Magazine article Science News

Not So Clear-Cut: Soil Erosion May Not Have Led to Mayan Downfall

Magazine article Science News

Not So Clear-Cut: Soil Erosion May Not Have Led to Mayan Downfall

Article excerpt

Hand-planted maize, beans, and squash sustained the Mayans for millennia, until their culture collapsed about 1,100 years ago. Some researchers have suggested that the Mayans' very success in turning forests into farmland led to soil erosion that made fanning increasingly difficult and eventually caused their downfall. But a new study of ancient lake sediments has revealed that most erosion happened well before the culture collapsed and likely played only a small role in disrupting the civilization.

"When you clear a forest, you open up the soil and expose it to rainfall and weathering," says Flavio S. Anselmetti, now of the Swiss Federal Institute of Aquatic Science and Technology in Duebendorf. In the tropical lowlands, he explains, clay soils can drift substantially, but only after forest clearing.

To assess soil erosion during the Mayan era, Anselmetti's team measured how much clay had washed into Guatemala's Lake Salpeten. The layer of clay, 7 meters thick at some spots, contrasts sharply with nutrient-rich organic material below and above it, which was deposited before and after the Mayan period.

By analyzing the ages of different layers within the clay, the researchers determined that most of it accumulated 2,700 to 4,000 years ago, early in the Mayan era. Erosion must have begun as soon as the Mayans started clearing land for agriculture, say Anselmetti and his colleagues in the October Geology.

Vernon L. …

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