1200 years ago, the Mayan civilization thrived in what are now southern Mexico, Belize and Guatemala. The Mayans were brilliant astronomers and mathematicians, and their society was very stable and established. However, at some point during the 9th century, their civilization suffered a sudden and devastating collapse. Archaeologists have struggled to find an explanation for the Mayans’ fate, but recent studies suggest that a massive drought was responsible. Analysis of mud samples from the bottom of Lake Chichancanab in the Yucatan area of Mexico has found that the region’s climate in the 9th century was the driest that it had been for 7000 years.
The Maya civilisation, which dominated southern Mexico for hundreds of years, appears to have been brought to its knees at least in part by a series of severe, decades-long droughts, scientists say. Conditions were so bad, says Nicholas Evans, a geochemist at the University of Cambridge, UK, that rainfall decreased by 50% on average. During the worst periods, he says, it decreased by up to 70%. The drought was further exacerbated by a 2-to-7% drop in relative humidity, his team found.
The climate shift coincided with an era called the Terminal Classic Period, between 800 and 1000 CE, when the Maya civilisation was in decline and permanently abandoned many of its cities. The idea that drought may have contributed to this collapse isn’t new. “[It] has been debated for at least 100 years,” says Christopher Baisan, a dendrochronologist, or tree-ring scientist, at the US University of Arizona’s Laboratory of Tree-Ring Research, who was not involved in the new study.
But just how severely the climate had changed was not clear. All that was really known was that it was drier than at the height of Maya influence. Evans’ team took core samples of sediments in a lake in the central Yucatan peninsula. “These sediments contain muds,” Evans says, “but importantly, they also contain a mineral known as gypsum.”
Gypsum is a crystal that precipitates out of water when the mineral content grows too large — something that can occur during a drought. It is predominately composed of calcium and sulfate, but it also includes trapped water molecules.
By examining hydrogen and oxygen isotopes in these molecules and comparing them to water in lake today, Evans says, scientists can chart changes in the lake. From these, he says, it’s possible to deduce variations in rainfall patterns.
The result isn’t perfect. To begin with, gypsum only forms during periods of drought, when minerals become concentrated enough to precipitate to the bottom. Also, the isotope levels of the trapped water reflect multi-year averages of climate conditions in and around the lake, not an instantaneous measure.
Picture Credit : Google