The Amazon River Basin is a complicated mosaic of ecosystems where you can find about a third of all terrestrial plant, animal and insect species known to humans. In present times this enormous area is a home to millions of people with scientific evidence showing that it has been inhabited by humans for thousands of years earlier. The Amazon River is the lifeblood of these ecosystems and the main reason why this region has been inhabited by humans since time immemorial.
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 /Author: Kmusser – CC BY-SA 3.0
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.
Amazon tributaries near Manaus (Meeting of Waters) / Author: Neil Palmer/CIAT – CC BY-SA 2.0
In a recent research project, published earlier this year under the title 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, a group of scientists have determined that the Amazon is at least 9 million years old. Researchers from the University of Amsterdam, Universidad Distrital Francisco José de Caldas in Colombia, the Universidade de Brasília, and the Smithsonian Tropical Research Institute, Panama, examined sedimentary deposits from a 2.8 miles (4.5 kilometers) deep borehole in the ocean off the shore of Brazil, at the mouth of the river. Geochemical analysis of the samples showed a change in material in the layers that were laid down 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.
According to an article published on the official website of the University of Amsterdam, Farid Chemale, a professor of geosciences and geology at the Universidade do Vale do Rio dos Sinos, Brazil, and one of the authors of the study, stated that:
“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 studied was how the plant life in the basin of the Amazon changed over time. Evidence in the form of pollen and other airborne particles that would have fallen on the flowing water and then settled into the river sediment was analyzed, a discipline known as palynology. The samples indicate that the ecosystem along the river basin 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.
