News in Brief: Yangtze's age revealed

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http://www.sciencenews.org/view/generic/id/349900/description/News_in_Brief_Yangtzes_age_revealed




The world’s third longest river has a new age: The Yangtze River was in place by at least 23 million years ago, geologists report April 22 in the Proceedings of the National Academy of Sciences.

The Yangtze stretches for 6,300 kilometers across China, from the Tibetan Plateau to the East China Sea. Geologists have debated the river’s age for more than a century, with estimates ranging from 2 million to 45 million years old.

A team led by Hongbo Zheng of Nanjing Normal University in China investigated the Yangtze’s antiquity by studying rocks in the Jianghan Basin, which the river flows through downstream of the Three Gorges Dam. The researchers found rocks there that appear similar to the river’s modern sediments and dated them to roughly 23 million years ago. Older sediments — which can’t form in the presence of flowing water — put an upper limit on the Yangtze’s age of 36.5 million years.

The researchers say the timing of the Yangtze’s birth corresponds with changes in China’s topography caused by the uplift of the Tibetan Plateau. Asia’s summer monsoon rains also intensified around that time, which would have fed the fledgling river.