From: "Karen Steelman"
<steelman@...>
To: ROCK-ART@...


Hello List,

Sorry, I forgot that I can't do attachments. I copied
this from the
word
document we submitted to the journal. There may be a
few minor changes
that
were made in the proofs. But, it is essentially the
same as what will
be
published. I will follow this with an email with a
list of the
radiocarbon
dates in "Figure 1".

Regards,
Karen



Comment on “Some Evidence of a Date of First Humans to
Arrive in
Brazil”

Marvin W. Rowe and Karen L. Steelman
Department of Chemistry, Texas A&M University, College
Station, TX
77843,
USA

____________________________________________________________________________
__


Abstract

Watanabe et al. (2003) reported extremely interesting
dates on a
calcite
layer covering a pictograph at the Toca da Bastiana
rock shelter within
the
Serra da Capivara National Park, Piaui, Brazil.
Thermoluminescence and
electron paramagnetic resonance ages indicate that
humans were present
in
Brazil prior to 35 ky ago. We report radiocarbon dates
for rock
paintings at
the same rock shelter and other nearby shelters that
contradict
Watanabe et
al.’s results.

Keywords: First Americans; radiocarbon dating;
calcium oxalate; Toca
da
Bastiana, Piauí, Brazil; rock art
____________________________________________________________________________
__

1. Introduction
Watanabe et al. [14] reported exciting
thermoluminescence (TL) and
electron
paramagnetic resonance (EPR) dates on a calcite layer
deposited over a
red
pictograph at the Toca da Bastiana rock shelter within
the Serra da
Capivara
National Park in Piaui, Brazil. The ages determined
for the calcite, if
substantiated, would provide striking proof of human
occupation in the
area
very early, before 35 ky ago.

The Serra da Capivara National Park and surrounding
areas in Piaui,
Brazil,
are of particular archaeological interest. Niéde
Guidon and her
colleagues
have presented considerable evidence of human
occupation at Pedra
Furada as
far back as 48 ky ago [4,5,7]. Pigments and rock
fragments with rock
paintings have been found in excavated levels at Pedra
Furada that date
to
almost 30 ky ago [3,8]. However, controversy surrounds
the validity of
such
an early human presence in Brazil [6].
We summarize here our dating study of rock paintings
within the Toca da
Bastiana shelter and other nearby rock shelters [12;
new dates
presented
here]. First, we dated organic material extracted from
paint samples
using
plasma-chemical extraction and AMS radiocarbon
measurement. Paint
samples
were collected from (1) the red painting covered by
the calcite
accretion
dated by Watanabe et al. [14], (2) four other
paintings from Toca da
Bastiana shelter (each within 2 m of the calcite-dated
image), and (3)
four
paintings from other rock shelters in the area. Some
dated paintings
were
made with charcoal and others had red ocher
pigmentation.

Secondly, we identified the presence of calcium
oxalate in the calcite
accretion layer using Fourier transform infrared
spectroscopy and X-ray
diffraction. Unlike calcite, calcium oxalate is
thought to form from
ambient
carbon [2,10,11,15,16] It is therefore possible to
radiocarbon date the
“time” of its deposition, essentially the same event
dated by EPR and
TL for
the calcite, assuming that their formation was
simultaneous. Dating
oxalate
provides a good comparison for EPR and TL dates
because the assumptions
and
conditions involved in radiocarbon dating are very
different from those
of
ESR and TL; the latter two are based on similar
assumptions and
conditions.

2. Results

Unfortunately, our results uniformly argue against an
extreme antiquity
of
35 ka or more for the pictographs at Toca da Bastiana.
Figure 1
summarizes
our radiocarbon dates. Radiocarbon measurement of
calcium oxalate
extracted
from the calcite layer dated by Watanabe et al. [14]
yielded only 2490
± 30
BP for a minimum age of painting. A ‘direct’
radiocarbon date for the
red
painting associated with the calcite layer was
determined to be 3730 ±
90 BP
using plasma-chemical extraction and AMS radiocarbon
dating. In
addition,
radiocarbon dates on paint from four other images in
the same shelter
were
1880 ± 60, 2280 ± 110, 2970 ± 300, and 3320 ± 50 BP.
Finally, dates on
four
other paintings/pigments from other nearby shelters
yielded ages of
only a
few thousand years: at Toca do Sitio do Meio, 2700 ±
110 BP; at Pedra
Furada, 2120 ± 110 and 3570 ± 50 BP; and at Toca do
Extreme, 1230 ± 50
BP.

3. Discussion

Resolving the discrepancy between our determinations
and those of
Watanabe
et al. [14] may not be easy. We have attempted to
verify the technique
utilized at the Texas A&M University laboratory for
dating pictographs
(e.g., see Fig. 1 and Table 1 in [14]). Although the
plasma-chemical
extraction method has not been verified independently
by other research
groups, we have no compelling reason to doubt our
results. Studies in
southwest Texas suggest that age uncertainty ranges
for rock paintings
are
approximately ± 150-200 years BP. Small sample sizes
for some of these
Brazilian paint samples may in fact result in an
uncertainty as large
as ±
500 years BP, possibly even more. But this would still
not account for
the
order of magnitude difference between our radiocarbon
results and
Watanabe
et al.’s [14] TL and EPR results. While TL and EPR
dating have been
successfully used to date calcite deposits in
stalactites and
stalagmites
[1,9], we suggest that the use of TL and EPR for
dating calcite
deposited in
this arid, open-air shelter may suffer from inadequate
correction for
the
incorporation of undissolved carbonate dust into the
calcite layer as
it
formed. Incorporation of solid carbonate would make
the calcite layer
appear
older than its true deposition time because the
shelter’s limestone
rocks
are millions of years old.

4. Conclusion

Regrettably, since our radiocarbon results strongly
disagree with a >35
ky
age of the calcite accretion obtained by EPR and TL
dating [14], we
question
their results. The EPR and TL ages cannot be used as
conclusive
evidence to
support very early human occupation in Brazil near
Pedra Furada until
this
controversy is resolved. Our results do not negate the
possibility of
human
occupation in the area as early as 35 ky ago; but
those
radiocarbon-dated
paintings surviving on rock shelter walls are not of
that extreme
antiquity.
Once again, and most dramatically, these studies point
to the necessity
of
independent studies in dating rock art.

Acknowledgements

We are grateful to Dr. Niéde Guidon for inviting us to
study this
important
problem. This work was supported by the Fundação Museu
do Homen
Americano,
Brazil. Additional funding was supplied by a Regent’s
Fellowship from
the
Office of the Vice-Provost for Research and a grant
from the Program to
Enhance Scholarly and Creative Activities, Office of
the Vice-President
for
Research, both at Texas A&M University.

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Fig. 1. Radiocarbon results for rock paintings at Toca
do Bastiana and
other
nearby rock shelters. All radiocarbon dates shown here
are at least an
order
of magnitude smaller than the TL and EPR dates.



Karen Steelman
Department of Chemistry
Texas A&M University
P.O. Box 30012
College Station, TX 77843

Lab: (979) 845-2383
Home: (979) 775-4852
Cell: (979) 324-1307