Ice Age people were able to survive at high elevations in the Peruvian Andes 12,400 years ago, almost a millennium earlier than previously thought, researchers said Thursday.

At an elevation of 4,500 meters (15,000 feet) above sea level, hunter-gatherers made their homes despite low oxygen, frigid weather and high solar radiation.

The discovery of tools, a rock shelter and human and animal bones at the Pucuncho archaeological site suggests that these people climbed high to settle down within 2,000 years of humans' arrival in South America.

"The Pucuncho Basin sites suggest that Pleistocene humans lived successfully at extreme high altitude," said the study in the US journal Science.

Experts still do not know if the people came to the area already well-equipped to handle extreme high altitudes, or if they evolved the traits necessary to survive and thrive.

The Andean people today show some genetic adaptations that allow them to live easier than average people at high altitudes where there is little oxygen, including a higher metabolic rate, larger lung capacity and higher hemoglobin concentrations.

"Was this adaptation present 12,400 years ago? We don't know for certain," said University of Calgary archaeologist Sonia Zarrillo, a study co-author.

However, there are signs that people were living there year-round, rather than climbing just to hunt for a few days before descending.

Remains from whole animals were found at the site, along with human skull fragments and stone tools for hunting and processing hides for clothing, blankets and other accessories.

Researchers hope to learn more about the habits of these ancient people by further studying the remote site, which remains difficult for modern hikers to access.

"Our team hiked up to three or four hours to get to these sites," said Zarrillo.

"That was a climb, carrying all of our gear, camp equipment and food. And it freezes every night. Sometimes it snows. These are incredibly hard sites to access."