The Tibetan plateau, also known as the "roof of the world," sits, at a minimum, a mile and a half above sea level. It wasn't until about 3,600 years ago that anyone settled in those sky-high locations, the New Scientist reports. The key to making that move, according to new evidence, was barley.
Researchers from China, the U.S. and the U.K. arrived at this conclusion after analyzing ancient grain samples collected at 53 sites in and around the Tibetan plateau at a variety of elevations. They used radiocarbon dating to figure out how old the samples were. According to those investigations, around 3,600 years ago, ScienceNOW reports, people suddenly began populating significantly higher elevations than before. Around the same time, barley began popping up in those ancient archeological sites.
This makes sense: unlike millet, barley is quite cold and frost tolerant. For the first time, people could survive a freezing winter at high altitude without starving. As ScienceNOW explains, "the high-altitude farmers appear to have abandoned millet altogether and relied almost completely on the new, hardier grain."
The researchers told the New York Times that barley seeds probably first arrived in the area alongside sheep and wheat. The time of that arrival coincides with a mass movement of crops around the world, with African crops expanding into South Asia, the New Scientist elaborates, and various Asian crops being brought to new parts of the continent and to the Middle East. Eventually, those crop swaps evolved into a more well-established trade route: the Silk Road.