The amazon rainforest was not originally a large rainforest. The ground was essentially terraformed, made fertile and trees planted by the ancient amazonians over thousands of years
The BBC’s Unnatural Histories presented evidence that the Amazon rainforest, rather than being a pristine wilderness, has been shaped by man for at least 11,000 years through practices such as forest gardening and terra preta.[20] Terra preta is found over large areas in the Amazon forest; and is now widely accepted as a product of indigenous soil management. The development of this fertile soil allowed agriculture and silviculture in the previously hostile environment; meaning that large portions of the Amazon rainforest are probably the result of centuries of human management, rather than naturally occurring as has previously been supposed.
The amazon rainforest was not originally a large rainforest. The ground was essentially terraformed, made fertile and trees planted by the ancient amazonians over thousands of years
Source: BBC unnatural histories, for over 11000 years the ground was terraformed with “terra preta” and forest was planted and converted
https://en.wikipedia.org/wiki/Amazon_rainforest#History