed to the same ground water conditions
or has been exposed to different soil types by redeposition.
- Do you have any suggestions that could explain
this difference reasonably?
As noted above, differential ground water cycle (wet/dry/wet)
regimes could explain the difference in the same skeleton. Conditions
would depend on the relationship between the position of different
bones in the skeleton with reference to the soil profile/ground water
regime, i.e., if different bones were exposed to varying soil/ground
water conditions.
B. 12/17/99 Question Set
- Have you or some other expert ever summarized
the characteristics of skeletal remains earlier than 7000 years BP
that have been dated? We are checking articles and books on the subject,
such as articles by Powell and Steele that review early skeletal evidence;
"Brule Woman" article; "Arlington Springs Woman"
info; Windover site burial population; Pyramid Lake and Spirit Cave
mummies; other?
There is an extensive literature on the 14C
dating of bone and the problems of dealing with collagen degraded
bone extending back for several decades. For example, Taylor 1987:
53-61 reviews the research as of the mid-1980s and cites the earlier
literature. Hedges and Law 1989 and Hedges and Van Klinken 1992 are
excellent overviews and present the experiences of the Oxford Laboratory.
Stafford et al. 1988 and 1991 reports extensive and excellent studies
carried out by him at the Carnegie Geophysical Laboratory and at the
University of Arizona. Taylor 1982, 1987b, 1992, 1994 reports some
of the work of my lab. Burkey et al. 1998 reports our work in attempting
to deal with collagen-degraded bone.
All of these studies highlight the significant variability
in the degree to which endogenous carbon-containing fractions in bone
are retained and are, or are not, protected from contamination by
a wide variety of physical and chemical diagenetic mechanisms. It
is widely acknowledged that obtaining accurate 14C
age estimates on bone requires attention to detail in sample preparation
and an appreciation that each bone may present an unique chemical
challenge if the isolation of a fraction that contains only autochthonous
carbon atoms is to be consistently achieved.
It should be reiterated that the biochemical condition
of bone reflects more directly the diagenetic conditions to which
it is exposed--which can be highly variable--so that, in one environment,
7,000, 10,000, or 40,000 year old bones can retain close to 100% of
their in vivo collagen, while in another environment, a 1,000
year old bone may have lost most of its collagen content.
References:
Burky, R. R., D. L. Kirner, R. E. Taylor, P.E. Hare,
and J. R. Southon.
(1998) Radiocarbon Dating of Bone
Using Gamma-Carboxyglutamic Acid and Alpha-Carboxyglycine (Aminomalonate).
Radiocarbon 40:11-20.
Hedges, R. E. M. and I. A. Law.
(1989) The radiocarbon dating of
bone. Applied Geochemistry 4:249-233.
Hedges, R. E. M. and Van Klinken, G. J.
(1992) A review of current approaches
in the pretreatment of bone for radiocarbon dating by AMS. Radiocarbon
34:279-291.
Stafford, T. W., Jr., K. Brendel, and R. C. Duhamel.
(1988) Radiocarbon, 13C
and 15N analysis of fossil bone: Removal
of humates with XAD-2 resin. Geochimica et Cosmochimica Acta
52: 2197-2206.
Stafford, T. W., Jr. P. E. Hare, L. Currie, A. J. T.
Jull and D. J. Donahue.
(1991) Accelerator radiocarbon
dating at the molecular level. Journal of Archaeological Sciences
18:35-72.
Taylor, R. E.
(1982) Problems in the radiocarbon
dating of bone. In Nuclear and Chemical Dating Techniques. L.
A. Currie, ed., pp. 453-473. Washington, D.C.: American Chemical Society.
Taylor, R. E.
(1987a) Radiocarbon Dating:
An Archaeological Perspective. New York: Academic Press.
Taylor, R. E.
(1987b) AMS 14C
Dating of critical bone samples: Proposed protocol and criteria for
evaluation. Nuclear Instruments and Methods in Physics Research
B29:159-163.
Taylor, R. E.
(1992) Radiocarbon Dating of Bone:
Beyond Collagen. In R. E. Taylor, A. Long, and R. Kra, eds. Radiocarbon
After Four Decades: An Interdisciplinary Perspective, pp. 375-402.
New York: Springer-Verlag.
- For these relatively ancient remains (post 7000)
is the collagen and its structure typically deteriorated? Is the amount
of carbon in the bones that is available for
14C dating consistently low, if not
consistently low, what seems to be cause of the variation?
As noted previously, there are many environmental variables
that can influence rates of biogeochemical diagenesis. In most cases,
the most critical variables are probably effective mean annual temperature
and effective moisture. Typically, bone in tropical contexts is rapidly
biochemically and physically degraded. Bone from cold environments,
e.g. arctic or high altitudes and bone from special environments that
excludes water (e.g., La Brea Tar Pits or in desiccated desert caves
or rock shelters) can retain their collagen content for extended periods
of time measured, in some cases, in excess of several tens of thousands
of years.
- Can you point me to any general or summary statements
in your articles or radiocarbon texts and general articles about bone
carbon deterioration over time, any graphs or tables on this?
Please see the comments on question 1 above.
- In the processing of the bone samples has your
lab needed to use all the bone? If so, is this because of the deterioration
of the collagen carbon, if not what factor has required use of most
of the bone?
We used about 20% of the UCR-3807 bone we received
and about 30% of UCR-3806 to obtain our dates. (We will need most
of the remaining bone to undertake the additional studies to determine
the source of the contamination. Please see answer to the next question.)
- Can you explain to me in writing the dating of
additional fractions that you and I have discussed, what do we hope
to learn from this, will it be done with both samples or only the
most deteriorated? How long do you estimate it will take?
As we discussed, I would like to determine, if possible,
where the contamination is coming from. The most likely candidate
is the humic fraction. We wish to do an XAD-extraction and also look
directly at a total humic fraction. It may be necessary to request
additional bone to do these tests, but we will start on the remaining
bone currently in the lab. This may take up to another month to 6
weeks, depending on the problems we encounter.
- What description is available of the first Kennewick
sample from the Benton Co. coroner? What portion of the bone remained
after the sample extraction at UCR?
All we have by way of a description of the first Kennewick
sample is the paperwork that we received from the submitter. Our results
were published in Science. [Taylor, R. E. et al. (1998) Science
280:1171-1172].
I trust these responses and suggestions have been responsive
and helpful. If and when this data is released to the popular press,
I know that you will find some way to get them to report it appropriately.
Regards,
R. E. Taylor
Professor
Director, Radiocarbon Laboratory
| UCR/CAMS
Radiocarbon Analyses of Kennewick Human Bone |
|
Laboratory
Number |
Sample
Designation |
Bone Preservationa |
Fraction measured |
13C
(permil) |
|
Radiocarbon analysis |
| |
|
|
|
|
Fmb |
14C
age (BP) |
|
UCR-3476/
CAMS-29578 |
5th left metacarpal APS-CPS-01 |
68.8%(C) |
total amino acids |
-15.4 |
---- |
8410±60c |
UCR-3807/
CAMS-60684 |
CENWW.97.
R.24(MTa) |
14.3%(NC)d |
total amino acids |
-10.8 |
0.3633±0.0014 |
---e |
UCR-3806/
CAMS-60683 |
CENWW.97.
L.20b-DOI2b |
2.3%(NC)f |
total amino acids |
-10.3 |
0.4216±0.0015 |
---g |
|
aExpressed
as % of amino acid carbon content (AACC) of modern bone standard.
C = collagen-like amino acid composition. NC = non-collagen amino
acid composition.
bFm
= fraction modern where 1.0 = "modern." pM (percent modern)
= Fm x 100.
cConventional radiocarbon age in
14C years BP. Reservoir corrected
age = 7880±160 [Taylor et al. (1998) Science 280:1171-1172]
dRevised AACC after duplicate analysis
and recalibration of HPLC. Initial analysis = 3.2% AACC of modern
bone standard. Gly/Glu ratio and other indices of collagen-like
amino acid profile indicates significant biogeochemical diagenesis
has occurred and on this basis the profile is characterized as non-collagen.
eApparent 14C
age = 8130±40 BP
fRevised AACC after duplicate analysis
and recalibration of HPLC. Initial analysis = 5.3% AACC of modern
bone standard.
gApparent 14C
age = 6940±30 BP
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