Mayans were mighty civilization — until they withered in severe drought

Lake study helps answer questions about empire’s fall

The sediment under a lake in Mexico contains some of the long-sought answers to the mystery of the Mayan demise.

Ancient Mayans, primarily concentrated in what is now the Yucatan Peninsula, were among the most advanced civilizations of their time. Mayans were some of the first to build cities. They used astronomy to advance agricultural production, and they created calendars and used advanced mathematics. But despite all of their progress, the Mayan empire, built over thousands of years, may have crumbled in just a few hundred.

Scientists have several theories about why the collapse happened, including deforestation, overpopulation and drought. New research, published in Science, focuses on the drought and suggests, for the first time, how extreme it actually was.

While analyzing sediment under Lake Chichancanab on the Yucatan Peninsula, scientists found a 50 percent decrease in annual precipitation over more than 100 years, from 800 to 1,000 A.D. At times, the study shows, the decrease was as much as 70 percent. While the drought was previously known, this study is the first to quantify the rainfall, relative humidity and evaporation at that time.

It’s also the first to combine multiple elemental analyses and modeling to determine the climate record during the Mayan civilization demise.

Climate scientists commonly use sediment cores to determine the conditions of the past, like geological time capsules. Each layer of sediment buried deep underground contains evidence of rainfall, temperature and even air pollution. Via chemical processes and interactions, the climate conditions are “recorded” in the surface soil at the time, and eventually buried. Scientists can bore a deep core of dirt, and analyze it layer by layer, year by year to reconstruct a timeline.

For this study, scientists examined the layers of mud and clay in the cores from under Lake Chichancanab.

The chemical composition of the fossil water indicated periods of drought in the Mayan timeline, and revealed how long and intense this particular drought was.

Many theories about the drought triggers exist, but there is no smoking gun some 1,000 years later. The drought coincides with the beginning of the Medieval Warm Period, thought to have been caused by a decrease in volcanic ash in the atmosphere and an increase in solar activity. Previous studies have shown that the Mayans’ deforestation may have also contributed. Deforestation tends to decrease the amount of moisture and destabilize the soil.

Additional theories for the cause of the drought include changes to the atmospheric circulation and decline in tropical cyclone frequency, Evans said.