Un a study carried out by researchers from USP reassessed the age of the archeological site Alice Boer, located in the city of Rio Claro, in the interior of São Paulo. Past excavations established an age of 14,000 years for the site, which would make it older than the Clóvis culture (13,000 years) in North America. Over the years, however, these results have been rejected by the scientific community and this has led researchers to reanalyze the site with new dating techniques. The study concluded that the archaeological material in the region is actually between 8,100 and 6,300 years old.
Between 1961 and 1986, a team from the National Museum of Rio de Janeiro was responsible for excavating the region. The estimated age was 14 thousand years. In addition, alleged artifacts would have been found at deeper levels of the excavation, suggesting a human presence at the site more than 30,000 years ago.
“With criticism from the scientific community, the site has been little mentioned in academic research over the years,” says archaeologist Astolfo Araújo. Then, a group of researchers from the Institute of Biosciences (IB) and the Museum of Archeology and Ethnology (MAE), both from USP, led by him, proposed to study the site from new excavations, dating and analysis of the artifacts. The results of the work were published in the journal PaleoAmerica , under the title The Rise and Fall of Alice Boer: A Reassessment of a Purported Pre-Clovis Site .
“Despite the initial impact of the results pointed out in the 1960s, the mention of the site only decreased over the years, with no concrete reason for that because no other study had reviewed the data obtained at the time. In other words, there was a scientific problem there ”, says Astolfo Araújo to Jornal da USP . It was based on this that the group decided to verify the results with new techniques. “The carbon-14 dating, for example, showed very large variations, the error was more or less a thousand years”, explains the researcher.
The Alice Boer site is located on a sandy terrain of the Cabeça River and was discovered by João Boer, a local who found a series of lithic bifacial tips – chipped stones – in the region. In the 1960s, the group of researchers found part of this material very close to a layer that supposedly dated 30,000 years ago, and so it was concluded that the pieces found were artifacts (objects made or modified by humans in a culture archaeological).
The material was sent to the National Museum, which allowed, in the recent research, João Carlos Moreno de Sousa, one of the researchers involved in the work, to analyze it again. The conclusion was that what was thought to be an artifact was, in fact, a geofact (a piece of rock that was broken or eroded naturally, without human action).
Among all the material found in the alleged 30,000-year-old layer, only one of them was a broken slug – an artifact that is part of the region’s archaeological culture – and it may have undergone bioturbation when the material is pushed deeper into the earth by action biological, such as an armadillo or earthworm, for example.
The rest of the stones were found in a region that used to be the riverbed. “We realized that the place where they were supposed to have found artifacts was the old riverbed. So, obviously, no one would live there ”, says professor Astolfo Araújo, from MAE. He says that when the river started to migrate, the bottom became a beach and sand accumulated in the region.
This means that the chipping identified in the stones that, in theory, dated 30 thousand years ago was natural. Two factors allowed the realization that it was not the result of human activity: the river chandelier (the so-called patina) and the very distant time between two chipping. “It was possible to identify that there was no anthropic action [ by the human being ] because the material had the so-called river luster, that is, over time, the water polished it and left a glossy aspect”, clarifies João Carlos.
In addition, it is possible to identify that a part of the chipping took place in a very different time span than the others. “We were able to notice that one part of the splinter came out much earlier than the other, you can see the difference for many years. In other words, it was not a human being responsible for the chipping, because, if so, he would not have removed a splinter on one side and waited long years to remove another on the opposite side.
At the Alice Boer site, the actual artifacts found date from 8 to 6 thousand years ago. There, there is a type of tip (produced by chipping stones) that is very specific to the archaeological sites of this region of São Paulo. The Alice Boer lithic industry may be related to an older chronological band, the Caetetuba (11 thousand years old), given the material-cultural similarity.
Examples of typical artifacts from the Alice Boer site, found during the first excavation: four rod points showing technological and morphological patterns from Rio Grande do Sul and a slug. Credits: Reproduction of the article.
Examples of typical artifacts from the Alice Boer site, found during the first excavation: four rod points showing technological and morphological patterns from Rio Grande do Sul and a slug – Credits: Reproduction of the article
For the new dating, two different methods were used: radiocarbon and luminescence. With the first, the organism’s death event is dated, for this, carbon-14 is used. It is a radioactive isotope that is low in carbon, also known as radiocarbon. The technique is only applicable to organic materials (those that have carbon in their composition).
Carbon-14 is formed continuously in the atmosphere, due to the effect of cosmic ray neutrons on nitrogen-14 atoms. It is rapidly oxidized in the air, forming carbon dioxide, and enters the global carbon cycle (a process that guarantees carbon recycling).
Plants and animals assimilate carbon-14 throughout their lives. When they die, they stop exchanging carbon with the biosphere and the amount of carbon-14 begins to decrease. It is from this that it is possible to date the age of the organism. “We know how long carbon-14 decays, so we notice how much is still in the body and, by means of a rule of 3, we determine its age”, explains Araújo.
Luminescence, in turn, is a completely different method from radiocarbon and is not restricted to organic material only, it measures radioactive accumulation. “The technique measures what was the last exposure to light that a grain of sand suffered.” So, we have crystals like silicon, for example. “They are formed by a package of atoms that form an imperfect crystalline lattice, that is, there is space between the atoms”, says the leader of the study.
The radiation from the environment surpasses this cluster of atoms, leaving behind some electrons, which are trapped there as long as there is no agitation. If there is something that shakes those atoms, they release the electrons – usually, what excites them is light. This means that for electrons to be retained there must be a complete absence of luminosity.
“A grain of sand is always zeroed, whenever the sun rises, even if it has accumulated radiation during the night”, says Araújo. From the moment the sand starts to be buried, solar radiation is not able to release electrons, so they accumulate.
The luminescence method consists of collecting this sample with PVC tubes – so as not to catch light – and exciting it in the laboratory, thus, all trapped electrons are released and this tells a story. The researchers know the amount of radiation annually and this reveals the age of the grain.
Thus, the age determined by the study was between 8,100 and 6,300 years, that is, the place is more recent than the Clóvis culture, in North America.
The results elucidated a problem that had been neglected. In addition, the fact that the artifacts are associated with the Caetetuba culture, also located in the interior of São Paulo, shows that there was an intimate exchange between human beings from both regions. “They were probably populations that exchanged, at the very least, information. But there were probably more intimate exchanges, like language and genetics, ”says Araújo.
Most of the Alice Boer Collection was lost in the fire of the National Museum in 2018. It is possible that part of the collection, transported to France in the 1990s, is still installed at the Muséum National d’Histoire Naturelle, in Paris.
The work of Astolfo Araújo, João Carlos Moreno and collaborators was supported by the National Council for Scientific and Technological Development (CNPq); Coordination for the Improvement of Higher Education Personnel (Capes); and São Paulo State Research Support Foundation (Fapesp).
Universidade de São Paulo