This is a scientific American 60 second science. I'm Cynthia Graber. Got a minute?

The Tibetan Plateau at an altitude of some 3,000 meters above sea level is often called the roof of the world.

Some prehistoric people tried living there starting about 20,000 years ago.

Remains of cooked animals and small-scale hearths show that a few hardy souls did give the

harsh region a go, at least temporarily, but they did not stick around.

Permanent human settlements in the area began about 5,200 years ago,

so scientists wanted to know what changed.

Researchers collected artifacts, animal bones, and So scientists wanted to know what changed.

Researchers collected artifacts, animal bones, and plant remains from 53 sites.

The oldest camps only reached altitudes of about 2,500 meters, and at these sites,

Millet makes up 98% of dietary grain.

But about 3,600 years ago, a new kind of barley arrived in the region

after being domesticated in the fertile crescent that spread from the Persian Gulf to the Nile.

The new barley tolerated frost and had a longer growing season, which means it grew above the 3,000

meter mark and that people could settle there.

Diets at those heights became dominated by the new hardy barley.

The findings are in the journal Science.

The researchers say that the cross-cultural grain exchange from the fertile crescent

thus appears to be what allowed humans to finally reach the roof of the world.

Thanks for the minute. For Scientific American 60 Second Science, I'm Cynthia Graber.