Despite years of work, modern scientists still don’t really know much about the people that populated that Amazonian basin prior to the arrival of European explorers. The dense jungle growth has made it difficult to study the area, and the preponderance of poor soils suggests that the area could not have supported large groups of people anyway—the soil would not support the farming necessary to support them. In more recent times, some evidence (ancient roads and earthworks) has been uncovered that indicates that large settlements of people may indeed have indeed populated the area, which would have been made possible by a soil enrichment technique known as terra preta (adding nutrients that resulted in fertile “black earth” that can still be seen today.). Because very few terra preta sites have been found, researchers aren’t sure if they are few and far between, or if there are more simply hidden in the jungle.
Read more at: Phys.org