Fall Of The Mayans

There's a spine-chilling moment in the film "Titanic," after the ship has struck an iceberg, when an engineer declares disaster to be "a mathematical certainty." Gerald Haug had a similar epiphany of doom one evening at his Zurich home last year. He had put his 3-year-old son to bed at 8 o'clock and then sat down to read "The Great Maya Droughts." The book boldly addressed the biggest mystery in New World archeology--why the magnificent Mayan civilization, which had flourished for centuries and once had a population in the millions, disappeared so suddenly in the 9th century. The reason, argued author Richardson Gill, was three catastrophic droughts that struck with the consistency of a metronome: in A.D. 810, 860 and 910. Mainstream archeology wasn't having any of Gill's theory, but Haug, a paleoclimatologist whose lab had been taking climate measurements of the same period, found it riveting. At about 2 in the morning, he put down the book and checked the latest results from his lab. The data gave him a jolt: they showed a century ravaged by three successive droughts -- beginning in 810, 860 and 910. "I was bouncing around the living room," says Haug.

Haug's measurements of ancient climate variations in the Cariaco Basin off the coast of Venezuela--hundreds of miles from the Mayan sites in Mexico, Guatemala and Belize, but affected by the same weather patterns--confirmed the existence of Gill's droughts. Haug's research, published last Friday in the U.S. journal Science, has provided the most conclusive evidence to date that a series of droughts in 9th-century Central America was an important cause--perhaps the main cause--of the collapse of Mayan civilization. The data downplays competing theories that emphasize a complicated interplay of ecology, disease, overpopulation and even class warfare. "Careers were made by coming up with these very complex theories," says Gill.

For the past century archeologists relied on paleontology-centered methods of inquiry that put a premium on digging for artifacts and bones for evidence. Research yielded excellent portraits of Mayan social and economic interactions, but it never answered the Big Question. And it yielded no evidence that climate played much of a role--a big reason why archeologists discounted it. In the 1990s, a chorus of geologists, paleoclimatologists and other scientists began to reconsider. The most strident and unorthodox new voice was Gill, a former banker and freelance archeologist.

As a child growing up in Texas, Gill had seen severe drought. When the Texas economy tanked in the 1980s, he started investigating a hunch that drought killed off the Mayans. Most university archeologists told him respectfully--but plainly--that they didn't think he was looking in the right place. The first supporting evidence came in 1995, from geologist David Hodell at the University of Florida. He and his team examined layers of sediment underneath Mexico's Lake Chichancanab, which showed the first evidence of a catastrophic drought--the worst in 7,000 years--around the turn of the 10th century. That was enough for Gill. In his book, published in 2000, he proposed dates for three severe droughts. Most archeologists dismissed both the book and Hodell's evidence--which relied on imprecise radiocarbon dating.

Haug, in 1996, was standing on the deck of a ship off the coast of Venezuela when workers hauled up a tube of sediment 170 meters long--encompassing 500,000 years of climate history. Six centimeters wide and greenish-brown, the core sample is made up of millions of tiny layers, a year to each half millimeter. As Venezuela's rivers empty into the Cariaco Basin, they leave a chemical signature in the sediment that reveals how much rain fell that year. In 2001, Haug used the core-sample data to narrow the timing of the droughts to within four to five years, which left many archeologists unmoved. Haug then teamed up with chemist Detlef Gunther--who, like Haug, worked at the Swiss Federal Institute of Technology. Using X-rays, Gunther was able to focus the precision to within two months. "It's a superb piece of work and I want to know when these guys can come to the Near East with me," says Yale archeologist Harvey Weiss, who has studied the effects of climate on the Mesopotamians. Haug's latest results show enormous, abrupt swings of climate over the last century of Mayan society.

It will take time for scientists to integrate the great droughts into their story of the Mayan's "demographic disaster." They've already chronicled power struggles, crop failures and political crises. Three droughts must have put great pressure on Mayan society. Some Mayan archeologists, though, aren't convinced that Haug makes an ironclad case. "This is not good science," says UT Austin's Karl Butzer. Others say Mayan specialists are just guarding their turf. "The significance of Hodell's research was clear to all but the Mayan archeologists," says Weiss. "But those Mayan archeologists who previously went ballistic with Hodell's data will be hospitalized by this article."

Scientists will convene in August in Guatemala to work through the new data. They'll be a few hours' drive from a spot where, toward the end, disillusioned Mayans are thought to have faced down their elites--and beheaded them. This year's meeting will be more civil, but no less confrontational.