DID DROUGHT END MAYAN CIVILIZATION?
Scientists study ancient lake sediment for clues
The sediment under a lake in Mexico contains some of the longsought answers to the mystery of the Mayan demise.
Ancient Mayans, primarily concentrated in what is now the Yucatán 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 extreme 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-per-cent 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 per cent.
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 modelling to determine the climate record during the Mayan civilization’s 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 carefully 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. During dry periods, the lake volume would have shrunk, said Nick Evans, a graduate student studying paleoclimatology at Cambridge University and first author of the study. As the water evaporated, lighter particles would have evaporated first, leaving behind heavier elements.
If the drought was intense and long-lasting, gypsum crystals formed and incorporated existing lake water directly into their structure. The “fossil water” inside the crystals allowed Evans and his coauthors to analyze the properties of the lake water during each period.
“It’s as close as you’ll ever get to sampling water in the past,” Evans said.
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 atmospheric circulation and decline in tropical cyclone frequency, Evans said.
Matthew Lachniet, a professor of geosciences at the University of Nevada Las Vegas, who was not involved in the study, said the quantification of the drought is important because it illustrates the power of natural climate variability alone.
“Humans are affecting climate. We’re making it warmer and it’s projected to become drier in Central America,” Lachniet said. “What we could end up with is double whammy of drought. If you coincide drying from natural causes with drying from human causes then it amplifies the strength of that drought.”
Evans and his team hope their research will help archaeologists understand how the drought may have impacted Mayan agriculture at a critical time in their history.
Currently, vast areas of North America, northern Africa, the Middle East, Southwest Asia and most of Australia are in significant drought, according to the National Oceanic and Atmospheric Administration’s Global Drought Information System. Research suggests that drought may cause war, famine and large human migrations.
“Drought does have the potential to be a driving force for a lot of the issues that can cause civilization stress,” Evans said. He noted, though, that today’s globalized economy and modern technology have the potential to prevent a Mayan-style, world-ending drought.
Probably.