<p>The research appeared in the Proceedings of the National Academy of Sciences and was carried out by a team from Belgium, Britain and Germany.</p><p>Co-lead author Thibaut Deviese from the University of Oxford and Aix-Marseille University told AFP he and colleagues had developed a more robust method to prepare samples, which was better able to exclude contaminants.</p><p>Having a firm idea of when our closest human relatives disappeared is considered a key first step toward understanding more about their nature and capabilities, as well as why they eventually went extinct while our own ancestors prospered.</p><p>The new method still relies on radiocarbon dating, long considered the gold standard of archeological dating, but refines the way specimens are collected.</p><p>All living things absorb carbon from the atmosphere and their food, including the radioactive form carbon-14, which decays over time. </p><p>Since plants and animals stop absorbing carbon-14 when they die, the amount that remains when they are dated tells us how long ago they lived.</p><p>When it comes to bones, scientists extract the part made up of collagen because it is organic.</p><p>"What we have done is to go one step further," said Deviese, since contamination from the burial environment or through glues used for museum work can spoil the sample.</p><p>Instead, the team looked for the building blocks of collagen, molecules called amino acids, and in particular selected specific single amino acids they could be sure were part of the collagen.</p><h1>'Reliable framework'</h1><p>The authors also dated Neanderthal specimens from two additional Belgian sites, Fonds-de-Foret and Engis, finding comparable ages.</p><p>"Dating all these Belgian specimens was very exciting as they played a major role in the understanding and the definition of Neanderthals," said co-lead author Gregory Abrams, of the Scladina Cave Archaeological Centre in Belgium.</p><p>"Almost two centuries after the discovery of the Neanderthal child of Engis, we were able to provide a reliable age."</p><p>Genetic sequencing was meanwhile able to show that a Neanderthal shoulder bone previously dated at 28,000 years ago was heavily contaminated with bovine DNA, suggesting the bone had been preserved with a glue made from cattle bones.</p><p>"Dating is crucial in archaeology. Without a reliable framework of chronology we can't really be confident in understanding the relationships between Neanderthals and Homo sapiens," added co-author Tom Higham of the University of Oxford.</p><p>Certain stone tool use has been attributed to Neanderthals and has been interpreted as a sign of their cognitive evolution, said Deviese.</p><p>But if the timeline for Neanderthals' existence is being pushed back, Deviese added, then Paleolithic industries should be re-examined to determine if they really were the work of the extinct hominid species.</p>
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