The date of the first settlement of the Americas remains a contentious subject. Previous claims for very early occupation at Pedra Furada in Brazil were not universally accepted (see Meltzeret al.1994). New work at the rockshelter of Boqueirão da Pedra Furada and at the nearby open-air site of Vale da Pedra Furada have however produced new evidence for human occupation extending back more than 20 000 years. The argument is supported by a series of14C and OSL dates, and by technical analysis of the stone tool assemblage. The authors conclude that the currently accepted narrative of human settlement in South America will have to be re-thought. The article is followed by a series of comments, rounded off by a reply from the authors.

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The archaeological evidence of the Pedra Furada rock-shelter (northeastern Brazil), showing a long sequence of dated layers from 50,000 years b.p., was questioned in a paper presented by Meltzer, Adovasio & Dillehay, who visited the region at the end of 1993, in volume 68 of ANTIQUITY (1994). This paper presents the reply of the team directly involved in the research programme in this key area of American prehistory.

International audienc

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Dois fragmentos de pinturas rupestres pertencentes a dois sítios arqueológicos brasileiros, sendo um no estado do Piauí (Sítio Toca da Extrema II) e outro no estado do Rio Grande do Norte (Sítio arqueológico Xique-Xique), foram analisados por LIBS (espectroscopia de emissão em plasma induzido por laser). Um instrumento construído no laboratório (laser Nd:YAG, 1064 nm, 5,2 ns), contendo um policromador echelle, foi empregado para a aquisição dos espectros. Estudos preliminares envolvendo uma pintura realizada sobre uma tela de madeira contendo diferentes camadas de material foram realizados para determinar a melhor energia do pulso de laser. Para cada fragmento de pintura, foram realizados 8 pulsos sucessivos em 16 locações diferentes, sendo 8 locações sobre a pintura e 8 sobre o substrato. Neste trabalho, foi demonstrado que a utilização de técnicas multivariadas é indispensável devido à grande complexidade dos espectros obtidos durante estudo de profundidade de amostras arqueológicas.Laser-induced breakdown spectroscopy (LIBS) was employed in the study of two fragments of prehistoric rock wall paintings found at two Brazilian sites: in Piauí State (Toca Extrema II) and in Rio Grande do Norte State (Xique-Xique). A time-resolved echelle based LIBS system assembled in the laboratory (laser Nd:YAG, 1064 nm, 5.2 ns) was employed for spectral acquisition. Preliminary depth profile studies were carried out in surrogate samples of a multilayer painting on wood to determine the best energy for the laser pulse. For each fragment of wall painting, the depth profile composition was investigated by firing 8 successive laser shots at each of 16 locations (8 in the area of pigment and 8 in the area of substrate). It is demonstrated in this work that the use of multivariate techniques is compulsory due to the high complexity of the spectral data obtained from depth profile studies of the archaeological samples. Keywords: prehistoric paintings, principal component analysis, LIBS, laser-induced breakdown spectroscopy, depth profile IntroductionLaser-induced breakdown spectroscopy (LIBS) is an attractive technique for archaeological analysis because it is nearly non-destructive and does not require sample preparation. It also provides rapid multi-element analysis, even for the light elements, and the spatial resolution is almost microscopic. Depth profile analysis is possible and the use of portable instrument allows for in situ analysis of large and unmovable samples.1-3 LIBS utilizes a pulsed laser focused on a small spot on the surface of the sample. The high irradiance (energy per area) produces vaporization Borba et al. 959 Vol. 23, No. 5, 2012 of a tiny quantity of the sample constituents and promotes the formation of a plasma of high temperature capable of atomize and/or ionize most of the chemical elements present in the sample, which are excited to higher electronic energy levels. After relaxation (and an initial intense continuous emission), atomic and ionic emissions at specific wavelengths for each element occu...