Slowly but surely, the mysterious and haunting Chauvet cave is giving up its secrets.
The cave, declared a UNESCO World Heritage site two years ago, was discovered in the south of France in 1994. Before the three amateur spelunkers found the cave in December that year, scientists believed, no human had stepped foot inside for more than 27,000 years.
Studies have shown that many of the ancient and beautifully preserved prehistoric paintings of horses, cave lions and rhinoceros on the cave's walls were made more than 30,000 years ago, making them some of the oldest known artworks on the planet.
Now, scientists have assembled more than 250 radiocarbon dates made from rock art samples, animal bones and the remains of charcoal used by humans scattered on the ground to create the most accurate timeline yet of who used the cave and when.
The new work, published Monday in the Proceedings of the National Academy of Sciences, finds that humans frequented the cave during two distinct periods that were separated by several thousands of years.
The newly synthesized data suggest the first period of human occupation lasted from 37,000 to 33,500 years ago. The second prehistoric occupation began 31,000 to 28,000 years ago and lasted for 2,000 to 3,000 years, the researchers wrote.
People never lived in the cave, explained Anita Quiles of the French Institute of Oriental Archeology and Jean-Michel Geneste of the Ministry of Culture and Communication in Paris, two of the authors on the paper. It appears they went there mostly to create their symbolic art.
"A human group (band or tribe) visited the Chauvet cave during the first period around 36,000 years ago for cultural purposes," they wrote in an email to the Los Angeles Times. "They produced black drawings of huge mammals. Then, several thousands of years after, another group from another place with another culture visited the cave."
The two groups, separated by millenniums, had no connection with each other, they said.
The first round of human occupation was likely longer than the second. It is also when most of the drawings were done. Twenty-three charcoal drawings were sampled from different parts of the cave including the panel of the horses, the alcove of the lions, the panel of the reindeer and the panel of the bison.
Almost all of the radiocarbon dates of these drawings correspond to the oldest occupation phase, the authors found. Only two of them corresponded with the second occupation phase. This latter group of cave users were responsible for many of the torch marks on the wall.
Bears, which also left their mark on the cave walls through scratches over and under the art, appear to have used the cave from 48,500 to 33,300 years ago.
Although their occupation of the cave overlapped with humans, Quiles and Geneste said it is unlikely that both groups were there at the same time. They believe the bears used the cave to hibernate but spent spring and summer out of the cave. Perhaps it was only after the bears left that humans decided to use it.
"Humans would have to have avoided encountering the bears, as you can image," Quiles and Geneste said. "After all, a cave bear is an 880-pound carnivore!"
The authors were also able to determine that the end of each human occupancy of the caves coincided with rockfalls that may have sealed off the entrance to the cave, hiding it from humans for thousands of years.
The authors said the chronology of who used the cave and when will continue to become more precise as more data points are added to their model. But still, many questions remain. For example: Are the red paintings as old as the black paintings?
"Only the black paintings have been dated," Quiles and Geneste wrote. "The dating technique for the red paintings has yet to be developed."