A study of ancient life on the Tibetan Plateau — the so-called roof of the world — says it was the ability to grow barley that allowed humans to establish permanent settlements at very high altitudes.

Archaeologists collected stone artifacts and charred plant remains from 53 sites across the northeastern plateau to learn how humans came to live at high altitudes. Their findings showed that people established year-round settlements as high as 2,500 meters above sea level (about 8,200 feet) starting around 5,200 years ago. But the settlers subsisted largely on frost-sensitive grains that would not have thrived at higher altitudes.

The first settlements above 3,000 meters (nearly 10,000 feet) appeared about 3,600 years ago, and show evidence of hardier grains: mostly barley, plus some wheat and broomcorn millet, said the study, which was published in the journal Science.

“As barley is frost hardy and cold-tolerant, it is growing very well on the Tibetan Plateau even today,” Fahu Chen, an archaeologist at Lanzhou University in China and the lead author of the study, wrote in an email. “Barley agriculture could provide people with enough sustained food supplies even during wintertime.” The grain was introduced to the area “around 4,000 years ago alongside with wheat and sheep.”