National Geographic : 2008 Sep
Scarce Fertility Today more than six billion people rely on food grown on just 11 percent of the global land surface. Even less ground-a scant 3 percent of the Earth's surface-offers inherently fertile soil (dark and medium green areas, below). Soil degradation can transform productive zones into wastelands with tragic speed. "The history of every nation," U.S . President Franklin Roosevelt said, "is eventually written in the way in which it cares for its soil." Terra Preta do Indio-Black Indian Earth Between 2,500 and 500 years ago in the Amazon Basin, people created deep layers of carbon-enriched earth, enhancing the fertility of poor, shallow soils. SURROUNDING TERRA (NORMAL) PRETA SOILS Amazon Soil Layers Organic Topsoil up to 8 inches deep Subsoil _ -Topsoil up to 6.5 feet deep 30-150 150-500 Terra preta sites Archaeologists have identified pockets of rich topsoil that built up as charcoal, along with food refuse and other wastes, including broken pottery, was mixed into stingy soil: The deposits range in size from two or three acres (typical) to as much as 30 to 40 acre 150° 120° 90° 92 NATIONAL GEOGRAPHIC * SEPTEMBER 2008 CANADA NORTH Palouse Hills (WA)- 'Coon Creek Watershed (WI) ATLANTIC OCEAN PACIFIC OCEAN HAITI Weathered rock Rock River BRAZIL H. .*^ CARBON CONTENT Tons per hectare to a depth of one meter 60°W Ki*~ I $r~ - "";r: ~~.