well I suppose it depends what you define as the starting point but it's generally recognized it began in the Eocene epoch (55.8 million years to 33.9 million y

well I suppose it depends what you define as the starting point but it's generally recognized it began in the Eocene epoch (55.8 million years to 33.9 million years ago) Not sure how that's relevant to the sentence you quoted though. The Amazon rainforest has been largely savanna type ecosystems at various points in its history. Including quite recently (like 12kya)