No. 118: Jul-Aug 1998
Most of the lush jungles of tropical South America grow on a very thin layer of soil that is continuously regenerated by decaying vegetation. Deforest the jungle and the agricultural potential is about that of a your nearest Interstate highway. But the so-called "terras pretas" are curious exceptions. Spotted along Brazil's Aripuana River are small areas of deep, black earth that are from 7 to 17 feet deep. These are the "terras pretas" or "black earths." Scientists believe that these fabulously productive "islands" in the sea of otherwise poor soil were developed by native peoples about 10,000 years ago. No one knows how these ancient farmers made the terras pretas. The slash-and-burn farming of the present inhabitants is primitive in comparison.
(Anonymous; "Fertile Soil of Ancient Tribes Poses Puzzle," Columbus Dispatch, January 11, 1998. (Cr. J. Fry via COUD-I)