Two teeth from a large deer discovered at a prehistoric site in the vicinity of the Serra da Capivara National Park in São Raimundo Nonato, southern Piauí State, will likely add fuel to the debate about the date of modern man’s arrival in the Americas. Two different laboratories independently dated these giant mammal remains, which were found at a depth of slightly over half a meter in the same geological layer of Toca do Serrote das Moendas where human bones were recovered. One tooth was analyzed at the Department of Physics of the Riberão Preto Faculty of Philosophy, Science, and Languages and Literature, which is part of the University of São Paulo (FFCLRP/USP); the other was examined at the Department of Chemistry of Williams College, in Massachusetts. The results of both tests point in the same direction: 29,000 years in the first case and 24,000 in the second. At the Baixada Santista campus of the Federal University of São Paulo (Unifesp), a third group ascertained the age of a concretion, that is, the compact layer rich in carbonates capping the sediments where the animal teeth and human skeleton fragments were found. As expected, the latter test confirmed that the concretion layer was younger than the layer that contained animal remains: the soil sample was 21,000 years old. Equipment purchased with FAPESP funding was used in the two dating measurements performed in Brazil.
With the results of these three tests, the group of researchers believes it has gathered indirect evidence of human presence at least 20,000 years ago in what is today the semiarid Northeast region of Brazil; this is well before the date that traditional archeology posits for the peopling of the Americas. “The three dates line up,” says physicist Oswaldo Baffa, coordinator of the Ribeirão Preto/USP group and one of the study’s authors. “To mitigate any possible criticism, we were careful to have the samples analyzed at three different places, where they worked blind, without knowing exactly what they were analyzing.” The classic view, advocated by US groups, holds that the first Homo sapiens arrived on the continent about 13,000 years ago by crossing the Bering Strait, which separates Asia from Alaska. The conclusions derived from the tests on the material collected in the semiarid Northeast cave were published in an article in the Journal of Human Evolution in December 2014. “There was no collagen that could be used to directly date the human bones from the cave using carbon 14,” says archeologist Niède Guidon, another author of the paper and president of the Museum of the American Man Foundation (Fumdham). “But the results of the dating of the deer teeth and the concretion layer, obtained by three different laboratories, point to very ancient human occupation of the region.” Fumdham manages the park in conjunction with the Chico Mendes Institute for Biodiversity Conservation (ICMBio), a government agency within the Ministry of the Environment.
Guidon and her collaborators have been conducting research in the vicinity of the park—a UNESCO World Heritage site—since the 1970s, especially in the fields of archeology and paleontology. Her team has catalogued 1,400 prehistoric sites in the Capivara mountains, which has the largest concentration in the Americas; 900 of these have rock paintings done thousands of years ago. In addition to human figures, the drawings on the rocks depict animals, including the marsh deer (Blastocerus dichotomus), which is the species whose teeth were found at Toca do Serrote das Moendas. Though there are numerous sites in the semiarid state of Piauí, they have never provided human remains that could be carbon dated, which is the method usually employed to ascertain the age of organic matter (i.e., bones, shells, wood, coal, fabric) from as long ago as 50,000 years and in some cases even 100,000. Collagen, the organic part of the bones that is indispensable to this dating technique, is a protein that is rarely preserved in the skeletons found in this region.
Since it was impossible to determine the age of the bones found at what are potentially the oldest of the Capivara mountain sites, Guidon has almost always had to endeavor to establish an acceptable timeline for the environment where human bone fragments have been dug up and also for the artifacts and remains that may have been produced by human hands. Over the past three decades, she has dated the remains of stone hearths and artifacts attributed to H. sapiens, along with ubiquitous rock paintings, a mark of human presence. Her results, which are still questioned by a good portion of the scientific community, suggest a human presence in the region between 30,000 and 100,000 years ago; the hypothesis is that man arrived this early by way of an Atlantic sea route. The new study at Toca do Serrote das Moendas, a site located about five kilometers from the park, has afforded the archeologist additional data, based on other dating techniques, which can be applied to the controversial puzzle about when man first stepped foot in the Brazilian Northeast and, accordingly, in the Americas.
This prehistoric site holds new potential for analyses. The sizeable cave, which measures 35 meters by 23 meters at its greatest width, has supplied the remains of paleofauna, stone artifacts, ceramic fragments, and parts of three human skeletons, two from children and one from an adult. The two teeth of the marsh deer lay side by side, 35 centimeters away from the fragments of the adult skeleton, located at the same depth. This scenario is an indication—though not irrefutable proof—that man and animal may have co-existed during the same era.
Electron spin resonance (ESR)—also known as electron paramagnetic resonance spectroscopy—was used to date the teeth. The technique measures the amount of ionizing radiation incident on a sample using the spin concentration prompted by energy deposited in the material. “In principle, the older a tooth, the greater the dose deposited in it,” says physicist Angela Kinoshita, of Sacred Heart University (USC) in Bauru, São Paulo, and a post-doctoral researcher at the USP Department of Physics in Ribeirão Preto, who examined one of the teeth using the technique. When dating a sample, in addition to recording the level of radiation stored in the tooth’s enamel and dentine, scientists must take into account the specific conditions at the site where the material for analysis was found (i.e., local levels of radiation emitted by elements such as uranium, thorium, and potassium), along with cosmic radiation.
A different technique was used to date the carbonate-rich concretion layer that practically sealed off the sediment stratum where the teeth and human remains were found: optically stimulated luminescence (OSL). This method measures levels of this kind of light in the quartz crystals of a geological layer. “Theoretically, the more intense the OSL signal, the older the sample,” explains Sonia Tatumi, the Unifesp physicist who analyzed two samples from the concretion layer at Toca do Serrote das Moendas. “Quartz absorbs blue light and emits OSL in the ultraviolet region,” she said. The data derived from a sample taken from the most central portion of the concretion were inconclusive. But examination of a more external piece of the layer provided the results that appear in the scientific article: an age of 21,000 years, with a degree of accuracy of nearly 94%, according to Tatumi.
Advances in electron spin resonance dosimetry, archeological dating and biomaterials characterization (No. 2007/06720-4); Grant mechanism: Regular Grant; Principal investigator: Oswaldo Baffa (USP/Ribeirão Preto); Investment: R$507,101.73 (FAPESP).
KINOSHITA, A. et al. Dating human occupation at Toca do Serrote das Moendas, São Raimundo Nonato, Piauí-Brazil by electron spin resonance and optically stimulated luminescence. Journal of Human Evolution. V. 77, p. 187-95. Dec. 2014.