Neanderthals' disappearance from Northwestern Europe occurred much earlier than previously thought, according to new research using modern technology that completely strips skeletal samples of contaminants that are likely the culprits of radiocarbon misdating. 

The Neanderthals are modern humanity's closest extinct relatives, and they lived in ice age Europe, with populations spread widely across the continent. How Neanderthals went extinct remains a mystery, but these findings give anthropologists a better understanding of their last known whereabouts in Northwestern Europe — namely, Belgium, which researchers said is "one of the key regions for studying the Middle to Upper Paleolithic transition."

The study, titled "Reevaluating the timing of Neanderthal disappearance in Northwest Europe," was published March 8 in the Proceedings of the National Academy of Science. 

The researchers took collagen samples from Neanderthal skeletal remains originally found in 1886 in Spy Cave in Belgium. These skeletons are some of the first Neanderthal bones ever discovered, "most of them having been excavated during the 19th century," according to Grégory Abrams, one of the study's authors, a member of the Scladina Cave Archaeological Centre and a faculty member of archaeology at Leiden University. 

While taking collagen samples for radiocarbon dating is a standard technique used to date fossils, the researchers had to use an advanced purification method called liquid chromatography in order to separate the collagen samples from all contaminants. 

Technology capable of executing this pretreatment method has been around for about a decade but is becoming more accessible now, according to the authors. Questions remained on the reliability of the dates produced by fossils at Spy Cave, and so recent efforts have "focused on reassessing the collection of human and faunal material excavated from the site over the last century," according to the study. 

Using liquid chromatography, the researchers found that previous dates produced on Neanderthal remains from Spy Cave were inaccurate by as much as 10,000 years because of unremoved contamination. 

These contaminants come from two main sources: contaminants from the ground that are typically younger than the fossils; and contaminants arising from the actual methods of preservation themselves, including glue prepared from bovine bones used to preserve skeletal remains.

Using this process, the researchers were able to isolate just one molecule — a single amino acid — in order to increase the accuracy of the radiocarbon date read. 

The researchers also took samples from two other Belgian sites with Neanderthal remains: Engis and Fonds-de-Forêt. Using the same purification process on those samples, the researchers found that the Neanderthal remains from all three Belgian sites — Spy Cave, Engis, and Fonds-de-Forêt — produced similar ages, confirming the Spy Cave findings.

Based on these new radiocarbon dates, the authors of the study estimate that the Neanderthals disappeared from Northwestern Europe about 44,200 to 40,600 years ago.

This new discovery highlights the importance of using liquid chromatography to isolate a single molecule for radiocarbon dating in order to ensure that radiocarbon dating is not being affected by contaminants. 

 "We can get more accurate, more precise results in radiocarbon dating if we date specific molecules instead of dating materials," said Thibaut Devièse, one of the study's authors, a member of the Oxford Radiocarbon Accelerator Unit at the University of Oxford and professor at Aix-Marseille University. 

In this case, he said, dating the materials — the collagen — would have provided a less accurate date than the amino acid molecule. 

"When you are dating a material, it is often made of a lot of different molecules, so it's more difficult to know if you still have contamination," Devièse said. "So, many labs are working on developing this method." 

The findings of the study also help to elucidate the European transition from the Neanderthals to Homo sapiens, bringing anthropologists closer to understanding the nexus of the transition. Last month, researchers also revealed that Neanderthals may have moved further south and used more advanced technology than previously believed after examining fossils and tools from what is now the Palestinian West Bank.

Devièse and his colleagues explained that with these new dates, "We can create a new reference to approach the cultural events that happened during this transition between the last Neanderthals and the very first modern humans."

Obtaining these dates is only the first step in understanding the transition, however; the researchers said this work, "is to be continued."

"There are still a lot of questions about what happened around 40,000 years ago," they said. "We resolved the first part of the question by discovering when the Neanderthals disappeared. But there are still questions about the culture and cultural attributions of the Neanderthals and the timing of the arrival of modern humans."

The study "Reevaluating the timing of Neanderthal disappearance in Northwest Europe," published March 8 in the Proceedings of the National Academy of Science was authored by Thibaut Devièse, University of Oxford and Aix-Marseille University; Grégory Abrams, Scladina Cave Archeological Centre and Leiden University; Mateja Hajdinjak, Max Planck Institute for Evolutionary Anthropology; Stéphane Pirson, Agence wallonne du Patrimoine; Isabelle De Groote, Ghent University and Liverpool John Moores University; Kévin Di Modica, Scladina Cave Archaeological Centre; Michel Toussaint, Association Wallonne d'Études Mégalithiques; Valentin Fischer, University of Liège; Dan Comeskey, University of Oxford; Luke Spindler, University of Oxford; Matthias Meyer, Max Planck Institute for Evolutionary Anthropology; Patrick Semal, Royal Belgian Institute of Natural Sciences; and Tom Higham, University of Oxford.