As humans spread out of Africa, an event that began, according to the most recent theories, about 120,000 years ago, they began to inhabit and adapt to different ecosystems, from the deserts of Australia to the steppes of Siberia. As Bruce Bower at ScienceNews reports, researchers long believed that humanity saved some of the world’s harshest climates for last. Evidence indicated the high-altitude eastern Tibetan Plateau didn’t see a permanent human presence until 8,000 years ago, and perhaps 12,000 to 13,000 years ago. But an archaeological dig in the region is upending that idea, with researchers unearthing tools dating back 30,000 to 40,000 years, suggesting humans were at the “Roof of the World” tens of thousands of years earlier than previously thought.

The finds came at a site called Nwya Devu. According to a press release from the Chinese Academy of Sciences, researchers previously believed the harsh habitat which has low oxygen, low rainfall and chilly year-round temperatures would have kept human colonists away. For 60 years, scientists have searched for signs of human habitation in the region, but they only found a small smattering of inhabited sites dating back to the Pleistocene, which ended 11,700 years ago, on the margins of the plateau.

So the researchers were surprised when they began finding cutting and scraping tools at the site in layers dating as far back as 40,000 years ago. In the study, which appears in the journal Science, the team reports recovering 3,683 stone artifacts in total at the site, which is located a steep 15,000 feet above sea level and roughly 185 miles north of Tibet’s capital, Lhasa. It’s believed that there were three major periods of occupation at the site, one dating 30,000 to 40,000 years ago, another 18,000 to 25,000 years ago and a third, 13,000 to 14,000 years ago. It’s believed Nwya Devu was used as a tool workshop for creating stone artifacts out of black slate found about half a mile from the excavation site. While not ideal for toolmaking, it was better than anything else in the immediate area. It’s believed the site may have also been used as a seasonal hunting camp.