The Underwater History of the Amazon Rainforest

The great Amazon is the largest rainforest on the planet, extending about 40 percent of the South American continent and including parts of the following different countries: Brazil, Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana, Suriname and French Guiana that's a department of France.

To submerge such a large expanse of rainforest would be a massive undertaking, but a new study by researchers from the Smithsonian Tropical Research Institute (STRI) suggested that that was exactly what happened -- twice. According to a report from Science Magazine, a significant part of the rainforest may have been flooded by the Caribbean Sea twice over 10 million years ago. This spurred the evolution of new species that live in the Amazon. It has resulted in about 10 percent of the planet's species being found in this rainforest.

However, not all scientists agree with the findings. Many are in agreement that the Amazon has been underwater for a time but disagree on the source of the water.

"Pollen records from oil wells in eastern Colombia and outcrops in northwestern Brazil clearly show two short-lived events in which ocean water from the Caribbean flooded what is now the northwest part of the Amazon basin," lead author and STRI scientist Carlos Jaramillo said in a statement. "Geologists disagree about the origins of the sediments in this area, but we provide clear evidence that they are of marine origin, and that the flooding events were fairly brief."

Jaramillo and his colleagues dated the two Amazon rainforest floods at between 18 to 17 million years ago and between 16 to 12 million years ago. The first flood was estimated to have lasted 200,000 years, while the second stretched longer for 400,000 years.

The team studied evidence of over 50,000 individual pollen grains from 900 pollen types from cores. In their analysis, they came across two different layers of marine pollen that's separated by layers of non-marine pollen. There were also fossils of marine animals like a shark tooth and a mantis shrimp.

The study about the underwater history of the Amazon rainforest is published in the journal Science Advances.