A team of Israeli researchers have concluded that early modern humans living in Qesem Cave 420,000 to 200,000 years ago heated flints by the fire before shaping them into specific tools, according to an article published on Haaretz.com
Hominins living in Qesem Cave over 400,000 years ago were happily roasting meat on open fires.
It seems they were also heating flints by – if not inside – the hearth, all-but-imperceptibly modifying the rocks and rendering them easier to shape into tools, suggests a new paper in Nature Human Behavior.
Moreover, they may have been knowingly heating rocks to different temperatures to make different kinds of tools, evincing abilities once considered to be the fief of clever Homo sapiens.
The paper by Aviad Agam, who led the research, with Ido Azuri, Iddo Pinkas and Filipe Natalio of the Weizmann Institute of Science and Avi Gopher of Tel Aviv University, is based on tools found in Qesem Cave, central Israel, which had been occupied from about 420,000 to 200,000 years ago. It has been under excavation since 2000 by Prof.
Proving that a stone was heated before being processed between 300,000 to 400,000 years ago is quite the trick. There are multiple signals: signs of soot, color change, microcracking and more. But they provide a yes/no answer, devoid of nuance.
Now the Weizmann researchers have achieved nuance, using cutting-edge technologies to analyze stone tools archaeologists had previously unearthed in the cave.
Among other things, they deduced that the different tools – blades and flakes – were made of flint heated to different temperatures, hinting at intentionality.
A new kind of human
Once upon a time, archaeologists thought that blades were so special, they could only be made by Homo sapiens, Gopher points out. Now we know that’s balderdash.
And who at Qesem was making blades and other tools with heated rocks? Not Homo sapiens; our ancestors were in their early stages of evolution in Africa.
“We don’t know exactly.
The only human bone remains found in Qesem Cave were teeth, 13 or 14 of them,” Agam tells Haaretz – and morphologically, the teeth were clearly not Homo erectus. They are more modern, showing characteristics of modern humans and Neanderthals. “It was a new type of human,” he sums up.
That early human-beyond-erectus (from which it almost certainly evolved) likely existed at the same time in other early human sites in the Levant, such as Tabun and Misliya. “But we can’t say it categorically,” Agam spells out.
“There are very few human remains in Israel from that window of time, 420,000 to 200,000 years ago.”
One is a skull fragment found in Zuttiyeh Cave, whose deceased source is known as “Galilean Man,” which doesn’t mean much – fact is, there isn’t enough in that fragment to tell what sort of human it was, Agam says.
Likely the Qesem inhabitants were “Galilean Man,” whatever that was; which in turn likely evolved from erectus in reaction to changes in environmental conditions.
What can be said is that “Galilean Man” was the first known to use fire for more than cooking meals – the first to apply pyrotechnology to making stone tools, Agam says.
The new study strongly supports the theory that the Qesem Cave occupants had achieved or did achieve control of fire and made regular use of it.
Agam is sure they could control fire – and even move it – from the day they moved into Qesem. The oldest habitation layers in the cave show they used fire all the time and could ignite it.
Nor were they the first to control fire. That skill has also been attested at the 800,000-year-old site of Gesher Benot Yaakov, though there they don’t seem to have mastered the art of heating rocks before knapping them. That is not known before Qesem.
Why a hominin would heat a rock
Elucidating whether the ancients heated flints and to what temperatures is no trivial matter.
The first step was to figure out what structural changes flint undergoes when heated.
The conundrum is all the knottier when you consider that the internal structure of rock varies from site to site depending on the geological conditions in which it forms, explains Natalio of the Weizmann Institute’s Scientific Archaeology Unit. (Note, for instance, the vast variation in the polished granite adorning kitchen countertops worldwide.)
Natalio and Agam took flints from the area of Qesem Cave and other places around Israel, heated the things to different temperatures, let them cool and analyzed them in the spectroscopy lab of Pinkas, searching for changes in chemical and molecular structure.
Much data ensued, great heaps of it, and the group tapped AI expert Azuri of Weizmann’s Bioinformatics Unit for help.
The long and short is that machine learning helped identify how heat tempered the rocks, which it did, and even what temperature range each stone had been baked in.
Bottom line: the flint from which elongated knife-like blades were fashioned had been heated to a relatively low temperature of 200 to 300 degrees Celsius (390 to 570 degrees Fahrenheit). The flint for flakes of various shapes had been heated to a median temperature of 413 degrees Celsius.
The heat at which flint evinces induced structural damage such as “pot lid” chips and microcracks is 447 degrees Celsius. At that heat, the researchers explain, bits of flint fly off the core rock of their own accord.
It’s a chicken-egg question: Did they heat rocks intentionally to improve the production of desired specific tools, or was it incidental and they realized that heated rock (in this case flint) that happened to sit by the fire is more easily knapped?
Agam acknowledges that likely the initial discovery was serendipitous.
They had fire in the cave, there were flint stones near the fire, they discovered they were easier to knapp, and a habit developed. Or maybe it began with trial and error. Of what, Haaretz inquired: what happens when you throw a rock into the fire?
No, no, no: the heart of an open fire is 400 to 500 degrees and the flint would be unhappy.
The hominins were heating the stones for processing by the fire, not inside it, Agam explains.
So: Armed with the results of Azuri and his machines, the team even speculates that the hominins knowingly heated their flints to different temperatures to create their different types of tools.
Agam helpfully explains that flakes are dead easy to make: take a rock, bang it with another rock hard enough and flakes will chip off. Making a blade, where the length is at least twice the width, requires mastery.
The Weizmann researchers did their work on samples of the tens of thousands of knapped tools, made mostly of flint, found in the context of Qesem.
The elephant not in the room
The nature of stone tools everywhere developed over time, with the advance of evolution, the environmental conditions and the available prey.
To reduce this to ad absurdum, you would need different stone tools to hunt a great hulking bison or a fleet-footed hare.
Other studies have shown that archaic hominins doted on mega-fauna, meaning big animals, as opposed to smaller animals. A favorite meal in archaic human circles of the Levant was elephant.
But by the time of Qesem, the elephant was going or had gone extinct in these parts, Agam says. The main prey of the “Galilean Man” inhabiting Qesem was fallow deer and other smaller animals, for which they needed finer tools than had been used to hunt pachyderms. Enter the blade.
“Qesem is the first appearance of systematic blade making, anywhere in the world!” Agam enthuses.
Asked if he attaches the evolution of the blade to rock heating, he avers. “This first appearance of blades has to do with their good control of fire,” he postulates. “People had used fire earlier, but at Qesem they achieved control over it at a high level.”
Natalio stresses that we cannot recreate the experience that led them to heat the “raw flint” to different temperatures, or how they managed to control the process.
“But the fact that the longer blades are consistently heated in a different way than the other pieces does point to an intent,” he says.
And as his colleague Pinkas sums up: that, dear reader, is technology, “as surely as our cellphones and computers are technology. It enabled our ancestors to survive and thrive” – even after the tasty elephant vanished and they had to shift their dietary intentions to smaller animals. For which they needed new technologies, invented by the fireside.