How old are the oldest millennia

Cultural heritage in dangerClimate change is destroying cave paintings that are thousands of years old

The oldest discovered cave paintings of Homo sapiens have been preserved on the Indonesian island of Sulawesi. The early works of art include simple hand outlines, but also detailed drawings of Sulawesian deer boars as well as hunting scenes in which strange hybrids of animals and humans chase a fleeing wild cattle.

Jillian Huntley of Griffith University in the Australian state of Queensland recently took a closer look at some of the cave paintings: "The place we worked on is called Maros-Pangkep. This is an area an hour and a half drive from the town of Makassar in South Sulawesi. There are limestone caves there, in which wonderful rock carvings have been preserved. "

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But the ravages of time are gnawing at the works of art, and the weathering is affecting them, says Jillian Huntley: "The paintings themselves are very detailed with all their very fine lines. Unfortunately, the surface of the limestone on which they were painted is loosening, from the wall."

Salt crystals grow under the rock paintings

In almost all of the 300 or so sites that have so far been examined for absolute age dating, the scientists found flakes with flaked paintings on the cave floor. And it looks like the rock art has been peeling faster and faster since its discovery in the 1950s.

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"We wanted to find out why. So I first examined the cave walls with a portable X-ray fluorescence spectrometer. It showed that salts were crystallizing on these walls. Then we took some of the fallen rock flakes into the laboratory. We examined them with the scanning electron microscope and with high intensity X-ray light. That way we were able to identify exactly why these flakes fell off: it is precisely because of these salts. "

This is because the sulfur content in limestone can be increased, as can the content of calcium sulfate and sodium chloride salts. Then, when water seeps through the porous rock, these chemicals dissolve. If the water evaporates again, the dissolved salts precipitate.

Destructive interplay of the elements

The salt crystals both grow up and under the paintings - and the latter is the most damaging, says Jillian Huntley: "They form under the painted surface layer of the limestone, creating a mechanical pressure that pushes these little flakes off the wall and actually does destroyed the works of art. "

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This process seems to be faster today than it was half a century ago. The researchers see climate change at work: "The daytime temperatures are higher than before and the dry periods longer. This means that more salt particles crystallize out of the solution. At the same time, the monsoon rains have become more intense, so that more moisture penetrates the subsoil, which causes the salt crystals to swell more. So they are not stable, but grow and shrink depending on how hot it is and how much moisture there is in the air. And this increased shrinking and swelling of the crystals causes the rock to flake off more intensely. "

There is no remedy, says Jillian Huntley. The only thing that remains is to document the works of art as precisely as possible and thus preserve them for posterity.