About six years ago, researchers first suggested that a severe drought may have precipitated the mysterious fall of the Mayan Empire. A new study in today's Science finds that this kind of drought may return with a certain regularity because it is a result of a shift in solar intensity.

The sun's intensity actually varies less that one tenth of a percent, but it is enough to create severe droughts in the Yucat¿n Peninsula, formerly the heart of the Mayan Empire. "It looks like changes in the sun's energy output are having a direct effect on the climate of the Yucat¿n and causing the recurrence of drought, which is influencing the Maya evolution," says lead author David Hodell of the University of Florida.

In sediment cores taken from Lake Chichancanab in northern Yucat¿n, the researchers found periodically reoccurring high concentrations of calcium sulfate, which is left behind when greater amounts of water evaporate from the ground during droughts. Based on this pattern, they concluded that the droughts occurred in a 208-year cycle. They further noted that this cycle closely coincided with a known 206-year variation in solar activity.

When the scientists compared the development of Mayan civilization with these cycles, it became evident that the society's development was slowed down every time the droughts occurred. The Maya relied heavily on rainfall and surface water, and both the end of the classical period and the ultimate demise of Mayan civilization coincided with one of these droughts.

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