The fossil of a child's tooth is the earliest known evidence of modern humans in western Europe, researchers say.

The discovery of the molar was made in a cave, known as Grotte Mandrin, in France's Rhone Valley.

Researchers say the area also documents the first clear alternating occupation of a site by Neanderthals and early modern humans (Homo sapiens).

Apart from a possible indication in Greece during the Middle Pleistocene, approximately 760,000 to 126,000 years ago, the first settlements of modern humans in Europe have been constrained to around 45,000-43,000 years ago.

But the new evidence - the fossil of an upper molar from a modern human baby - pushes this date back by about 10,000 years, scientists say.

"The Mandrin findings document the first clearly demonstrable alternating occupation of a site by Neanderthals and modern humans," Professor Chris Stringer, research leader in human evolution at the Natural History Museum in London said.

"We've often thought that the arrival of modern humans in Europe led to the pretty rapid demise of Neanderthals, but this new evidence suggests that both the appearance of modern humans in Europe and disappearance of Neanderthals is much more complex than that."

Dental remains from the cave represent at least seven individuals, with researchers identifying six as Neanderthal.

However, sandwiched between the Neanderthal layers was a layer including a fossil molar from a modern human child.

As well as the human molar, researchers discovered stone tools from the unique Neronian industry found in the Rhone Valley.

The industry has previously been regarded as a technological anomaly due to its distinctive features and the fact it had been found in between classic Neanderthal Mousterian layers.

However, in Grotte Mandrin, the presence of the modern human molar in the Neronian layer led researchers to directly link this stone tool industry with Homo sapiens for the first time.

Modern humans have been documented in the Levantine area around 54,000 years ago, but before this study there remained a gap of about 10,000 years before records appeared in Europe at sites in the Czech Republic and Bulgaria.

According to the researchers, the finds from Grotte Mandrin suggest the Mediterranean basin played a major role in the geographic expansion of modern humans into western Eurasia.

"The findings from Mandrin are really exciting and are another piece in the puzzle of how and when modern humans arrived in Europe," Prof Stringer said.

"Understanding more about the overlap between modern humans and other hominins in Eurasia is vital to understanding more about their interactions, and how we became the last remaining human species."

The research, published in Science Advances, was led by Centre national de la recherche scientifique researcher Dr Ludovic Slimak of the Universite de Toulouse Jean Jaures, and included Professor Stringer.