Maya and Aztec

American Geophysical Union, February 3, 2011. New detailed data on the variability in precipitation in ancient Mexico, covering the 1238-year period, will help scientists understand the role played by the drought in the formation and incidence of pre-Columbian civilizations. Studies indicate that the drought could play a key role in the fate of the main crops of ancient Mexico and Central America (Mesoamerica).

The new study was the most inclusive and most accurate of these ongoing studies in Mesoamerica. It revealed four mega drought and dates when they happened.

Thus, one of these droughts, which, as previously thought, covered the territory of south-western United States, also applies to the territory of Central Mexico, and lasted from 1149 to 1167 AD. Thus, according to the head of a new study, David Stahle, paleoclimatologist at the University of Arkansas at Fayetteville, this drought could drastically reduce the harvest of maize, which probably was a fatal blow to the declining Toltec culture. He and his colleagues will publish the results of their research in «Geophysical Research Letters», a journal of the American Geophysical Union.

New data from the study were also more accurately recorded, and the other 2 long period of severe drought revealed to scientists. These data will help to look more precisely at the success of the formation of the Aztec empire and the spread of the exotic diseases brought by Spanish conquistadors.

This study also became the first independent confirmation of the existence of a drought late classical period – mega drought with which some anthropologists have linked the collapse of Mayan civilization. Previously, the prolonged dry period has been known through the analysis of sediments at the bottom of various lakes of Mexico and Caribbean coasts. However, the team got a more precise dating (897-922 AD) – also an area of drought was much wider than previously thought. Thus, the drought has also affected the highlands of central Mexico, where other civilizations have evolved in classical period.

“Certainly these cultural changes were very complicated — probably not one single explanation can account for the collapse of the Mayan civilization,” Stahle says. “[But] our study will allow other scientists to more thoroughly investigate and understand the impact of these droughts.”

In their study’s authors used data from 74 samples extracted from the core of 30 trees, millennium-old Montezuma baldcypress trees (Taxodium mucronatum). Samples were taken from trees growing in the canyon Amealco (Queretaro), located only 90 km from Tenochtitlan, the capital of the Aztec Empire, and 60 km northeast from Tula, the Toltec state’s main city. Stahle said that these trees, the relatives of the North American redwoods, the only Central American plants, which often live up to a thousand or more years.

“This is the national tree of Mexico, and it tells such an interesting story of the decline of the Mexican empires”, says Stahle, adding that previous tree chronologies for Mexico were only three to four centuries long. “This is the first one that goes back into pre-Hispanic times,”

Researchers have identified a year of each of the annual rings of a tree and analyzed them, which made it possible to obtain accurate data on soil moisture, in which there were trees and, accordingly, an abundance of rainfall in the year. “The beauty of tree rings is that they’re annual: you get an estimate for wetness for every single year — you don’t get it from other archives, not as precisely,” Stahle says.

“This research… highlights the role fine-grained climate data can play in helping us understand the trajectories of past human societies,” says David Anderson, an archaeologist at the University of Tennessee, Knoxville who was not involved in the new study. “This study will prompt a great deal of follow-up research by archaeologists and paleoclimatologists alike, and offers lessons for our own civilization — specifically how vulnerable complex societies may be to drought-induced crop failures.”

Source –  AGU