Chinese geologists have revealed how and when the Central Tibetan Valley rose from a low valley to its current soaring height, providing new clues to the formation of "the roof of the world".

In a study published on Thursday in the journal Science Advances, they showed that the Central Tibetan Valley was at a relatively low elevation of 1,700 meters between 50 million and 38 million years ago, sustaining a diverse subtropical ecosystem.

It rose rapidly to become part of what is now the Qinghai-Tibet Plateau, which sits at an elevation of over 4,000 meters, between 38 million and 29 million years ago, according to the study.

Chinese and British scientists, led by Ding Lin from the Chinese Academy of Sciences' Institute of Tibetan Plateau Research, collected a large number of samples from the Lunpola Basin in the center of the valley for radiometric dating and clumped isotope analysis.

They found nine layers of volcanic tuffs there and established the absolute age of ancient sediments in the basin, thus revealing the exact point of geological transition.

The study showed that with increased elevation and the cooling of the global climate, the temperature and precipitation in the central plateau decreased significantly, with the warm-humid, low-elevation subtropical ecosystem that served as an incubator for today's Asian biodiversity giving way to a high, cold-dry alpine ecosystem.

Ding's team proposed a new model for the formation of the Qinghai-Tibet Plateau, in which the Lhasa mantle fell away and/or was thermally eroded, allowing the upwelling of the asthenosphere, a thin semifluid layer of the earth.

That process softened the crust above and facilitated the northward movement of India, finally giving rise to multiple high mountains, including the Himalayas, according to the study.