Study: Amazon River is at least 9 million years old

According to new research, the Amazon River is between 9 and 9.4 million years old. Estimates that the river is considerably younger are wrong, scientists say.

Researchers at the University of Amsterdam and the University of Brasilia analyzed sediments from an offshore borehole drilled for oil and gas exploration. Their findings revealed a shift in sediment composition and plant debris during the late Miocene, between 9 and 9.4 million years ago, suggesting a change in the source of the river from the tropical lowlands to the peaks of the Andes.

Scientists have previously suggested the Amazon was as young as 1 to 1.5 million years old.

"We were able to narrow down the age of onset of the Amazon River because we sampled the transition interval in a classical section of the Amazon submarine fan, where the sediments transported by this river are deposited and as a result accurately record its evolutionary history," former Brasilia researcher Farid Chemale, now a professor at Unisinos University, said in a news release. "We applied high resolution analytical techniques not previously performed in the region."

Samples collected from the borehole showed a dramatic increase in grass matter, suggesting regional climate change over the last 2.5 million years has significantly affected plant composition in the Amazon.

"The changes detected in the sediment record lead to the tantalizing question of whether the Amazon region might have changed dramatically during Plio-Pleistocene global cooling," said Carina Hoorn, a researcher at the UvA's Institute for Biodiversity and Ecosystem Dynamics. "Our new data confirm an old age for the Amazon River and also point at an expansion of grasslands during the Pleistocene that was not known before."

Researchers published their findings in the journal Global and Planetary Change.