The Amazon is the largest river in the world, gathering water from all around South America and discharging it into the Atlantic Ocean off the coast of Brazil. With an annual discharge of 6,591 cubic kilometers (1,581 cu mi/a), the Amazon supplies the oceans with 20% percent of the total fresh water they receive; it gives as much water as the next seven largest independent rivers in the world combined.
For years, scientists have tried to determine the exact age of the river, and now a new study shows that the Amazon has been around much longer than previously thought.
The Amazon and the forming of its basin have played a crucial part in the creation of the South American landscape. It served as a bridge but also as a border for the migration and evolution of plant life and animal life on the continent for millions of years. That is why it’s important to pinpoint the exact geological era and point of origin of the Amazon river.
The Amazon river and its drainage basin / Image credit
Amazon tributaries near Manaus (Meeting of Waters) / Photo credit
The task of determining the moment when the Amazon was created is a difficult one. Its geological past is hidden beneath layers of sediment, and its marine history is hard to access. The oldest sediments from the Amazon have been deposited deep into the ocean. In their efforts to find the exact age of the river, researchers have speculated that it’s either as young as 2.6 million years or as old as 11 million years.
In a recent research entitled “The Amazon at sea: Onset and stages of the Amazon River from a marine record, with special reference to Neogene plant turnover in the drainage basin”, made by Universidade do Vale do Rio dos Sinos, São Leopoldo, Brazil, a group of scientists have determined that the Amazon is at least 9 million years old. The researchers made a 2.8 miles (4.5 kilometers) deep borehole in the ocean off the shore of Brazil, at the mouth of the river. After they had analyzed the gathered samples, they noticed a change in material (sediment and plan leftovers) that happened between 9.4 million and 9 million years ago.
A satellite image of the Amazon river mouth (north looking south).
The change in the samples shows that before 9.4 million years ago, the discharged materials came from a water source somewhere in the tropical lowlands and after that, the sediment came from the Andes. This indicates that the Amazon started to make its way across the continent sometime around that 9.4 million years mark.
Farid Chemale, a professor of geosciences and geology at the Universidade do Vale do Rio dos Sinos, São Leopoldo, and one of the authors of the study stated the following:
“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. We applied high-resolution analytical techniques not previously performed in the region”.
A map that shows the most distant source of the Amazon
Another thing that the scientists recorded was how the plant life in the basin of the Amazon changed over time. The samples taken at different locations along the river basin showed that the ecosystem here reacted to a global cool-down that happened sometime between 5 million years ago and 12,000 years ago. As a result, grasses began to grow in the whole region. The appearance of grasslands during this geological age in the region around the Amazon is something that researchers didn’t previously know.
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