A new study, published in the journal Geology, estimates the age of the Amazon river at 11 million years.
Conducting analysis of sedimentological and paleontological data obtained by drilling deep boreholes (up to 4.5 kilometers or 2.8 miles deep) near the mouth of the Amazon, a team of scientists from University of Amsterdam, the University of Liverpool and the Brazil’s national oil company Petrobras constructed a historical record for Earth’s mightiest river.
The researchers found the Amazon River originated as a transcontinental river some 11 million years ago and took its present shape approximately 2.4 million years ago.
History of the Amazon’s flow. Diagram courtesy of the University of North Carolina
The results are consistent with other research which estimated the origin of an eastward-flowing Amazon river at 10 million years. A leading theory holds that the Amazon once flowed west, perhaps as part of a proto-Congo river system, from the interior of present day Africa when the continents were joined as part of Gondwanaland. Fifteen million years ago, the Andes were formed by the collision of the South American plate with the Nazca plate. The rise of the Andes and the linkage of the Brazilian and Guyana bedrock shields, blocked the river and caused the Amazon to become a vast inland sea. Gradually this inland sea became a massive swampy, freshwater lake and the marine inhabitants adapted to life in freshwater. For example, over 20 species of stingray, most closely related to those found in the Pacific Ocean, can be found today in the freshwaters of the Amazon.
Ten to eleven million years ago, waters worked through the sandstone to the west and the Amazon began to flow eastward, leading to the emergence of the Amazon rainforest. During Ices Age, sea levels dropped and the great Amazon lake rapidly drained and became a river, which would eventually become the world’s largest, draining the most extensive expanse of rainforest on the planet.
J. Figueiredo, C. Hoorn, P. van der Ven and E. Soares. Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin. Geology, 37, 619–622.