HISTORIC STATE OF THE AMAZON

The Amazon tropical rainforest began forming in its current location during the Paleozoic era, but it was not until the Cenozoic period, when it began its transformation into what its become today. (Amazon-Rainforest.org) About fifteen million years ago, the South American plate collided with the Nazca plate (southern Peru region), which caused the formation of the Andes mountains. The Andes blocked water paths, turning the Amazon into a large inland sea. Gradually, this sea became a large swampy lake, to which its underwater species adapted to. (Rainforests.Mongabay.com) To this day, similar species are found in the Pacific Ocean. Five million years later, water worked its way through sandstone and flowed eastward toward the Atlantic Ocean. During the Ice Age, sea levels dropped and the lake drained forming a river, known today as the Amazon River. (Rainforests.Mongabay.com) A geological change in the Andes mountains caused water to flow in the west direction, as it does to this day. Three million years later, water levels dropped enough to expose land in the rainforest and attract mammal species. (Rainforests.Mongabay.com) These changes are the reasons for why the rainforest appears the way it currently does.

Sources: amazon-rainforest.org
http://rainforests.mongabay.com/amazon/