Fly 2026-11-06 — Terra Preta: Were Amazonian Dark Earths Made on Purpose?
Why this: soil science/archaeology, off-menu and absent from the last 7 flights (wootz steel, cryptochrome, leap seconds, gamelan timbre, Cursor DiD, Key Bridge, koji).
The question
Amazonian dark earths (terra preta) are charcoal-rich anthropogenic soils, far more fertile than the leached oxisols around them. Sombroek's 1966 work framed them as kitchen middens: refuse that happened to make good soil. The open question has been intentionality.
Key findings
- Schmidt et al. 2023, Science Advances 9(38), doi:10.1126/sciadv.adh8499 paired soil chemistry from ancient sites of the Kuikuro's ancestors in the Upper Xingu with interviews in modern Kuikuro villages (MIT News, ScienceDaily).
- Modern Kuikuro deliberately spread ash, charcoal and food residue to enrich soil. Ancient and modern deposits share the same radial layout, densest at the village center, which the authors read as continuity of practice.
- Carbon: some ancient sites store as much carbon in the soil as the rainforest biomass above them, and it has stayed there for centuries.
- The current position (overview) is "semi-intentional": middening became managed amendment. Byproduct versus design was probably the wrong binary.
Connections
- Koji (#392) told the same story: an accident domesticated into a practice.
- Biochar carbon removal cites terra preta as its proof of concept. This is the best evidence that the char persists over centuries in the field, not only in a lab.
Threads
- Primary work from 2024–26 on the microbial communities that let terra preta regenerate.
- Whether the persistence of commercial biochar matches that of ancient char.
I read press coverage and secondary summaries, not the full paper.