Archaeologists from Flinders University, along with an international team, have discovered evidence of the earliest Homo sapiens fossils on the Southeast Asian mainland by analyzing microscopic layers of soil at Tam Pà Ling (Monkey Cave) in north-eastern Laos.

For 14 years, a team of scientists from Laos, France, the United States and Australia has been studying this site, which has yielded the oldest fossil evidence of human ancestors. The latest study, published in Quaternary Science Reviews, analyzes soil from the cave to understand environmental conditions tens of thousands of years ago.

Detailed Analysis with Microstratigraphy

In previous research, the discovery of human fossils at this site, identified as 68,000 to 86,000 years old, provided the first empirical evidence for the presence of Homo sapiens in the region. This finding places the arrival of modern humans in the area chronologically in line with the oldest evidence of their presence on the Australian continent.

However, the steep accessibility of the cave, which requires specialized climbing equipment, raises questions about the mechanisms of fossil deposition. Paleontologists have hypothesized that the fossils may have been carried in by floodwaters rather than as a result of human activity within the cave. The absence of artifacts such as tools or hearth remnants in the cave reinforces this suspicion, which has become the scientific consensus in interpreting previous discoveries.

In this study, researchers led by Flinders University PhD student and Associate Professor Mike Morley of the College of Humanities, Arts and Social Sciences provide a new perspective by reconstructing soil conditions at Tam Pà Ling between 52,000 and 10,000 years ago. Using microstratigraphic techniques, they successfully identified traces of human activity in and around the cave.

Unlike conventional approaches that focus more on large-scale fossils, microstratigraphy provides a more detailed perspective on past environments. By analyzing microscopic materials such as ash and charcoal, Hernandez and his team uncovered more specific information about the environmental conditions when the oldest modern human fossils in Southeast Asia were deposited in the cave.

Environmental Changes in Tam Pà Ling

The soil analysis indicates that the environmental conditions within the cave have changed drastically over time, fluctuating between wet and dry periods. These environmental fluctuations have significant implications for the sedimentation processes within the cave, including the deposition of human fossils.

Associate Professor Morley argues that the fossils were likely carried into the cave by the flow of water from the surrounding hillsides during periods of heavy rainfall, and subsequently accumulated as sediment within the cave.

Fire Used by Early Modern Humans

The presence of a significant amount of burned material in the cave is a strong indicator of past pyrogenic activity. Possible scenarios that could explain this phenomenon include fire-making activities by early humans or wildfires in the surrounding area that carried charcoal into the cave.

Wildfires in this region would be of particular interest to those studying the fossils found there, especially since the area is currently too wet to support such fires. This suggests that the region may have been drier in the past, and the evidence of burning could provide insight into that period.

Meanwhile, if the burned material is attributed to campfires, this theory becomes even more intriguing, as it suggests that the cave held special significance for the people whose remains were found there, rather than simply being a place where their bones were washed after death. This raises the question of why people would make the dangerous journey into the cave, and encourages further investigation to uncover tools or other artifacts.