ESR involves the uptake of water-soluable uranium by hydroxyapatite
(found in its 'best' form in teeth), *after* the teeth have been
deposited in archaeological context. Electrons are then trapped in the
tooth enamel. One needs to model (i.e., guess) at the annual rate of
uranium uptake--hence the potential for gross inaccuracy in the final
date. Moreover, there are two different models to choose from, a
"linear" and an "early" model, which give very different values for the
same sample. Another factor, besides the uptake model problem, is that
the deterioration of trapped electrons within the teeth is temperature
dependent--so that one must again guess at how rapidly electrons in your
particular case will deteriorate. Microclimate and microenvironmental
conditions have great potential to ruin you. Finally, since no one
wants to burn up neanderthal or _H.erectus_ teeth to get speculative
dates, researchers generally use mammalian teeth 'found in context' with
the cultural or human remains. Taken as a whole, you've got a lot of
room for error.
Thus, we see _H. erectus_ dates in Java of 1.2 million and 26,000--take
your pick.
Some colleagues and I attempted to date a suspected Pleistocene horse a
couple of years ago using ESR. The horse, recovered from a deeply
buried deposit in Indiana, had been butchered by stone tools. The tooth
was a dead ringer for an _Equus occidentalis_ canine illustrated in
_Pleistocene Mammals of North America_ . Obviously, this would be a
rare find. Unfortunately the best interpretation of the results we
could get was that it was probably less than 20,000, but the error
margins made it impossible to distinguish 10,000 years old from modern.
I'm confident it is a Pleistocene horse (by the time an historic horse
would have been butchered in northern Indiana, it would have been with
steel, rather than with stone tools), but I cannot support my assertions
with ESR data.
Now I'm definitely going back to grading papers....
Bob
--
"Society produces rogues and education makes one rogue cleverer than
another." -- Oscar Wilde
Robert J. Jeske, Ph. D.
Associate Professor
Department of Anthropology
University of Wisconsin-Milwaukee
Milwaukee, WI 53201
414-229-2887 (office)
414-229-2424 (lab)
414-229-5848 (fax)
[log in to unmask]
http://www.uwm.edu/wcb.uwm/schools/532/156/rjeske/rjeske.html
Any opinions expressed here, reasonable or otherwise, are mine. They
do not necessarily represent the views of any organization, particularly
the University of Wisconsin-Milwaukee.
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