I realised I had made a critical error by conflating the rock shelters Toca da Pedra Furada and Toca da Bastiana. It is the latter and not the former under discussion, with both being present and having rock art paintings in the Serra da Capivara National Park. In line with this, I'm posting a revised critique below with my sincere apologies.
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I'd like to make it clear before I begin that my knowledge of the chronology, stratigraphy and indeed the remains found within the Serra da Capivara National Park is not up to standard. I'm having to conduct some background research on the Net, which has obvious limitations in itself. I am interested to a degree in the occupation of the Americas but not to the extent of reading through more than excellent summaries (the conference collection of papers, "The First Americans", plus journal article summaries) and one or two actual site reports (Meadowcraft).
During my search I am across this university
url here which provides a very short summary on Pedra Furada. The first thing which caught my eye was the attribution of the rock art to the "Serra Talhada Phase (6,000 - 10,400 years ago)". Unless two or more periods of rock art painting are proposed for Pedra Furada, this is in contradiction to other information onhand:
"
At the painted rockshelter site of Pedra Furada (Split Rock) in Piaui, the flaked stones, red-stained rock clusters, and charcoal radiocarbon-dated as early as 30,000 yr B.P. (Guidon & Delibrias 1986), appear to be products of natural processes 9Lynch 1990; Meltzer et al. 1994; Roosevelt et al. 1996: 374, 383). A fragment of painted cave wall found with the charcoal could have falled from the wall deep into the soft, indistinct sand strata. All the usual signs of prehistoric human habitation, such as fragments of burned bones and carbonized food plants, were absent from the early strata." (Roosevelt, Douglas & Brown. 2002. Clovis and Pre-Clovis viewed from South America. In, "The First Americans": 189)
I have found some representations of these rock art paintings
url here (watch the pop-ups).
Juha has explained the workings of TL dating satisfactorily and therefore there is no need for me to go over them again. An explanation of EPR (ESR - Electron Spin Resonance) can be
found here. While Juha opted to discuss the TL dating separately, I would like to take a different approach with regards to Watanabe et al.'s article on Toca da Bastiana as I feel my comments can be applied equally to both the TL and ESR dates. This isn't the most convincing article I have read and whilst the resulting dates are suggestive, questions remain in my mind. It's only at the end of the article that we learn that the first calcite sample dated back in 1991 wrought a ESR date of 27kya in terms of that sample deriving from the bottom of the calcite formation. Returning to the actual calcite formation, the authors state, "The remaining part of the same calcite was used in the presented studies..." However, they simply have not made clear whether (a) the entire remainder of the calcite formation was used up in the study (unlikely but not beyond the realm of possibility - the authors should have stated), or (b) where the samples came from in the formation which were tested. The positioning of new samples is significant: if the dates derive from the top of the formation then it adds credence to their later claim that "it is likely that the calcite strip on the painting was not formed at once and the end position dated by Baffa Jr is younger than the remaining part dated in the present work"; if however the dated sample(s) was the remainder of the formation or in the middle or nearer the bottom of the formation, it does raise serious questions regarding the reliability of these dates - no calcite formation is suddenly going to slow its growth to that extent and it also means that the remainder of the formation is left undated. We have one TL date and one ESR date. While they are consistent with each other, the fact remains that they do conflict with the earlier ESR date and it remains that even with such confliction the authors did not undertake other sample testing from different areas in a 40cm long formation. While the authors appear to have dealt with the possibility of radiation and contamination from the actual rock face behind the calcite, this is a rock shelter and has contamination in any form been ruled out from water dripping from the ceiling or contamination via other means - no information is given.
If the two ESR dates are taking as representative of the whole formation, which is effectively the alternative to the two-stage growth process that the authors do not explore, than we end up with a situation in which we have an ESR date of 35kya and another ESR date of 27kya. This raises the question of the tolerance error margins inherent in ESR dating, so I turned to Schwarcz & Grun (1993. ESR dating of the origin of modern man. In, Aitken, Stringer & Mellars "The origin of modern humans and the impact of chronometric dating"). In addition, the following from Schwarcz & Grun is valuable scepticism: "At present, the precision of the ESR ages ranges from 10 to 20% of the age and is largely limited by uncertainties in the estimates of internal and external dose rates." If we were to take a 20% error range and apply that to the Toca da Bastiana ESR dates, we end up with two dates which only overlap at the ends of the error margins. Remember that the authors state "Experimental errors are not included in the Table 1, but an error of about 1550 years is estimated for the TL method. The error is much larger for EPR technique and it is estimated to be about 5000 years."
I would like to know where the old date for the rock art of c. 6000 - 10400 BP came from at Pedra Furada and if this is part of the standard literature on the site, if the rock art is directly compatible with that from Toca da Bastiana and if they are similar then the question becomes why wasn't this discrepancy directly addressed by Watanabe et al. within their article (Some evidence of a date of first humans to arrive in Brazil. JAS, March 2003).
In my mind, problems remain unaddressed which frankly should have been dealt with within this article. I am looking forward to future critiques of this work by scholars who are more familiar than myself with the site. Presently, I would rate these datings of the rock art as possible but far from proven.
My concerns regarding the level of detail within this article is compounded by their two final paragraphs which state: "Neves & Pucciarelli (1991) and Neves et al. (1999) analysed a female skull found at Lapa Vermelha
archaeological site in Minas Gerais State, Brazil and concluded that it has Negroid characteristics. It is
commonly accepted that the ancestors of North and South American Indians are of mongoloid type. Similar findings were reported concerning human skulls found in Kennewick and Spirit Cave in the United States.
"Although little probable, the possibility of migration from Australia and surrounding islands across the
Pacific Ocean or from Africa across the South Atlantic Ocean, more than 50 ka years ago, cannot be
discarded."
The two references given for Neves are:
Neves, W. A. & Pucciarelli, H. M. (1991). Morphological a?nities of
the first Americans: an exploratory analysis based on early South
American human remains. J. Hum. Evolution 21, 261?273.
Neves, W. A., Powell, J. F. & Ozolins, E. G. (1999). Modern human
origins as seen from the peripheres. J. Hum. Evolution 37, 129?133.
The female skull mentioned is Hominid 1 at Lapa Vermelha IV. I have another article which analyses this remain:
Walter A. Neves, Joseph F. Powell, Andre Prous, Erik G. Ozolins and Max Blum. LAPA VERMELHA IV HOMINID 1: MORPHOLOGICAL AFFINITIES OF THE EARLIEST KNOWN AMERICAN. Morphological Genetics and Molecular Biology, 22, 4, 461-469 (1999). They conclude, "Despite the fact that our research, past and present, does not address time of entry, it has significant consequences for the problem of the ancestral populations involved. The results obtained in this work confirm our previous findings that the first Americans have no special biological resemblance to modern northern Asians. As can be seen in Figure 2, the oldest human skeleton of the Americas shows a strong similarity with modern Africans and Australians. When the comparison is made with Late Pleistocene and Early Holocene fossil hominids (Figure 3), the first known American is surrounded by early Australians and Zhoukoudian Upper Cave Hominid 103. There is no necessity of invoking the occurrence of trans-oceanic migrations to explain the pattern of biological affinities we have been finding for the first Americans. The best way of reconciling the pattern of morphological similarities found in this work with common knowledge about human evolution in East Asia is to assume that both the first Australians and the first Americans shared a common ancestral population in mainland Asia. This ancestral population could well be represented by hominids similar to the Zhoukoudian Upper Cave people (Kamminga and Wright, 1988; Wright, 1995; Neves and Pucciarelli, 1998) and its ultimate origin can be traced back to Africa. The idea that East Asia was occupied by an Australian-like population by the end of the Pleistocene has gained more support recently. Matsumura and Zuraina (1999) described a very well-preserved skeleton from Gua Gunung, Malaysia. The specimen is aged 10,200 B.P. and
is said to be a late representative of a non-specialized morphology, similar to Australian Aborigines, in East Asia.
If our inferences are correct, the Americas could ultimately be seen as part of the first expansion of anatomically
modern humans out of Africa, which started during the beginning of the Upper Pleistocene. Recent acceptance of Late Pleistocene dates for the occupation of the site of Monte Verde, Chile (Meltzer et al., 1997), now suggests that populations colonizing the New World may have crossed the Bering Strait earlier than previously
thought. This makes our suggestion still more plausible."
