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Archaeological dating Retracing time.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 68:555 (1985)
Film Review
Archaeological Dating: Retracing Time
JEANNE E. ARNOLD
Department ofSociology and Anthropology, University of Northern Iowa,
Cedar Falls, Iowa 50614
Encyclopedia Britannica Educational Corporation, 425 Michigan
Ave., Chicago, Illinois 60611, 1976. 16 mm color sound film, $315;
video cassette, $250; rental, $13.90. 18 minutes.
A variety of archaeological dating techniques commonly applied in North America
and particularly in the American southwest
are introduced in this film, beginning with
the examination of different classes of materials that may lend themselves to relative
chronological dating (ceramics and stone
tools) and progressing to absolute dating
techniques such as dendrochronology, archaeomagnetism, obsidian hydration, and
radiocarbon dating.
The principles of relative dating and stratigraphic analysis are introduced by Cynthia
Irwin-Williams as she excavates at the prehistoric Salmon Ruin in New Mexico. IrwinWilliams identifies various materials recovered from a kiva within the ruin and
shows how it and other structures may be
relatively dated using such materials. In one
instance, firm contemporaneity between a
living floor within the ruin and part of the
prehistoric sequence representing the Anasazi at Mesa Verde, Colorado, is established
through pottery analysis.
Next, the high-precision dendrochronological dating technique is explained. Dendrochronology has made possible the dating of
many prehistoric structures in the southwest
t o the exact year of construction. A dendrochronological sequence has been compiled
using successively older wooden beams t o
create a master tree-ring chart which is accurate to the year, extending back to 59 BC.
This important dating method is clearly illustrated and several of its various applications are introduced. Archaeomagnetic dating of baked clay hearths is also illustrated
briefly, as is the technique of obsidian hydration dating. The limitations of these two
techniques are not discussed, perhaps to
maximize the clarity of the presentation by
reducing some of the real-world complexities,
0 1985 ALAN R. LISS. INC
but it seems prudent nevertheless to alert
viewers to certain difficulties in interpretation and potential margins of error in such
approaches. To some degree this issue resurfaces in the film’s discussion of the most
widely applied of all absolute dating techniques, radiocarbon dating. This method is
described in a manner that emphasizes the
laboratory processing of the organic sample
and the apparatus used in measuring Carbon-14. More could be said about the fundamental reasons the radiocarbon technique
works and, again, some of the problems we
have with dates obtained by this method.
In spite of this minor philosophical difference about what ought and ought not be
mentioned in the educational presentation of
dating methods, 1 recommend this film very
highly. It is clear, superbly photographed and
edited, and the package presented to the
viewer is a satisfying one. The various materials from the Salmon Ruin provide an AD
1061 tree-ring date, an AD 1095 archaeomagnetic date, an AD 1095 obsidian hydration
date, and an AD 1100 (+70) radiocarbon date.
The high quality of the archaeological fieldwork conducted by Irwin-Williams is evident
and her dedication and that of her crew to
careful analysis of materials from this site
provide an excellent model for beginning students. In particular, high school students and
university students in introductory physical
anthropology and archaeology classes will
find this film useful and interesting. In some
cases, instructors might choose to supplement a showing of the film before or after
with remarks on difficulties and limitations
of dating techniques. Instructors of advanced
students of archaeology may find the introductory nature of the film to be inappropriate
for their classes.
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