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The Amazon Basin was formed 500 million years ago when Ancient Gondwanaland was broken up due the tectonic action between the Nazca Plate and the South American Plate. Sediment eroded from Gondwanaland brought by rivers flowing west, and being deposited where the Amazon Basin currently exists. 200 million years ago the convections currents forced the denser Nazca Plate to subduct underneath the lighter South American Plate causing previous sediments to be pushed upwards and form Fold Mountains such as the Andes, which are up to 6000m high. 1 million years ago high rainfall resulted in many rivers, (over 1000 tributaries) which eroded the soft rock of the Andes. The River was forced to change directions and flow into the Atlantic Ocean rather than the Pacific Ocean. This caused the rivers to deposit sediments on the flatter Basin and built up the flood plain. Over time the rivers have built up the basin, making it shallower and flatter. Today there is only a 100m-drop from the edge of the Andes foothills to the Amazon River Mouth.

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12y ago

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