Fossils and fires: Insights into early modern human activity in the jungles of Southeast Asia

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Studying microscopic layers of dirt dug from the Tam Pà Ling cave site in northeastern Laos has provided a team of Flinders University archaeologists and their international colleagues with further insights into some of the earliest evidence of Homo sapiens in mainland Southeast Asia.

The site, which has been studied for the past 14 years by a team of Laotian, French, American and Australian scientists, has produced some of the earliest fossil evidence of our direct ancestors in Southeast Asia.

Now a new study, led by Ph.D. candidate Vito Hernandez and Associate Professor Mike Morley from the College of Humanities, Arts and Social Sciences, has reconstructed the ground conditions in the cave between 52,000 and 10,000 years ago. The work appears in Quaternary Science Reviews.

"Using a technique known as microstratigraphy at the Flinders Microarchaeology Laboratory, we were able to reconstruct the cave conditions in the past and identify traces of human activities in and around Tam Pà Ling," says Hernandez. "This also helped us to determine the precise circumstances by which some of the earliest modern human fossils found in Southeast Asia were deposited deep inside."

Microstratigraphy allows scientists to study dirt in its smallest detail, enabling them to observe structures and features that preserve information about past environments, and even traces of human and animal activity that may have been overlooked during the excavation process due to their minuscule size.

The human fossils discovered at Tam Pà Ling were deposited in the cave between 86,000–30,000 years ago, but until now, researchers had not conducted a detailed analysis of the sediments surrounding these fossils to gain an understanding of how they were deposited in the cave or the environmental conditions at the time.

The findings reveal that conditions in the cave fluctuated dramatically, going from a temperate climate with frequent wet ground conditions to becoming seasonally dry.

"This change in environment influenced the cave's interior topography and would have impacted how sediments, including human fossils, were deposited within the cave," says Associate Professor Morley.

"How early Homo sapiens came to be buried deep within the cave has long been debated, but our sediment analysis indicates that the fossils were washed into the cave as loose sediments and debris accumulating over time, likely carried by water from surrounding hillsides during periods of heavy rainfall."

The team also identified preserved micro-traces of charcoal and ash in the cave sediments, suggesting that either forest fires occurred in the region during the drier periods, or that humans visiting the cave may have used fire, either in the cave or near the entrance.

"This research has allowed our team to develop unprecedented insights into the dynamics of our ancestors as they dispersed through the ever-changing forest covers of Southeast Asia, and during periods of variable regional climate instability," says study co-author Assistant Professor Fabrice Demeter, paleoanthropologist from the University of Copenhagen, who has been leading the team of international researchers studying Tam Pàn Ling since 2009.

More information: Late Pleistocene–Holocene (52–10 ka) microstratigraphy, fossil taphonomy and depositional environments from Tam Pa Ling cave (northeastern Laos), Quaternary Science Reviews (2024).

Journal information: Quaternary Science Reviews

Provided by Flinders University