Ancestral humans created a style of tools known as Acheulean around 1.5 million years ago. Eventually, both the technology and the species responsible disappeared. The discovery of Acheulean handaxes on the Arabian Peninsula in 190,000-year-old soil layers marks easily the most recent examples of these tools we have found. What makes this find really intriguing is that the date brings Acheulean technology tantalizingly close to overlapping with the first Homo Sapiens outside Africa.
When modern humans spread out of Africa we were not the first members of the genus Homo to tread that path. Neanderthals had been living in Europe and western Asia for 300,000 years, and Homo erectus had been more widespread for far longer. These early humans brought with them their own technology, of which Acheulean tools are among the most important examples. Since stone tools survive the ages better than bones or teeth, they frequently provide evidence of human presence where we have no fossils to tell us about their makers.
Central Saudi Arabia has a harsh climate today, but like the rest of the mid-latitude arid belt, had periods during the Pleistocene where it was dotted with rivers and lakes. Humans followed the waterways in these times, including to Saffaqah, where many geological layers contain Acheulean tools. Dr Eleanor Scerri of the Max Planck Institute for the Science of Human History has obtained dates for some of these layers for the first time, currently the only dates for Arabian Acheulean remains.
In Scientific Reports, Scerri provides evidence of occupation of Saffaqah by Acheulean toolmakers around 280,000 and 190,000 years ago. The dates are unexpectedly recent, since in the better-studied Levant similar tool styles date from 1.5 million years to 300,000 years ago.
There were two layers containing tools above the youngest Scerri tested, indicating Acheulean tools were being used even more recently. Scerri told IFLScience the team focused on the best-preserved layers, but now they know how recent the well-preserved layers are, they're very keen to date the younger tool-containing ones.
The most important finding would be if the most recent tools overlap with the time when modern humans reached Arabia, indicating likely encounters between different human species. Scerri told IFLScience: “The earliest migrations out of Africa are typically thought to have taken place around 125 thousand years ago – another period of greening in the Sahara.”
While modern humans are thought to have outcompeted the Acheulean tool-makers, Scerri said the records suggest slow decline and fragmentation, rather than a sudden collapse as would occur if it was all a new competitor's fault. “So it's really not as simple as 'one hominin species wiping out another',” she said.
Saffaqah was not just a living place for early humans, but a site of tool manufacturing. Scerri and her colleagues found 500 handaxes and stone cleavers. This was small compared to the thousands of previous expeditions collected, but Scerri also observed stone flakes used in tool making resting on the rocks from which they had been struck. Not only does this prove the tools were made on site, but how intact the layers are.
"It is not surprising that early humans came here to make stone tools," Scerri said in a statement. "The site is located on a prominent andesite dyke that rises above the surrounding plain. The spot was both a source of raw material as well as a prime location to survey a landscape that, back then, sat between two major river systems.”