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Amazon River Formed 11 Million Years Ago, 3-Mile Sediment Core Reveals

This post is part of a special National Geographic news series on global water issues.

The Amazon River originated as a transcontinental river around 11 million years ago and took its present shape around 2.4 million years ago, European researchers said yesterday.


Amazon River mouth picture courtesy NASA

The finding was based on analysis of two boreholes drilled near the mouth of the planet’s largest river by Petrobras, the national oil company of Brazil.

One of the boreholes was nearly 3 miles deep (4.5 kilometers), allowing the scientists to get a look at the sediment that has accumulated on the ocean floor near the mouth of the river over millions of years.

Amazon-River-picture-2.jpgA team formed by the Institute for Biodiversity and Ecosystem Dynamics of the University of Amsterdam, the University of Liverpool and Petrobras used the new oceanic record provided by the drilling core to reconstruct the history of the Amazon. The study was published in the July 2009 issue of the academic journal Geology.

NGS photo of Amazon River by Winfield Parks

“Until recently the Amazon Fan, a sediment column of around 10 kilometres [around 6 miles] in thickness, proved a hard nut to crack, and scientific drilling expeditions such as Ocean Drilling Program could only reach a fraction of it,” the University of Amsterdam said in a statement.

“Recent exploration efforts by Petrobras lifted the veil, and sedimentological and paleontological analysis on samples from two boreholes, one of which [was] 4.5 kilometres below sea floor, now permit an insight into the history of both Amazon River and Fan.

“Prior to this publication the exact age of the Amazon River was unknown.

“This research has large implications for our understanding of South American paleogeography and the evolution of aquatic organisms in Amazonia and the Atlantic coast. It is a defining moment as a new ecosystem originates which at the same time forms a geographic divisor,” the university added.

Sediment aprons in the proximity of major rivers often hold continuous records of terrestrial material accumulated by the river over time. These records provide a unique insight into the historic climate and geography of the land, , the university said. 

“The information released from this 4.5 kilometre borehole is a scientific breakthrough and stresses the value of cooperation between academia and industry.”

More from National Geographic News:

Amazon River Once Flowed Other Way, Study Says

Amazon Longer Than Nile River, Scientists Say