What archaeologists find in this cave — deep in the heart of Borneo’s rainforest — could shed light on one of the biggest mysteries in human history.
The gaping mouth of Trader’s Cave emerges from under the canopy of jungle and trailing vines.
Swiftlets flit in and out of its cavernous guts.
During nesting season from August to March, local Penan men shimmy 15 metres up bamboo poles barefoot to collect the birds’ nests, which are sold for soup and traditional Chinese medicine.
Wooden platforms, where the men used to live up until the 1970s, sit just inside the cave’s entrance.
But bird nest traders were not the first humans to live in this cave.
Clues about who called this place home thousands of years ago are hidden in layers of sediment that have been deposited on the cave floor.
And that is what Darren Curnoe has come to find.
Professor Curnoe, who is co-leading the excavation with members of the Sarawak Museum, hopes this dig can shed light on when humans like us — Homo sapiens — first arrived in South-East Asia.
“We have no sense when the very earliest modern humans really arrived in [South-East Asia],” says Professor Curnoe, of the ARC Centre of Excellence for Australian Biodiversity and Heritage.
“These are the ancestors of the Indigenous people across South-East Asia and Australia and New Guinea.”
An iconic fossil site
Trader’s Cave is set in limestone mountains that stick out of the rainforest in the Niah National Park, close to the northern coast of Borneo in Malaysia.
It is part of the Niah Great Cave complex, some of the largest caves in South-East Asia.
The most famous is the West Mouth of Niah Cave, 200m away from Trader’s Cave.
“It is so big you can fit four jumbo jets inside. It’s enormous,” Professor Curnoe says.
The caves are also one of the most important fossil sites in the region.
Over the past 60 years, archaeologists have uncovered the remains of hundreds of skeletons in a Neolithic cemetery up to 4,000 years old, and an Iron Age cemetery up to 2,000 years old.
It is also where an iconic fossil known as Deep Skull was unearthed in 1958 by British palaeontologists Tom and Barbara Harrisson.
Deep Skull belonged to a middle-aged woman who lived around 35,000 years ago.
“Until recently, Deep Skull provided the earliest physical evidence [of humans in South-East Asia] that we had,” Professor Curnoe says.
“As of last year, there’s a study from Indonesia that suggests modern humans first arrived in South-East Asia between about 60,000 and 70,000 years ago.”
If it’s right, that timing would place modern humans in the region soon after one of the most catastrophic events in Earth’s history.
“Just before the time that modern humans get into South-East Asia, we have the largest volcanic eruption that’s happened on the planet in the last two million years.”
The eruption that changed the world
A massive crater lake on the Indonesian island of Sumatra — around 1,700 kilometres west of Trader’s Cave — marks what is left of the Mt Toba super-volcano.
Around 74,000 years ago, the cataclysmic explosion showered the region in ash and plunged the planet into a volcanic winter, which some scientists believe wiped out most humans on Earth.
Professor Curnoe and his team hope to find evidence in Trader’s Cave of what happened at that time.
Were the caves occupied before or during the eruption? And, if so, who were the people living there?
“If there were people living in the area at the time, including at Niah Caves, that they would have been dramatically affected by this super-eruption,” he says.
“It’s been thought for a long time that this super-eruption laid the foundation for modern humans to come in after that event.
“It kind of put the broom through the neighbourhood, and got rid of … ancient humans living there.”
And just as we don’t know when these ancestors arrived, we also don’t know how they survived in the rainforest.
“Rainforests are surprisingly challenging places for hunter gatherers to live,” Professor Curnoe explains.
“You’ve got plants and animals living high up in the rainforest canopy, and a lot of the plants that are on the ground are often toxic.
“So it’s been thought for a long time that rainforests are environments that were only ever occupied by modern humans — people like us.”
Until recently, Trader’s Cave was not thought to contain anything significant, and was overlooked as a fossil site.
“Our excavations mark a new phase in the history of Niah, and are the first Palaeolithic digs in the cave in 50 years,” Professor Curnoe says.
The archaeologists start their trek to the caves just after sunrise each day.
“It’s an incredible part of the day with insects, birds, a number of primates; monkeys and gibbons, all making their early morning wake-up calls,” Professor Curnoe says.
The team includes local bird nest collectors, who work on the dig in the off season.
After leaving their base camp, they make the short trip across the Niah River by boat.
“You occasionally have the privilege of seeing a 2 or 3m crocodile,” Professor Curnoe says.
The team then walks for 40 minutes along a boardwalk path through the jungle to the cave.
“You enter a quite a different world,” Professor Curnoe says.
“It’s not dark, it’s that kind of in-between state of a bit of bright light and dark pockets in the cave.
“If a storm blows over — it’s the tropics and storms happen often — the cave is plunged into darkness.
“The sounds are mostly of birds, and there’s the odd bat that flies in and out of the cave.”
The caves are also filled with the sound of tourists.
The Niah Cave system is one of Borneo’s prime travel destinations.
“Some days there are three or four hundred people coming through,” Professor Curnoe says.
Each day the team set up generators and lights and get to work as the tourists pass by.
“Everybody’s surprised to see a group of archaeologists,” Professor Curnoe says.
“They want to stop and have a chat and find out what you’re doing, what you’re learning about the past and their heritage.”
Archaeology is a very physical discipline.
“If you’re not excavating, you’re sitting or you’re surveying, climbing about in caves,” Professor Curnoe says.
“The deeper we get, the more humid it gets and hotter it gets too, so we are digging under hot conditions. You’re constantly sweating.”
The team chip painstakingly away in a 3-by-3-metre square.
“We dig by hand using archaeological trowels so it’s very labour intensive,” Professor Curnoe says.
As they scrape and brush away sediment they mark their finds with flags.
White is a shell, yellow is bone, green is a stone artefact, red is an area that has been burnt.
Buckets of sediment are taken outside where they are washed and sieved for fine fragments.
Each item is logged, measured and bagged, to be analysed later under a microscope and dated.
“We study it very carefully trying to identify what it is,” Professor Curnoe says.
“Is it human or is it something else? If it’s something else what species is it? Is it a deer or a crocodile? Or a turtle? What part of the body does it represent?”
The stone tools are analysed as well.
“We have to identify the raw material they are made from, understand how the tools were made, and try and get some insights into how these tools were used,” he says.
Digging back in time
They dig down half a metre across the 3-by-3-metre square.
They move slowly down through the sediments, 5 centimetres at a time.
Each layer takes them further and further back in time.
In one corner they’ve excavated a pit that reaches down 2m.
As they get deeper, the earth changes colour — yellow clay shifts into a layer of shell and bone, more clay, then layers of red and grey.
As they dig down, Dr Xeufeng Sun from Nanjing University bangs metal tubes into the wall, and stuffs them with black plastic bags.
He takes samples to accurately date the layers using a technique that detects when grains of sand last saw sunlight.
“We’re now starting to get quite a good sense of how old these deposits are,” Professor Curnoe says.
“The very top of our site begins at about 35,000 years ago.
“That very ancient cave floor that we are focused on … we know is some around 50,000 or 55,000 years old.
“Immediately beneath it are deposits that date between about 60,000 back to about 80,000 years.
“I think the potential is there to push it back to about 100,000 years.
“We are talking about quite a long window, but crucially that window covers the period when modern humans settled the area, and also the time of the Toba super-eruption.”
A rich record of cave life
Trader’s Cave rewards their hard work.
By the end of three weeks the team has unearthed charcoal hearths, shells, animal bones, and human bones.
“Trader’s Cave has turned out to be a remarkable site in providing, really quite a rich record of early humans in the region,” Professor Curnoe says.
“We have turtle bones, crocodile bones, and deer bones that have cut marks on them, … evidence that humans were exploiting, were feeding off these remains, these creatures.
“But for me the thrill is finding the hard physical evidence for people. And we have that.
“We found only fragments of human skull bone, but we hope in the future we … might find a jaw or even a complete skull to give us a much clearer picture of who these people were.”
The rich layers containing evidence of life are around the 50,000 to 55,000 year mark, which suggests humans were in these caves at least 20,000 years earlier than Deep Skull if the dates are confirmed.
But there is no evidence of human fossils in deeper layers corresponding to the Toba eruption in the 2-metre square.
Professor Curnoe is optimistic evidence of older humans that lived before or during the cataclysmic event may still lie in the deeper layers of other parts of the cave.
Over the next year, he plans to return to the cave in search of human remains and stone tools at the very bottom, and refine the dating. He hopes to build a much more detailed picture of life in the Borneo rainforest thousands of years ago before the Toba eruption.
“Each time we go back the dig gets bigger … but of course we really need to focus on these very early layers in the cave,” Professor Curnoe says.
“What we really hope for is that we can find some human remains at the very bottom … who were perhaps older than 80,000 years ago, and identify who they were.
“Were they modern humans like us? Did we settle that part of the world this early, or were these the last of the archaic people living in the area before our kind got in?”
Words and production: Genelle Weule
Photographs and video: Darren Curnoe
Editor: Tim Leslie