Why the Mayan society, which prospered in the eighth and ninth centuries in Central America, collapsed remains a mystery. Numerous theories, from overpopulation and class warfare to climate change and environmental stresses, have been put forward over the years to explain the downfall. Now the most detailed sediment analysis yet, published in the current issue of the journal Science, further implicates climatic variation. It suggests that a prolonged dry spell, punctuated by three more severe droughts, could have been chiefly to blame for the civilization's demise.

Gerald H. Haug, now at Potsdam's Geoscience Center, and his colleagues studied a sediment core collected from the Cariaco Basin, located off the coast of northern Venezuela. By analyzing the levels of titanium, which is indicative of the amount of rainfall, the scientists determined that the area around the Yucatán peninsula (now part of Mexico) suffered three periods of very low rainfall around A.D. 810, 860 and 910. The droughts were relatively short-lived, lasting between three and nine years, the authors report. They note that these findings agree with archaeological evidence that suggests that Mayan society collapsed in three phases over the same time period.

The latest results will not be the last word on the Mayan collapse, however. Indeed, the authors note that "no one archaeological model is likely to capture completely a phenomenon as complex as the Mayan decline." No doubt scientists will be uncovering the secrets of this sophisticated society for years to come.