dark earth

A soil pit dug into dark earth in the Amazon (Morgan Schmidt photo)
Entrenched rivers in the Amazon Basin
Dark earth: Carbon-rich soils in the Amazon

The size of ancient human populations in the Amazon and the extent of their ecological impacts are hotly debated. Central to this debate is Amazonian dark earth (ADE) – anomalous anthropic soil characterized by darker colour, higher organic carbon content, and higher fertility than typical Amazonian upland soils. Archaeological evidence indicates that dark earth formed in association with human occupation, but it is uncertain what practices created dark earth, what determined its spatial extent, and whether humans created it intentionally, leading some researchers to still question whether humans created it at all. The amount of carbon distributed across dark earth sites is largely unknown, adding uncertainty to the potential climate impacts of soil carbon loss due to land-use change and global warming.

Morgan Schmidt and Sam Goldberg are collaborating with Profs. Heather Lechtman and Dorothy Hosler (MIT Department of Materials Science & Engineering) and a network of collaborators in Brazil to investigate the origins and carbon storage of dark earth. They have discovered similarities between dark earth in ancient and modern contexts, and Morgan has documented contemporary indigenous practices that enrich soil. This comparison suggests that ancient Amazonians managed soil to improve fertility and increase crop productivity. These practices also sequestered and stored carbon in the soil for centuries, and Morgan and Sam have calculated that the organic carbon content of some ancient dark earth sites is comparable to that of the above-ground rainforest biomass. Their results demonstrate the intentional creation of Amazonian dark earth and highlight how indigenous knowledge can provide strategies for sustainable rainforest management.

  • Schmidt, M., S.L. Goldberg, (24 others), and J.T. Perron. Intentional creation of carbon-rich soils in the ancient Amazon. In review.