French cave
© CNRS News
Ring-shaped structures made of stalagmites found deep in the Bruniquel cave network, in the Tarn-et-Garonne, are much older than first thought, scientists have said.

They are among the earliest examples of human construction ever found - and were built in the pitch-dark cave by neanderthals, long before homo sapiens reached this part of the world.

Shortly after they were first discovered in 1990, the structures were carbon-dated to about 47,600 years old - already older than even the most ancient cave paintings yet found, and at the limit of carbon-dating reliability.

But a new study, published in the journal Nature, has put the date of construction back to 176,500 years ago.

The stalagmites had been cut to similar lengths and laid out in two oval patterns up to 40cm high. Scientists do not know what purpose the structures could serve.

"Their presence at 336m from the entrance of the cave indicates that humans from this period had already mastered the underground environment, which can be considered a major step in human modernity," the article in Nature says.

The study's co-author, Jacques Jaubert, from the University of Bordeaux, said he had ruled out the possibility that these rings, which show traces of fire, could have been made by animals such as bears or wolves, whose bones were found near the entrance of the cave.