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Discovery of 17 million-year-old fossilised flower adds to mystery of Tibetan plateau



October 08, 2015

Stephen Chen

Scientists found the flower at an altitude of 4,600 metres - thousands of metres above its normal living range, prompting an international team led by researchers from the mainland to calculate the plateau had risen by up to 3,000 metres since the flower was alive.

The timeline for the rise of the Tibetan Plateau is a hotly debated topic, but the discovery appears to rule out the claim by some scientists that significant growth stopped more than 20million years ago.

The collision between the Indian and Eurasian tectonic plates causes the plateau to rise a little every year, but environmental effects such as wind and rain erode some of this growth.

Many scientists had believed that the force generated by the colliding plates over the past 20 million years was not enough to outweigh the environmental erosion. Some had even argued that the plateau might have been higher in the past than today, with its present height reached as early as 50 million years ago.

But the team's discovery appears to rule this out. They believe the fossilised flower, of a Berberis plant in the Hol Xil Basin, gives an unprecedented insight into the elevation of the regional landscape at the time.

Berberis, which still thrives in Tibet, lives at altitudes between 900 and 2,500 metres - far lower than the fossil. Even allowing for the warmer climate of that period, which might have enabled the plant to live at a higher altitude, the researchers estimated the plateau must have been 2,000 to 3,000 metres lower when the plant was alive.

"Our finding does not support earlier views that northern Tibet had reached or even exceeded its modern elevation before the Miocene [23 million years ago]," wrote the team in a paper published in Scientific Reports.

They said when the plateau rose, it did so relatively quickly. "The elevation of northern Tibet probably remained stable from the Eocene [more than 50 million years ago] to early Miocene [23 million to 5 million years ago] but since then there has been a considerable uplift," they said. The team was led by professor Wang Yufei and Li Chengsen of the Chinese Academy of Sciences' Botany Institute.

Wang Jiangang, associate researcher with the academy's Institute of Geology and Geophysics, said the study provided new and valuable information.

"It is commonly accepted that the Tibetan Plateau stopped growing at some point, but when exactly that happened remains a hot debate," said Wang Jiangang, who was not involved in the research. The debate has led to the development of ingenious methods to calculate the plateau's rise, such as measuring lightweight oxygen isotopes in sediment.

"The plant fossil provides a good angle to look at the issue, but the method has its limits - such as possible natural transportation of the plant before burial," Wang Jiangang warned.

Even so, he added, "[their] result can be trusted if it matches the findings of other methods".

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