How cave paintings are dated

Much like forensic crime investigators on any number of cop shows, archaeologists just need a speck of calcite - also known as "cave popcorn" - to begin unravelling the mysteries of a cave painting.

Calcite layers often form in limestone caves as rainwater seeps through rock, dissolving small amounts of calcium, which sometimes precipitates on top of cave paintings.

If archaeologists are lucky enough to chance upon these paintings, they can determine the age of the artwork through a process known as uranium dating, said professor of archaeological science Maxime Aubert from the Griffith University in Australia.

The technology allows researchers to date paintings that are up to 600,000 years old.

Professor Aubert told The Straits Times: "When the cave water precipitates on the painting, it also contains a small amount of uranium as well, since uranium is soluble in water.

"Over time, it starts to decay into an element known as thorium."

Thorium is not soluble in water, so the element would not have been present at the point of crystal formation, he added.

Since the decay rate of uranium into thorium is "precisely known", archaeologists can take a sample of the cave popcorn and measure the ratios of thorium and uranium found in it.

This information allows them to calculate when the calcite layer initially formed on the painting, which will thus give it a minimum age.

"So when we say that the calcite formed on the painting is at least 45,500 years old, it (the painting)could essentially be much older, possibly 50,000 or 60,000 years old," Prof Aubert said. "We don't know for sure."

But knowing the approximate age of a particular painting is sufficient in offering archaeologists glimpses into the artists who created them.

"It tells us that the people who created this artwork in Borneo and in Sulawesi were fully human - they're just like us," he said.

The Indonesian islands of Borneo and Sulawesi are thought to be crucial in the human migration route from Africa to Australia, where people had settled around 65,000 years ago.

"So if art had evolved from something simple to something more complex, it must have happened a long time ago, probably back in Africa," Prof Aubert said.

"The humans who migrated from Africa were fully modern, and they had the capacity to make any art they wanted."

Many secrets from the far distant past have been unlocked by other cave paintings found around the world. Here is a look at some of them:

1. WILD CATTLE AND HAND STENCILS IN BORNEO

PHOTO: PINDI SETIAWAN

A painting of three animals that seem to resemble wild cattle known as banteng was found in a limestone cave on the Indonesian island of Borneo.

Researchers have determined the artwork, which is made from an iron-oxide pigment known as ochre that gives it its orange-red hue, to be at least 40,000 years old.

The findings were published in the Nature scientific journal in November 2018.

Several hand stencils that were painted in the same shades were alongside the cattle.

Two were found to be at least 37,000 years old, while the third had a maximum age of around 51,800 years.

And a second set of paintings, depicted with dark purple hand stencils, were found to be around 20,000 years old.

Researchers used these discoveries to deduce that the cave paintings had likely appeared in Borneo between 40,000 and 52,000 years ago. The paintings also offer insights into how rock art traditions emerged and were passed down among generations within South-east Asia.

2. HUNTING SCENE IN SULAWESI

The Sulawesi rock art panel depicts a hunting scene where mythological part-human and part-animal hunters are in search of wild pigs and a small buffalo. PHOTOS: RATNO SARDI

A rock art panel depicting a hunting scene was found in a limestone cave in Sulawesi, Indonesia.

The hunters, who are painted in reddish-brown colours, are believed to be part-human and part-animal and in search of wild pigs and a small buffalo.

Known in mythology as therianthropes, the hunters are said to be people who have the ability to shape-shift into other animals.

Researchers from Australia's Griffith University have determined that the painting is at least 43,900 years old, according to findings in the Nature journal in 2019.

They noted that the scene is one of the oldest records of storytelling, adding that it is very rare for such a highly advanced artistic piece to be created at that time.

Scenes in cave art had begun appearing some 21,000 to 14,000 years ago, making such clear depictions of the therianthropes all the more uncommon, they said.

3. HAND STENCILS AND DEER-PIG IN SULAWESI 

PHOTO: KINEZ RIZA

Researchers found a 35,400-year-old cave painting of a deer-pig, or a babirusa, and a human hand print that is at least 39,900 years old at the Maros cave sites in Sulawesi.

The discovery was among 12 human hand stencils and two animal depictions from a total of seven cave sites, noted researchers in the Nature journal in 2014.

4. LASCAUX CAVE PAINTINGS IN SOUTH-WESTERN FRANCE

PHOTO: AGENCE FRANCE-PRESSE

The famous Lascaux caves in the Montignac village in south-west France has over 600 paintings covering the interior walls and ceilings of the cave.

Discovered in the 1940s, the paintings are mainly of animals, such as horses, deer and aurochs - an extinct type of cattle - and are estimated to be between 15,000 and 17,000 years old.

One of the most famous chambers in the caves is the Hall of the Bulls, which mainly features the aurochs.

The original cave was closed in 1963, after carbon dioxide and heat from visitors, among other contaminants, caused damage to the paintings.

A replica of the Hall of the Bulls section was opened for public viewing in 1983 near the original cave.