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NatureScience

The Amazon Changed from Wetland to River

Much of our planet is not what it once used to be: mountains have risen and collapsed; continents broken apart and crashed into one another; and according to a report to be published in the journal Nature Geoscience, the world’s largest river – the Amazon – started life out as a massive swath of wetland.

According to PhD candidate Grace Shephard and Professor Dietmar Müller from The University of Sydney, Australia, and a team of international colleagues, the Amazon used to be a huge area of wetland connected to the Caribbean until 14 million years ago.

The uplift of the Andes mountain range was originally assumed to be the culprit for the formation of the Amazon, blocking the westward flow of water; however Shephard and her colleagues believe that progressive continental tilting is the real force behind the formation of the planet’s largest river.

“We had a hunch that the ultimate forces leading to this fundamental shift in continental topography had something to do with the westward motion of South America over dense, sinking mantle rocks while the Atlantic Ocean opened up,” she said.

“We used a high-performance computer model to simulate the workings of this giant tectonic conveyor belt, with South America progressively being translated westward over an ancient subduction zone along the continent’s west coast.”

Professor Müller said here, along the edge of the Pacific, ocean crust had plunged into the sticky rocks of the Earth’s mantle for eons.

“This process created a massive crustal graveyard deep inside the Earth, where huge masses of old, cold tectonic slabs are sinking, drawing the surface down,” he said.

“As South America made its way westward over this ‘slab burial ground’, the continent’s northeast was progressively drawn down by several hundred meters, creating something akin to the world’s largest water slide.”

Source: The University of Sydney




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