“We need to rethink when hominins first left Africa,” said Robin Dennell, an archeologist at the University of Sheffield and one of the authors of the paper. “We have shown that the earliest evidence from outside Africa is at least 2.1 million years old, and therefore 250,000 years—or 10,000 generations—older than Dmanisi in Georgia.”

“It’s so old that the earliest members of our own genus, the genus Homo, may have migrated out of Africa,” said Michael Petraglia, a professor of anthropology at the Max Planck Institute who was not involved in the new study. These creatures would have likely been Homo erectus; or possibly even Homo habilis, the first ancient primate to be called Homo.

Petraglia emphasized that the discovery also changes our understanding of Ice Age China. “They’ve added on something like 400,000 years of prehistory [in East Asia]—and it’s not every day you get to do that,” he told me. “Some of the oldest sites in China were previously only 1.6 or 1.7 million years old. They’re now saying the oldest sites are 2.1 million years old.

The research was led by Zhaoyu Zhu, an archeologist and climatologist at the Chinese Academy of Sciences. Zhu and his team have spent the past 13 years excavating a unique site on China’s Loess Plateau, a rare spot protected from erosion and glaciation, and continually buried in wind-blown sand over the past several million years.

While the new paper identifies a human presence, the researchers have not yet found any early-human fossils at the site. They have unearthed a wealth of early stone tools left behind by our ancestors, buried under many layers of solidified sand. These artifacts are mostly chipped flakes of stone, a type of primitive blade created by smashing two river-smoothed cobbles together. Hominins in Africa are known to have used this technology during the same period.

Claiming an ancient-human presence from a bunch of stone flakes could prove controversial among some researchers, who only feel confident dating an ancient-human presence when they find the remains of an early human, like teeth, a jaw bone, or ancient DNA.

But both the paper’s authors and outside experts told me they felt comfortable asserting that ancient humans lived on this site.

“It comes down to two general points,” said John Kappelman, a professor of anthropology and geology at the University of Texas at Austin who was not connected to the research. First, the stone tools “look like they were produced by humans,” he told me. They also show evidence of manufacture and maintenance. Some flakes have an almost serrated edge, suggesting that their creator smashed them against a cobble multiple times in order to improve them. Others “appear to show resharpening or sharpening,” he said, meaning their users attended to their tools and tried to improve them.