more than one eye in the room had a distinctly evangelical gleam. The soil scientists, archaeologists, geographers, agronomists, and anthropologists who study terra preta now agree that the Amazon’s dark earths, terra preta do índio , were made by the river basin’s original human residents, who were much more numerous than formerly supposed. The darkest patches correspond to the middens of settlements and are cluttered with crescents of broken pottery. The larger patches were once agricultural areas that the farmers enriched with charred trash of all sorts. Some soils are thought to be 7,000 years old. Compared with the surrounding soil, terra preta can contain three times as much phosphorus and nitrogen. And as its colour indicates, it contains far more carbon. In samples taken in Brazil by William Woods, an expert in abandoned settlements at the University of Kansas in Lawrence, the terra preta was up to 9% carbon, compared with 0.5% for plain soil from places nearby 1 . From Smith’s time onwards, the sparse scholarly
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