The discovery of 3,600 stone artifacts in Tibet’s high plateau suggests humans inhabited one of the earth’s harshest environments far earlier than previously thought.

According to a paper published this week in Science magazine, a team of researchers from the Chinese Academy of Sciences says humans first set foot on the interior of the Qinghai-Tibetan Plateau around 30,000 to 40,000 years ago, which is some 20,000 years earlier than previously believed.

Most archeologists contended that humans first set foot on the plateau about 20,000 or 30,000 years ago but did not settle permanently until 6,000 or 7,000 years ago.

According to archeological evidence, the region is one of the last habitats colonized by Homo sapiens, which is not surprising considering the harsh conditions.

“The high altitude, atmospheric hypoxia, cold year-round temperatures and low rainfall of the plateau creates an extremely challenging environment for human habitation,” according to a press release.

Stone artifacts on the surface. (Institute of Vertebrate Paleontology and Paleoanthropology )

The plateau is known as the “roof of the world” and still remains the third least-populated place on Earth.

The team confirmed the timeline after finding stone artifacts at the Nwya Devu Paleolithic site located 15,000 feet above sea level in the Changthang region of northern Tibet.

The artifacts discovered were buried undisturbed underground, reliably confirming their age.

“It really is the first robust case to be made that there were human populations on the high plateau,” Jeff Brantingham, an archaeologist at the University of California, Los Angeles, who studies the peopling of the Tibetan Plateau but was not involved with this study, told National Geographic.

Interestingly, no DNA was found on the stone tools so it is difficult to determine who made them.

“The authors used the word ‘Tibetan’ a lot, and they act as if the people they’re looking at are in fact Tibetans — they’re not,” National Geographic explorer Mark Aldenderfer, an archaeologist at the University of California, Merced, told the magazine. “We don’t know who these people were.”

Some studies indicate most modern Tibetan ancestry traces back to a population that separated from the Han Chinese roughly 9,000 years ago.

The archaeologists at the Nwya Devu say the tools are nearly identical to tools recovered from Mongolia and Xinjiang.

The site is about 186 miles northwest of Lhasa, the capital of Tibet Autonomous Region, and is the oldest and highest early Stone Age (Paleolithic) archaeological site known on Earth.