Researchers from MIT, the University of Florida, and Brazil determined that the enigmatic "dark earth" seen in the Amazon was purposefully manufactured by ancient Amazonians to boost soil fertility and support big communities.

Implications for Climate Change Mitigation

This revelation could have a substantial impact on present climate change mitigation efforts.

The Amazon rainforest, noted for its luxuriant foliage, is supported by surprisingly infertile soils. However, archaeologists have discovered pockets of black, productive soil, known as "dark earth," near ancient human settlements.

Until today, it was unclear if this fertile soil was intentionally cultivated or an unintended consequence of these ancient cultures.

Fertile Oases in the Amazon

The research team used soil analysis, ethnographic observations, and interviews with modern Indigenous people to show that ancient Amazonians purposely created dark earth.

Interestingly, dark earth contains massive amounts of stored carbon that have accumulated over hundreds to thousands of years as generations nourished the soil with food scraps, charcoal, and garbage.

This inadvertent carbon sequestration could be used to support modern climate change mitigation efforts. 

The team's results, published in Science Advances, are based on data gathered in the Kuikuro Indigenous Territory in the Upper Xingu River basin in Southeast Amazon.

The researchers observed modern Kuikuro soil management practices, such as the creation of "middens" - piles of waste and food scraps comparable to compost heaps that degrade and mix with the soil to generate black, fertile earth.

The researchers also conducted interviews with villages to document the Kuikuro's beliefs and behaviors around dark earth.

Ancient Wisdom for Modern Agriculture

The people referred to black dirt as "eegepe," and recounted their everyday methods for generating and cultivating the fertile soil to increase its agricultural productivity.

The team's meticulous analysis of soils from both archaeological and modern sites revealed similarities in the spatial structure and composition of dark earth, implying that ancient Amazonians intentionally worked the soil, most likely using practices similar to those used today, to grow enough crops to sustain large communities.