for National Geographic News
With their awe-inspiring architecture and sophisticated concepts of astronomy and mathematics, the Maya were undoubtedly among the great ancient civilizations of Mesoamerica. At the peak of their glory, around 800 A.D., the Maya ranged from Mexico's Yucatán peninsula to Honduras.
Then, almost in an instant, a society of some 15 million people imploded, leaving deserted cities, trade routes, and immense pyramids in ruins. The sudden demise is one of the greatest archeological mysteries of our time. What caused the collapse of the great Maya civilization?
The answer, say researchers, is climate change. According to a new study published in the current issue of Science, a long period of dry climate, punctuated by three intense droughts, led to the end of the Maya society. "Climate change is to blame for one of the most catastrophic collapses in human history," said Gerald Haug, a professor of geology at the University of Potsdam, Germany, and one of the study's authors.
Identifying the Culprit
The drought hypothesis is not new. Sediments taken by scientists in 2001 from a lake on the Yucatan peninsula showed that a series of extended droughts coincided with major cultural upheavals among the Maya people.
But the study of that lake also found man-made effects, such as deforestation and soil erosion, and therefore didn't reflect a "pure climate signal," according to Haug. For the new study, the scientists instead analyzed sediment core from the Cariaco Basin off northern Venezuela, where the record is cleaner.
Identifying annual titanium levels, which reflect the amount of rainfall each year, the Swiss and U.S. researchers found that the pristine sediment layers in the basin formed distinct bands that correspond to dry and wet seasons. According to the scientists, there were three large droughts occurring between 810 and 910 A.D., each lasting less than a decade.
The timing of the droughts matched periodic downturns in the Maya culture, as demonstrated by abandonment of cities or diminished stone carving and building activity.
Experts say the Maya were particularly susceptible to long droughts because about 95 percent of their population centers depended solely on lakes, ponds, and rivers containing on average an 18-month supply of water for drinking and agriculture.
Reading the Sun
The Maya were skilled astronomers who constantly followed the movements of the sun and the moon. They predicted eclipses, explained the movements of planets, and devised a sophisticated calendar of the solar year.
Scientists have found that the recurrence of the drought was remarkably cyclical, occurring every 208 years. That interval is almost identical to a known cycle in which the sun is at its most intense every 206 years. Nothing suggests the Maya knew anything about the sun's change in intensity.
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