Scientists have discovered how ancient people hardened stone tools

Important: we are not talking about "hardening" in the sense of metal working. Ancient people did not melt the stone, but gently heated it to change its internal properties and make it easier to split.

Details

The study concerns the Nauwalabila I site at Arnhem Land in northern Australia. It is one of the oldest archaeological sites on the continent. Scientists have re-examined stone artefacts from the site and found indications that some of the flint was deliberately heated before further processing.

This was the technique used to make stone splinters and blades. Once heated, flint changes its structure: it better transmits the force of impact, so it is easier to break off thin and sharp fragments. Simply put, the fire helped to make the stone more "docile" to the master.

Flint is more difficult to work with fire than some other rocks, such as Silcrete. It can retain moisture and can crack or deteriorate if heated improperly. Therefore, this technology required experience: the stone had to be heated hard enough, but not to spoil it.

The age of the finds is particularly important. According to the authors, the heat treatment of flint at Nauwalabila I is definitely older than 45-40 thousand years, and according to some interpretations it may date back to the period of 60-53 thousand years ago. This makes it the oldest known example of such flint processing in the world.

The scientists also saw that the stones were worked both before and after heating. This is an important sign of intentionality: people didn't just casually throw a stone into a fire, but used fire as part of the tool-making process chain.

Why it matters

The finding shows that the ancient inhabitants of Australia had a very early mastery of sophisticated technological techniques. They didn't just select the right stone, they altered its properties using fire.

This discovery also changes the chronology of early stone technology. Previously, ancient examples of flint heat-treatment were more often associated with later monuments in Eurasia - for example, around 25,000 years ago in the Duktai region and around 22,000 years ago in the European Solutre. The Australian find is almost twice as old as these examples.

At the same time, earlier heat treatment of other rocks is known in Africa: silkcrete was heated there as early as about 120-164 thousand years ago. Therefore, the discovery from Australia does not mean the first use of fire for processing stone at all. Its significance lies elsewhere: it is the earliest reliable example of flint working specifically.

Background

Archaeologists debate how such technology came to Australia. One possibility is that it may have been independently invented locally. Another is that the first Homo sapiens may have brought knowledge of stone heat treatment with them as they travelled from Africa and West Asia through South and Southeast Asia.

There is no definitive answer yet. If the technology came with the early migrants, archaeologists should find similar traces of flint heat-treatment on routes through South and Southeast Asia. The authors note that such finds may simply not have been systematically searched for.

In Australia itself, the picture is not uniform either. In the north, where flint is abundant, early traces are associated with it. In the southern and south-eastern regions, silcrete working is more common, probably because of the availability of this material.

Source

Patrick Schmidt and Peter Hiscock Earliest Lithic Heat Treatment in Australia is the World's Oldest Known Treatment of Chert published in the Journal of Paleolithic Archaeology in 2026. The authors studied artefacts from Nauwalabila I in Arnhem Land and concluded that it is the oldest known example of systematic heat treatment of flint.