How Ancient Amazonians Locked Away Thousands of Tons of Carbon in "Dark Earth"

A new study reveals how, by cultivating fertile soil for farming, ancient Amazonians locked away thousands of tons of carbon that have stayed in the ground for centuries.

While the Amazon rainforest is rich in plant life, its soils are poorly suited to growing crops. In a few places, however, archaeologists have uncovered patches of black, fertile soil where ancient humans settled. Until now, it was unclear what role humans played in cultivating this “dark earth.”

For the new study, scientists studied the modern-day farming practices of Indigenous Kuikuro people in the southeastern Amazon, watching as they gathered piles of food scraps, allowed them decompose, and used them to enrich the soil. In some areas, farmers also spread ash or charcoal on the ground.

Scientists saw that the black soil in contemporary villages was strikingly similar to the dark earth found in ancient settlements. It was comprised of the same elements and distributed in the same pattern about the village. Their findings, published in the journal Science Advances, show that ancient people purposefully cultivated dark earth.

What’s more, by burying food scraps, charcoal, and ash, ancient people permanently sequestered huge sums of carbon, as much as 4,500 tons in one village, scientists estimate.

“The ancient Amazonians put a lot of carbon in the soil, and a lot of that is still there today,” said study coauthor Samuel Goldberg, who was a graduate student at MIT when he undertook the research. “Maybe we could adapt some of their Indigenous strategies on a larger scale, to lock up carbon in soil, in ways that we now know would stay there for a long time.”


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