When did humans first arrive in Southeast Asia?

In 2009, when our team first found a human skull and jawbone in the Tam Pà Ling cave in northern Laos, some were skeptical about its origin and actual age.

When we posted a timeline in 2012 for the arrival of modern humans in mainland Asia around 46,000 years ago, according to evidence from Tam Pà Ling, skeptics remained.

In short, the site got a bad rap. One of the most interesting caves in mainland Southeast Asia was frequently overlooked as a possible route in the accepted path of human dispersal in the region.

However, in new research published in nature communications, we report more human remains found at Tam Pà Ling, and a more detailed and robust chronology for the site. This shows that humans arrived in the region at least 68,000 years ago, and possibly 86,000 years ago.

Lots of evidence, but hard to date

Our team of Laotian, French, American and Australian researchers have been excavating at Tam Pà Ling for many years. As we dig, we find more and more evidence of A wise man in ever earlier times.

First there was a finger bone, then about 2.5 meters deeper, a chin bone, then part of a rib. In all, eight pieces were found in just 4.5 meters of sediment, which may not sound like much, but it’s huge in archaeological terms.

Surely, we thought, this would be enough for Tam Pà Ling to take its place among the first sites of human arrival in Southeast Asia.

But one obstacle remained: the cave is difficult to date. This has prevented its importance from being recognized, and without a convincing chronology, the evidence from the cave will not be included in the debate about early human movements.

Many common dating methods cannot be used

There are some difficulties in dating Tam Pà Ling.

First, human fossils cannot be directly dated as the site is a world heritage area and fossils are protected under Laotian law.

Second, there are very few animal bones and no proper rock decorations, either of which could be used for dating.

And third, the entrance to the site is wide and steep. This means that any charcoal found in the cave, which is useful for dating, may well have come from outside, thus bearing little relationship to the age of the sediment inside.

This means that the backbone of the timeline must be established by dating the sediment itself, using techniques such as luminescence dating.

Signs in buried minerals

Luminescence dating relies on a light-sensitive signal that accumulates in buried sediments and resets to zero when exposed to light.

This technique mainly uses two minerals: quartz and feldspar.

Quartz can only be used at the youngest levels, as it is limited by the amount of signal it can hold. In the deeper layers, age can often be underestimated, so at Tam Pà Ling we only used quartz to date the top three meters of the sediment.

For the lower levels (four to seven meters), we had to switch to feldspar dating to fill the gap in the age profile. Below twenty feet, the feldspar grains began to wear away and we had to resort to fine-grain dating, using tiny mineral grains mixed together.

dating teeth

Tam Pà Ling is relatively poor in animal evidence. However, two teeth from a cow-like animal were eventually unearthed from 6.5 meters below the ground which could be dated using two distinct techniques.

Uranium serial dating works by measuring the uranium and the elements it is transformed into through radioactive decay, inside the tooth. Electron spin resonance dating is based on measuring the amount of electrons in tooth enamel.

Each technique provides an individual numerical age for the fossil. By combining the two, we obtained robust direct dates, which can complement the luminescence chronology.

A closer look at the sediments

To make the dating as strong as possible, we used whatever techniques we could, such as applying uranium serial dating to a stalactite tip that had been buried in sediment.

We also began to back up all of our dating evidence with very detailed analysis of the sediments to assess the origin of the fossils.

Micromorphology is a technique that examines sediments under a microscope to establish the integrity of the layers that buried the fossils.

This is a key component of the new chronology, as it helped establish that there was a fairly constant accumulation of sediment layers over a long period.

By 2022, we had amassed a series of dating evidence that could be modeled to determine the exact age of each layer and the fossils they buried.

A stop on the route of human dispersal

Our updated chronology revealed that humans were present in the vicinity of Tam Pà Ling Cave for approximately 56,000 years. It also confirmed that, far from reflecting a rapid dumping of sediment, the site contains sediment that accumulated steadily for some 86,000 years.

The age of the lowest fossil, a fragment of a leg bone found seven meters below the surface, suggests that modern humans arrived in this region between 86,000 and 68,000 years ago.

Evidence from Tam Pà Ling has delayed the timing of A wise man arrival in Southeast Asia. This suggests that the mainland, along with coastal and island locations, may also have been a viable dispersal route.

Tam Pà Ling is a stone’s throw from Cobra Cave, where i found a tooth about 150,000 years old belonging to a Denisovan, the now extinct human relatives known only from remains found in Siberia and Tibet. This suggests that the site may be on a dispersal route previously used among hominins.

Tam Pà Ling continues to reveal pieces of the puzzle of the ancient human journey through the world. Only time will tell how many more he has in store.

Kira Westaway is Associate Professor in the School of Natural Sciences at Macquarie University. Meghan McAllister-Hayward is a PhD candidate. Mike W. Morley is an Associate Professor at Flinders University. Renaud Joannes-Boyau is Associate Professor at Southern Cross University. Vito C. Hernández is a doctoral candidate. This article is republished from The conversation.