The 12,400-year-old settlement was found in a cave called the Cuncaicha rock shelter, located nearly 4,500 metres above sea level. That makes it the highest ice age human settlement ever found.
The site is more than 2,000 metres higher than the famous Inca archeological site Machu Picchu — where travellers already risk becoming ill from altitude sickness — and just 880 metres lower than the Mount Everest base camp in the Himalayas.
The discovery, published online Thursday in the journal Science, suggests that just 2,000 years after arriving in South America, humans had already spread into some extreme environments.
"High altitude was not a barrier to human colonization at least by 12,400 years ago," said Sonia Zarrillo, an adjunct assistant professor of archeology at the University of Calgary, who co-authored a study describing the discovery.
The harsh environment made it a challenging project for the international research team, who braved headaches and exhaustion from low oxygen, freezing temperatures and rugged camping conditions to complete their work.
"This was the hardest archeology I've ever done," Zarrillo said.
Kurt Rademaker, lead author of the study, stumbled upon the Cuncaicha cave while looking for a place to camp for the night during research for his PhD thesis a few years ago. Rademaker "instantly recognized that it was an archeological site," Zarrillo added.
At the time, Rademaker, now a visiting assistant professor of anthropology at the University of Maine, was trying to find out where a mineral called obsidian found at archeological sites on the Peruvian coast may have come from.
Excavations at the Cuncaicha rock shelter, which was big enough to fit 20 or 30 people, revealed that it had been occupied multiple times over thousands of years.
So far, the artifacts recovered include scrapers, tools used to process animal hides so they could be used to make things like clothing and tents. Zarrillo said that is good evidence that people stayed at the settlement for long periods of time.
"We do tend to think that this was family groups that were there, not just men going up hunting and bringing meat back."
She added that the soot-blackened walls of the cave suggest that campfires burned inside for long periods of time, and there was lots of charcoal and bones from llama-like vicunas and guanacos at the site: "They were sure eating a lot of meat."
The cave is located in a cold and dry area of the Andes that Zarrillo describes as "a moonscape."
"Today if you just saw a picture of the site, you would say, 'Who the heck would want to come up here and why?'"
But the nearby Pucuncho Basin appears to have been a rich, moist hunting ground for animals such as vicunas and guanacos 12,000 years ago, when the climate was just a little bit cooler and wetter.
Today, the area is used by local Andean herders to graze thousands of llamas and alpacas. The locals have genetic adaptations that allow them to live comfortably at high altitude, such as unusually large lung capacities, high metabolic rates and the ability to carry more oxygen in their blood. Those adaptations were thought to have taken thousands of years to evolve.
The fact that humans were living at these altitudes for long periods of time just 2,000 years after entering South America raises scientific questions.
"Other people have suggested that people could not and did not live at those elevations prior to genetic adaptations occurring," Zarrillo said. "What we're showing is either they were genetically adapted to living up there or it didn't matter."
Zarrillo specializes in identifying edible plants at archeological sites. There are no edible plants growing in the area surrounding the Cuncaicha cave. Nevertheless, Zarrillo found bits of edible roots and tubers from lower elevations. That suggests the Cuncaicha cave dwellers were either trading with other groups or moving to lower elevations at some times of the year.
In the future, the researchers want to learn more about how the ancient cave dwellers interacted with people at other altitudes.
They also hope to be able obtain human remains with DNA from the cave that can be tested for signs of genetic adaptation to high altitude.
In addition, Zarrillo said, it's possible that there are even older settlements in deeper layers of the cave floor or other sites in the area.