Dec 6, 2023

By Dyani Lewis 6 December 2023 Ancient humans painted scenes in Indonesian caves more than 45,000 years ago, but their art is disappearing rapidly. Researchers are trying to discover what’s causing the damage and how to stop it — before the murals are gone forever. On the southwestern peninsula of Sulawesi in Indonesia, a vast series of karst mountains rise like great knobby boulders from the flat floodplain. Beneath the lush tropical vegetation that blankets the spires, there are hundreds of caves, crevices and rock shelters — carved over millennia by water seeping through the porous limestone. For tens of thousands of years, these eroded cavities provided shelter for the region’s ancient residents, who left behind a pictorial record of their time there. On the walls, archaeologists have found painted hand stencils, stick-figure people and ochre-coloured depictions of warty pigs and miniature buffalo. The limestone hills of the Maros–Pangkep karst landscape hold hundreds of caves with ancient art. An ancient painting of an anoa — a dwarf buffalo — in Leang Pettae, a cave in the Leang Leang Archaeological Park. Rustan Lebe, an archaeologist at the Cultural Preservation Office, an Indonesian government agency in Makassar, has been systematically documenting the caves scattered across the regencies of Maros and Pangkep — and the artwork inside them — since 2016. Some sites are deep in the tropical wilderness; others sit behind houses and are used by villagers as grain stores and temples; many are located on land where companies are mining marble and limestone for cement. Lebe’s database currently records 654 caves, and he estimates that he and his team have so far explored less than half of the karst hills. According to Lebe, a staggering 65% of sites contain cave images, some of which were drawn more than 45,000 years ago1 — making them some of the oldest pictures in the world . But as fast as Lebe is finding the cave paintings, he is seeing others vanish before his eyes. The Maros–Pangkep karst landscape is the second-largest such terrain in the world. A view into the lower chamber of the Bulu’ Sipong 4 cave, located in the Semen Tonasa mining concession. An archaeologist from the Indonesian Cultural Preservation Office stands inside the lower chamber of Bulu’ Sipong 4. "Our big problem now is the peeling of the surface of the rock," he says. Panels of images that have survived since the middle of the last ice age are flaking off the cave walls at an alarming rate. The hard, crusted surface of the cave walls, on which the ancient people painted, is breaking off from the powdery white limestone underneath in a process called exfoliation. Archaeologists working in the caves have speculated on the causes. Perhaps it's the pollution from nearby cars and trucks, the heavy-breathing visitors who change the caves' microclimate or the changing weather patterns ushered in by climate change. But researchers also wonder whether local industry is at fault, particularly the dust and vibrations produced by mining companies that blast open the karst cliffs, digging for limestone. The image of a babirusa, or deer-pig, in Bulu’ Sipong 4 is flaking away, revealing the white limestone underneath. The company Semen Tonasa blasts apart the karst landscape for limestone that it uses to make cement. Researchers are now racing to decipher which factors are causing the rock art to flake away. In September, I joined Lebe on a trip while he investigated the deterioration. This quest to understand the risks to the cave has forged unlikely alliances between government archaeologists, local and international scientists, mining-company executives and investors from as far away as Norway. All are seeking to halt the damage to the artwork before the paintings are lost for good. With several factors probably implicated in the rock art’s demise, scientists are only beginning to understand the complex processes at play. Work so far is “the tip of probably quite a terrifying iceberg”, says Jillian Huntley, an archaeologist at Griffith University’s Gold Coast campus in Southport, Australia. “There’s an urgency to funding more research in this space,” she says. Earliest art The incredible antiquity of the Maros–Pangkep artwork was discovered almost by chance. In 2011, archaeologist Adam Brumm, then at the University of Wollongong in Australia, went to Sulawesi to dig for bones of ancient people who had migrated to the region’s islands during the last ice age, when sea levels were lower than they are now. During breaks from excavating, Brumm visited nearby caves adorned with images that were assumed to have been made by Neolithic farmers less than 10,000 years ago, although no researchers had attempted to date them. Scratch marks on a piece of ochre rock were produced by an ancient painter making powdered pigments. Scratch marks on a piece of ochre rock were produced by an ancient painter making powdered pigments. In Leang Jarie — the Cave of Fingers — Brumm noticed “funny little growths” on top of the coloured hand stencils, and he mentioned them to Maxime Aubert, his office mate back in Wollongong. Aubert, a geochemist and specialist at dating rock deposits, realized that these nodules, called coralloid speleothems, could be the key to discovering when the underlying images were made. The next field season, Aubert paid his way to Sulawesi to collect the knobbly stalactites for dating. Back in Wollongong, he estimated that the hand stencils were made 40,000 years ago2. This made them the oldest known hand stencils at the time. And images of pigs in the cave were potentially some of the oldest — if not the oldest — examples of figurative art depicting recognizable objects. “I saw the age, and I said ‘oh shit’!” says Aubert, who is now at Griffith University in Southport. “We knew straight away it was really, really important,” he says, because it challenged the Eurocentric view of the origins of cave art2. The people who painted the Maros–Pangkep murals did so on a hardened outer crust that forms when water leaches through the cave wall, bringing with it calcium carbonate and other minerals. That process continued after the images were drawn, sealing the pigment into a hardened skin that bears little resemblance to the chalky rock underneath. “Rock art is all about crust,” says Benjamin Smith, an archaeologist and rock-art specialist at the University of Western Australia in Perth. “If you lose the crust, you lose the rock art,” says Smith. And that’s precisely what Lebe and others are seeing: paintings are lost as patches of crust flake off. Archaeologist Rustan Lebe shows how ancient humans made hand stencils in the lower chamber of Bulu’ Sipong 4. Lebe points to an ancient hand stencil amid spall scars — white patches where the surface of the rock has flaked away. Sacred spaces An hour and a half’s drive north of Makassar is the headquarters of the Semen Tonasa cement company, a subsidiary of the majority state-owned SIG, Indonesia’s largest cement-producing firm. The karst mountains of Maros–Pangkep are treasured by cement companies, which reduce entire mountains of limestone to rubble and haul the rocks away to make cement. When cave art near the firm’s operations was found to be more than 43,000 years old3 in 2019, Semen Tonasa became the unlikely custodian of one of humanity’s most prized cultural treasures. Bulu’ Sipong is a dome-shaped mound less than a kilometre from Semen Tonasa’s head office. Donning a hard hat and steel-capped boots, I joined Lebe and a procession of company employees to visit Bulu’ Sipong 4, one of the mound’s eight caves. A steep steel staircase delivered us to a cave entrance. Inside, Lebe pointed out faint hand stencils that I would probably have missed otherwise. On a low, sloped ceiling in the cave, someone had placed their hand — the same size and shape as my own — on the rock and blown ochre on it to create a stencil. The faded spray of ochre remains, tens of thousands of years later. Next, I followed Lebe up an 8-metre ladder to Leang Bulu’ Sipong 4’s upper chamber. Once I had joined him, we stood near a tall opening — a natural balcony — to cool off and lower our breathing rate before getting too close to the artwork inside. The cave had probably been no easier to reach for those who painted its walls, Lebe told me. They didn’t come there to gather around a fire or shelter from the weather, he explained. Instead, they went there for the purpose of painting. It was a place for the sacred, not the domestic, he says. Lebe ascends a ladder into the upper chamber of Bulu’ Sipong 4. Before entering the cave, Lebe stops to catch his breath and cool down, to limit how much he alters the climate inside the shelter. Entering the cathedral-like chamber, light from outside the cave was almost enough to illuminate a stunning 4.5-metre-long wall panel of images3. One end of the panel depicts a hunting scene, with six stick figures and lines that could be spears or ropes extending towards an anoa (Bubalus sp. ), a dwarf buffalo local to Sulawesi. On closer inspection, the figures reveal themselves to be human–animal hybrids, or therianthropes — human bodies with beaked bird heads or long tails. The world’s oldest hunting scene shows tiny hunters (left) with lines extending towards a dwarf buffalo. The hunters are human–animal hybrids — therianthropes — such as the beaked figures in the top left. The hunting scene is less an account of past events, and more a retelling of an ancient peoples’ folk tale or myth. But the full story can’t be known. Images are obscured by white holes, called spall scars, in the crusted canvas. Closer to the cave entrance, the crust — and any paintings it might have held — is completely gone. There, the walls are chalky white and unremarkable. According to dating work by Aubert, the Bulu’ Sipong 4 panel was painted at least 43,900 years ago, making it the oldest story-telling artwork in the world3. “It’s the first evidence for humans to imagine the existence of something that doesn’t exist,” says Brumm, who is now at Griffith University’s Nathan campus in Brisbane. It’s more than twice the age of the famous 17,000-year-old ‘Shaft scene’ in the Lascaux cave in France. In that painting, a man with a bird-like head is being charged by a wounded bison. The painting in Bulu’ Sipong 4 is also older than the German ‘Lion-man’ — a 40,000-year-old ivory figurine of a lion-headed person. Flaking away Brumm, Aubert and their colleagues published their findings3 about the Bulu’ Sipong 4 hunting scene in December 2019, and that attracted media attention to scientists’ concerns about the potential for exfoliation to destroy the artwork. Some reports pointed to Semen Tonasa as a seemingly obvious culprit of this deterioration, because of the location of the cave. But there are signs that the Maros–Pangkep cave art has been flaking away for hundreds or even thousands of years. In one cave, Dutch graffiti has been scrawled across a painting and a spall scar left by flaking carries the inscription “AD 1769”. In others, there are charcoal images etched by Austronesians a few thousand years ago that cover older hand stencils as well as spall scars. Nevertheless, local people — some of whom act as custodians of individual caves — say that the exfoliation rate has sped up over recent decades. And Lebe has documented deterioration in action. Photos that he has taken — just months apart — reveal growing spall scars that are chipping away at the invaluable cultural heritage at an alarming rate, a sign that deterioration might have accelerated. Bulu’ Sipong 4 is located just 2 kilometres from Semen Tonasa’s cement factory and less than 3 kilometres from the open-cut blast site where limestone is gathered for processing. When the paintings were discovered, a daily procession of trucks — kicking up dust as they went past — rumbled down an unsealed dirt road just 100 metres from the cave. Semen Tonasa’s cement factory is less than 3 kilometres from the Bulu’ Sipong 4 cave, on the right side of the hill in the foreground. (This video has no sound) Semen Tonasa’s cement factory is less than 3 kilometres from the Bulu’ Sipong 4 cave, on the right side of the hill in the foreground. (This video has no sound) In February 2020, The Guardian newspaper published an article about the threat of Semen Tonasa’s mining activities to the “world’s oldest art” . The article landed in the inbox of Hilde Jervan, chief adviser at the Council on Ethics for the Norwegian Government Pension Fund Global (GPFG). The fund was set up in 1990 to invest earnings from the country’s North Sea oil field. Its global assets are worth US$1.5 trillion, and the council is tasked with ensuring that the fund’s money is spent ethically. The GPFG owns less than 2% of the SIG, but the stake was sufficient for Jervan to contact Semen Tonasa to find out what the company was doing about the possible threat that its operations were posing to local cultural-heritage sites, including Bulu’ Sipong 4. The fund “has some leverage in the market because it’s so big”, says Jervan, and when the Council on Ethics publishes its assessments, other investors take notice. Jervan’s team hired independent archaeologists Matthew Whincop and Noel Hidalgo Tan, who visited Bulu’ Sipong 4 in 2022 to assess whether Semen Tonasa’s activities might be damaging the nearby cave art. There was an assumption that the exfoliation seems to be intensifying, says Whincop, and “therefore the closest development must have something to do with it”. But Whincop, who is based in Brisbane, Australia, says that their main challenge was “a serious lack of data”. Information was sparse for the exfoliation rates, dust levels, humidity, and pollution and vibrations from the blasts and mining trucks, and the data spanned such a short period that it was impossible to discern what factors might be causing the images to flake off. Dust rises as Semen Tonasa workers use explosions to mine the limestone. (This video has no sound) Dust rises as Semen Tonasa workers use explosions to mine the limestone. (This video has no sound) The lack of data is not unusual, says Paul Taçon, a rock-art scientist at Griffith University in Southport. “There’s not enough monitoring [being] done,” he says, even though it’s extremely important for detecting and preventing damage. Halmar Halide, a hydrometeorologist at Hasanuddin University in Makassar, has been working with Lebe to monitor conditions at several caves every three months. They measure airborne particulates, such as dust and pollution, as well as temperature, humidity and the extent of exfoliation. They are also collaborating with Semen Tonasa to work out what equipment should be purchased for a more comprehensive monitoring programme. Scientists Halmar Halide (left) and Andika measure the weather conditions at the Leang Pettae cave. Scientists Halmar Halide (left) and Andika measure the weather conditions at the Leang Pettae cave. “We are a cement company, so we are really not specialized in cultural-heritage management,” says Johanna Daunan, head of sustainability at SIG in Jakarta. But she says that the company is committed to doing what it can to protect the sites and it has already taken measures to reduce the amount of dust coming from its operations. One problem, says Daunan, is that there are few government regulations to guide the firm on what levels of dust, pollution and vibrations might be safe for the rock art. Fragile paintings Lebe and others who work in the caves are convinced that dust from Semen Tonasa’s mines — and others in the region — is a big problem. “Absolutely the dust comes into the caves,” Lebe says, “especially the caves situated near the mining and industries.” Although he is concerned about the impacts of Semen Tonasa’s activities, they are only one of several mining operations in the region that he says could be affecting the cave art. A spokesperson for one company, Bosowa Semen in Maros, told Nature that it is not aware of heritage sites located in its mining concession and that it will let Lebe know if its employees find any caves; Lebe has not been granted permission to explore that area. Even so, diagnosing the sources of deterioration for rock art is a challenge all around the world. Every site is unique, and causes can range from biological and physical to behavioural ones. In India, visitors scrawl over the top of prehistoric paintings, or chisel them off as souvenirs. In Tanzania, tour guides throw water onto images to brighten the contrast, not realizing that it causes the pigments to fade and disappear. Even the mere presence of people can alter a cave’s microclimate, bumping up the temperature, humidity and carbon dioxide levels with each exhaled breath. In the Lascaux cave, this caused the growth of algae, fungi, bacteria and salt crystals, so access is now limited. Pollution from traffic and agriculture can also cause untold damage. Dry pollution particles can, when combined with water or moisture in the air, turn to nitric or sulfuric acid, which dissolves the rock face and any artwork on it, says Johannes Loubser, a rock-art specialist based in New York City. Researchers have set up a rudimentary experiment to collect and measure dust levels in Bulu’ Sipong 4. They intend to replace the equipment with more sophisticated technology. Researchers have set up a rudimentary experiment to collect and measure dust levels in Bulu’ Sipong 4. They intend to replace the equipment with more sophisticated technology. Huntley has been investigating another factor that contributes to the flaking cave walls: climate change. While examining flake samples under a scanning electron microscope, she found tiny pillars of salt that had formed behind the hardened crust4. Those salt crystals grow and shrink with changes in humidity, says Huntley. When wet, “they expand up to three times their size”, she says, which mechanically forces the rock crust off the wall. Climate change and changing land use are speeding up this process, says Huntley. Higher temperatures across the tropics are causing more frequent and severe droughts. At the same time, rains dumped during the monsoon season are retained in the now-abundant rice fields and aquaculture ponds. Together, this provides ideal conditions for the formation of salts and the cycles of swelling and shrinking that weaken the crust. Huntley says that climate change could be affecting cave art elsewhere, too. But international bodies such as the International Council on Monuments and Sites — which advises the World Heritage Committee of the United Nations cultural organization UNESCO — are only just starting to consider the indirect impact of climate change on cultural-heritage sites, she says. Humidity and airborne dust could also work together to make the situation worse, says Whincop. Humidity can cause dust particles to stick to the cave wall, he says, obscuring the images, and the added weight makes the crust more susceptible to flaking. Inside Bulu’ Sipong 4, there is “dust over everything”, he says, and that is probably contributing to the exfoliation, “but we just do not have the data” to say for sure. It was this frustrating lack of data that led Whincop to conclude, in his report to the Council on Ethics, that there was no clear evidence that Semen Tonasa’s activities were harming the Maros–Pangkep rock art. “We can’t definitively say it’s all climate change, or it’s all Semen Tonasa,” says Whincop, because there’s no hard evidence linking any one factor — or combination of factors — to the accelerated flaking. The world’s oldest hunting scene is located in a cave close to Semen Tonasa’s cement factory. The world’s oldest hunting scene is located in a cave close to Semen Tonasa’s cement factory. Saving the cave art But the report also concluded that the company needed to do more to prevent damage, in particular from dust, blast vibrations and humidity caused by water-filled clay pits. And in May, Norges Bank — which manages Norway’s GPFG — placed Semen Tonasa under observation for three years, to track their progress and make sure that heritage-management plans are implemented. In October, Whincop returned to see how much progress the company had made. “They are making progress, though a bit slowly,” he says. The company has hired John Peterson, an independent archaeologist based in Cebu City in the Philippines, to draft a comprehensive heritage-management plan, which Daunan says is in the final stages of review before it is made publicly available. Whincop says that the plan includes monitoring protocols that will help to determine what is affecting the rock art. “They will likely need a year or two of data collection before being able to make any meaningful conclusions,” he says, so further interventions will probably happen only after that. But he’s reassured that Semen Tonasa is committed to doing what it can to prevent damage to the rock art. Since he visited in 2022, the company has sealed the road’s surface that runs alongside the Bulu’ Sipong mound and increased the number of water trucks that wet the now-sealed road to reduce the amount of dust produced by heavy vehicles driving by. “Probably the most reassuring development is that [Semen Tonasa now] has a dedicated sustainability team working on this issue,” says Whincop. A truck sprays water onto the road near Bulu’ Sipong to minimize dust levels. Water-filled pits from abandoned clay mining surround the hill. A truck sprays water onto the road near Bulu’ Sipong to minimize dust levels. Water-filled pits from abandoned clay mining surround the hill. Lebe and his team at the cultural-heritage office lack the resources to fund sophisticated investigations into the plethora of variables that affect cave-art deterioration. In that respect, Peterson says, it might turn out to be fortunate that Bulu’ Sipong 4 lies in Semen Tonasa’s mining concession. The company has the means to fund a comprehensive monitoring programme that could end up providing crucial clues about what’s harming caves throughout the Maros–Pangkep karst landscape, says Peterson. Along with the shortage in resources, there is also limited awareness of the caves and their cultural heritage. “As an Indonesian, I only just found out that there are more than 500 caves in the Maros–Pangkep area, which is astonishing,” says Daunan. “Not that many Indonesians know about this,” she says. That could be changing slowly. In May, the karst landscape stretching across Maros–Pangkep was officially declared a UNESCO Global Geopark. This status could attract extra resources from the Indonesian government in the future. But Huntley says that more urgent investigations to stem the deterioration are needed. Meanwhile, Brumm is trying to create a digital record of the cave art, which could help with its conservation and enable people to experience the paintings without harming them. “What we do need to do right now,” he says, “is to create a 3D visual archive of all of the rock art there, before it’s gone.” Standing in the cave next to the peeling paintings, it’s hard to grasp their vast age. It’s equally hard to fathom how many more hand stencils, warty pigs and hunting scenes might be tucked away in as-yet-undiscovered caves in Maros–Pangkep — and that they might disappear soon, never revealing their magnificence to modern eyes. Author: Dyani Lewis Media editor: Agnese Abrusci