Scientists have discovered the oldest evidence of ancient humans igniting fires: a 400,000-year-old open-air hearth buried in an old clay pit in southern England.
The study, published in the journal Nature, is based on a years-long examination of a reddish patch of sediment excavated at a site in Barnham. It pushes back the timeline on fire-making by about 350,000 years.
The nebulous question of how far back human ancestors conjured fire is deeply intertwined with some of the biggest outstanding mysteries about human evolution. The ability to reliably set fires would have allowed humans to cook food, expanding the range of what they could eat and making meals more digestible. That, in turn, could have supported bigger brains that consumed more energy, catalyzing new social behaviors as humans gathered around campfires.
But campfires don’t leave fossils. It takes painstaking work to reconstruct these ephemeral uses of technology. And what remains unclear is who set them. No telltale bones have been recovered at Barnham, but researchers think it was Neanderthals, close cousins of our species who interbred with our ancestors.
“The evidence of fire is incredibly difficult to preserve. If you get to ash and charcoal, it can wash away. Sediment can get washed away,” said Nicholas Ashton, curator of Paleolithic collections at the British Museum and one of the leaders of the work. “We just found this one pocket — quite a large site — where it happens to be preserved.”
Even when traces of fire remain, the task of distinguishing incidental flames sparked by lightning strikes or wildfires from those set by people is difficult. Perhaps most challenging is distinguishing between fires ignited by humans with the know-how from those produced by scavenging embers from wildfires.
The study could spark more debate.
“The authors did an excellent job with their analysis of the Barnham data, but they seem to be stretching the evidence with their claim that this constitutes the ‘earliest evidence of fire making,’” Wil Roebroeks, an archaeologist at Leiden University, said in an email, calling the evidence “circumstantial.”
Ségolène Vandevelde, an archaeologist and adjunct professor at the University of Quebec at Chicoutimi, praised the multidisciplinary approaches the authors used and said the finding was “solid.”
Pyroarchaeology
In the Paleolithic era, the Barnham site would have been a woodland with a seasonal pond — set away from the main river valley, where predators might have roamed, according to Robert Davis, an archaeologist at the British Museum and one of the authors of the study. The wildlife would have included elephants, lions, deer, fish and other small mammals.
Despite the fleeting nature of fire, it can leave traces under the right conditions. At the site in Barnham, where artifacts such as heat-shattered flint hand axes were also found, researchers were intrigued by a layer of reddish sediment — a result of iron-rich sediments being heated to produce a mineral called hematite. For four years, they studied it, trying to determine whether it was the result of a wildfire or deliberate human activity.
One of the first questions they asked was whether this was a one-time blaze or something closer to a fireplace that was lit and relit many times.
To deconstruct this question, scientists studied the magnetism of the sediment, which is altered by heating. They conducted modern experiments, to see if they could come up with an estimate of how many heating events might have resulted in the magnetic profile of the sediment — and found that after about a dozen heating events, each one four hours long, their modern samples mimicked the archaeological one.
Then they examined the chemistry of the site — scrutinizing particular chemical compounds left behind. The patterns they found suggested humans had been using these fires.
The last element was small pieces of cracked flint scattered about the site — as well as two bits of pyrite, which can create a spark when struck together. A geological study of the area showed that pyrite was scarce in the local landscape, leading the authors to argue that the inhabitants had carried it there for the specific purpose of making fire.
Scavenging sparks vs. setting fires
The archaeological record with examples of fires used by hominins — the ancestors of humans — stretches back more than a million years ago in Africa.
But what interests scientists is not just the ability to successfully scavenge sparks from wildfires or lightning strikes, but also the ability to reliably create it — possibly by striking flint and pyrite together to create sparks.
The oldest accepted evidence of fires purposefully set are from a Neanderthal site dated to 50,000 years ago in France. That evidence is considered convincing in part because there are chunks of flint showing “microwear traces of having been struck” to create sparks, Roebroeks said. But at Barnham, there are no microwear traces, leaving room for disagreement.
“It’s a very contentious debate that’s been going on for some time,” Davis said.
Early hominins would have learned to harvest fire by collecting embers, harvesting the right fuel and tending the fire. And eventually, they had to learn how to make it on demand — which would allow them to live in colder places, cook, fend off predators and socialize after dark.
The study does not suggest that Barnham was where fire originated; it was probably widespread across the ancient world. But it does offer a rare, preserved snapshot of prehistoric life.
“The maintenance of fire requires social cooperation, cultural rules and work coupled with knowledge of wood types, and means that a complicated tradition is at play,” said John Hawks, a paleoanthropologist at the University of Wisconsin at Madison.
