The Amazon River in South America is the largest river by discharge volume of water in the world, and the disputed longest river in the world.

The Amazon River originated as a transcontinental river in the Miocene epoch between 11.8 million and 11.3 million years ago and took its present shape approximately 2.4 million years ago in the Early Pleistocene.

The proto-Amazon during the Cretaceous flowed west, as part of a proto-Amazon-Congo river system, from the interior of present-day Africa when the continents were connected, forming western Gondwana. 80 million years ago, the two continents split. Fifteen million years ago, the main tectonic uplift phase of the Andean chain started. This tectonic movement is caused by the subduction of the Nazca Plate underneath the South American Plate. The rise of the Andes and the linkage of the Brazilian and Guyana bedrock shields, blocked the river and caused the Amazon Basin 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.

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