The tools are so old that they couldn’t possibly have been made by Homo sapiens, and with no hominin bones from the site, it’s unclear which species created the objects. Still, “it’s extremely provocative evidence,” says Eleanor Scerri, an archaeologist from the University of Oxford who was not involved in the study. The artifacts suggest that hominins were in North Africa, carving up animal meat, at least 600,000 years earlier than previously thought. More importantly, they suggest that the Oldowan culture—the earliest well-accepted stone technology—either spread from East Africa to the north very quickly or originated in different parts of Africa independently.

“It highlights North Africa, and the Sahara in particular, as a major region of importance in the evolutionary processes leading to our own species,” Scerri says. “Sahnouni and his colleagues have been working in that area for many years, and I really salute their persistence.”

Sahnouni has been working in the Algerian High Plateaus since the 1980s, and he uncovered the tools and bones of Ain Boucherit around a decade ago. But finding artifacts is often the easiest bit of archaeology. “The real issue was how to date them in a way that would convince the scientific community,” Sahnouni says.

The geology of the Algerian plateaus is such that many widely used and highly accurate dating techniques can’t be utilized there. Instead, the team relied on the fact that Earth’s magnetic field has repeatedly flipped throughout the planet’s history. Those inversions leave telltale signals within rocks. By comparing the magnetic signals from Ain Boucherit against a well-established global calendar, the team could work out how old any part of their site was—including the layers that yielded the bones and tools.

The animal bones also provided clues. Many of them came from species of extinct pigs, horses, and elephants that only lived within certain time frames, which the team checked against the dates from their magnetic calendar. This work, which took most of the decade to do, revealed that the two areas the team dug up were 1.92 million years old and 2.44 million years old.

There are two ways of interpreting these dates, Sahnouni says. First, it’s possible that the same hominins who made the East African Oldowan tools 2.6 million years ago rapidly spread to the northwest, covering more than 3,000 miles in about 150,000 years. To Sahnouni, that seems unlikely. “It’s not like they just decided to get to the north and started walking,” he says. The intervening land “wasn’t easy to go through, and they would have had to look for food and resources. That takes time.”

The explanation he favors is that early stone tools, and perhaps even the hominins who made them, evolved independently in different parts of Africa—in the east, northwest, and perhaps elsewhere. There’s other evidence for this. For example, the oldest known hominin is 7 million years old, and was found in Chad, about 1,900 miles west of the rich finds in East Africa. “That was a turning point in rethinking the origin of humans in only East Africa,” says Sahnouni, who is confident that work in other parts of Africa will upend the narrative even further.