This dark earth is often referred to as terra preta which has been a subject of study for a long time. The debate on whether it was intentionally made vs other

This dark earth is often referred to as terra preta which has been a subject of study for a long time. The debate on whether it was intentionally made vs other explanations has been going on for a while, the posted article adds more to the human-made explanation, more on terra preta here: https://en.wikipedia.org/wiki/Terra_preta https://en.wikipedia.org/wiki/Terra_preta