Buried in Arnhem Land, an ancient fire trick may rewrite early stone technology's timeline

06 May 2026, 16:40 by Sandee Oster

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Heat-treated chert from Nauwalabila I and microscopic views of roughness contrast. Non-labeled surfaces are relatively smooth post-heating surfaces. Chert is dated to between 0.29±0.06 and 13.5±0.9 ka BP by thermoluminescence. Credit: Schmidt and Hiscock 2026

A recent archaeological study has identified the earliest lithic heat treatment of chert in the world. Discovered in Australia, this discovery is nearly twice as old as any previously identified chert heat treatment in Eurasia. The study is published in the Journal of Paleolithic Archaeology.

Heat treating stone

H. sapiens have been heat treating stone since the Pleistocene, with the earliest evidence of heat treatment of silcrete coming from Africa between 120 ka and 164 ka. Meanwhile, chert heat treatment was supposedly developed much later, with early evidence stemming from Dyuktai (~25 ka) and the European Solutrean (~22 ka).

However, heat treating silcrete is much easier compared to chert, as it is less prone to combustion and can be placed directly in or near a campfire. Chert, on the other hand, being a marine rock, traps more moisture with less ability for that moisture to escape during heating, making it more prone to combustion when not heated properly.

Pleistocene H. sapiens heat-treated these minerals in order to help with knapping. With chert in particular, this treatment helps with the production of flakes and blades, Dr. Patrick Schmidt, lead author of the study, explained.

"The transformations taking place in chert during heat treatment cause the formation of new atomic bonds within and between the individual crystals of the rocks. This leads to the loss of pore space, allowing better force transmission when a fracture runs through the material. In terms of stone knapping, this means that less force is needed to make flakes and blades."

The archaeological site of Nauwalabila

Evidence of heat treatment in Australia has been documented for at least 40 ka, with silcrete generally being the rock of choice across the continent, including during the late Pleistocene and Holocene, when other parts of the world had generally shifted towards heat treatment of chert.

That assumption was overturned when Dr. Schmidt and Dr. Peter Hiscock, co-author of the study, reanalyzed lithic assemblages from two roughly contemporaneous sites in Arnhem Land.

Nauwalabila was first excavated in 1981 and has an early occupation dated to around 68–48 ka. Interestingly, it yielded a rich assemblage of chert but was devoid of silcrete, whereas the roughly contemporary Madjedbebe yielded abundant silcrete but no chert.

Chert artifacts from the Nauwalabila I show distinct roughness contrasts, differentiating pre-heating surfaces from smooth post-heating surfaces. Credit: Schmidt and Hiscock 2026

During analysis, it was found that the chert at Nauwalabila had been heat-treated with these artifacts, dated to at least 45–40 ka and possibly as old as 60 ka, making them the oldest evidence of chert heat treatment in the world. Additionally, they observed that lithics were knapped both before and after heating, indicating that the chert heating was likely intentional, as the heated stones were re-knapped after heat exposure.

Innovation of heat treatment of chert

However, this raised a few questions. The first being, was chert heat treatment an independent invention in Australia? The problem with this hypothesis is that chert is more difficult to transform than silcrete, creating a significant innovation gap if simple heat-treatment technology was not already in place by the time H. sapiens arrived in Australia and began chert heat treatment.

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The second hypothesis is that knowledge of heat treatment, including chert, may have spread to Australia with early colonists as they dispersed through South and Southeast Asia. These areas are rich in chert but poor in silcrete, meaning earlier chert heat treatment should be evident along these early migration routes, but has yet to be found.

According to Dr. Schmidt, the absence of such evidence is "probably due to the lack of systematic research on heat treatment in South and South-East Asia. In the past, archaeologists have not specifically looked for heat-treated artifacts in these regions. The Dyuktai and Solutrean are not the way people would most likely have taken to reach Australia after leaving Africa.

"Their significantly younger ages are therefore not really relevant to what happened during the spread of early Homo sapiens. Only future research that is specifically looking for heat-treated chert will help resolve these open questions."

If the hypothesis holds, the Nauwalabila heat-treated chert should provide a minimum age for when knowledge of heat treatment was transferred from silcrete to chert.

Major heat-treatment sites for stone tools in Australia show a distinct geographic split. Red= Chert, Blue= silcrete. Credit: Schmidt and Hiscock (2026) adapted from Taylor and Eggleton (2017) and Wallen Wallen Creek data (Adams et al. 2024).

Additionally, the discovery may help explain the distribution of heat-treated materials across Australia, with chert treatment dominating in the north, where colonists first arrived, and where the local geology is chert-dominated, while in the south and southeast, silcrete heat treatment is more widely distributed, likely due to the more silcrete-abundant landscape.

Future studies will likely focus on increasing the resolution of heat treatment sites, Dr. Schmidt explained. "I think the next step should be to obtain a better resolution of chert and silcrete heat treatment in Australia by conducting studies at different sites across the continent."

Additionally, he added that, "Outside of Australia, we are in need of systematic studies aiming at identifying potentially heat-treated artifacts in South Asia and insular South-East Asia."

Written for you by our author Sandee Oster, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.

More information

Patrick Schmidt et al, Earliest Lithic Heat Treatment in Australia is the World's Oldest Known Treatment of Chert, Journal of Paleolithic Archaeology (2026). DOI: 10.1007/s41982-026-00262-5