Centuries-old European explorers' tales of lost cities in the Amazon have long been dismissed by scholars, in part because the region is too infertile to feed a sprawling civilization.
But new discoveries support the idea of an ancient Amazonian urban network—and ingeniously engineered soil may have made it all possible.
(See Ancient Amazon Cities Found; Were Vast Urban Network [August 28, 2008].)
Now scientists are trying to recreate the recipe for the apparently human-made supersoil, which still covers up to 10 percent of the Amazon Basin. Key ingredients included of dirt, charcoal, pottery, human excrement and other waste.
If recreated, the engineered soil could feed the hungry and may even help fight global warming, experts suggest.
(Interactive map: "The Embattled Amazon.")
Before 1492
Scientists have long thought the river basin's tropical soils were too acidic to grow anything but the hardiest varieties of manioc, a potatolike staple.
But over the past several decades, researchers have discovered tracts of productive terra preta—"dark earth." The human-made soil's chocolaty color contrasts sharply with the region's natural yellowish soils.
Video Clip From Lost Cities of the Amazon Documentary
Research in the late 1980s was the first to show that charcoal made from slow burns of trees and woody waste is the key ingredient of terra preta.
With the increased level of agriculture made possible by terra preta, ancient Amazonians would have been able to live in one place for long periods of time, said geographer and anthropologist William Woods of the University of Kansas.
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