Age of the Amazon River estimated at 9 million years

LÉO RAMOS CHAVES New dating is based on analyses of sediments from an oil drilling hole at the mouth of the riverLÉO RAMOS CHAVES

The Amazon River is so large and complex that its tributaries are often the subject of debate and redefinition. While there is no doubt that it is the largest freshwater system on Earth, there is a continuing debate as to whether it is longer than the Nile, which is often referred to as the longest river on the planet. The exact age of the Amazon River is another point of contention. A new study by Dutch and Brazilian researchers estimates that the river formed between 9.4 and 9 million years ago, not 3 million years ago as some recent studies have suggested (Global and Planetary Change, March 20). The new dating is based on geochemical and palynological (pollen and plant spores) analyses of sediment collected from an offshore oil drilling hole at the mouth of the Amazon, where the river meets the Atlantic Ocean on the coast of the state of Pará. The borehole reaches a depth of 4.5 kilometers below sea level and is located within the Amazon’s submarine fan, where the sediments transported by the river are deposited. The area is therefore important to accurately determining the evolutionary history of the river, which originates in the Peruvian Andes and crosses the northern region of South America. “We were able to reduce the number of uncertainties regarding when the Amazon was formed,” says geologist Carina Hoorn of the University of Amsterdam, lead author of the paper. A team from the University of Brasília (UNB) coordinated by geologist Farid Chemale Jr. also participated in the research. A previous analysis, performed by Hoorn and other researchers in 2009 using material from the same submarine borehole, estimated the Amazon’s age at 11 million years, an estimate that has now been revised.