Stalagmites in a Yucatan cave reveal why the Mayan civilization collapsed.

Archaeologists have long been trying to determine what exactly caused the collapse of the Mayan civilization . The earliest Mayan settlements are about 3,000 years old, dating back to the first millennium BC, but the culture reached its peak around the year 600. Thousands of ancient Mayan cities have been discovered, mostly located in the southern Yucatán Peninsula of Mexico, Belize, and Guatemala, where they left behind traces of their significant advances in fields such as writing, art, architecture, mythology, mathematics, and astronomy.

But around 850, after two millennia of prosperity and dominance, the Maya began abandoning their great cities en masse . In less than two centuries, that civilization was reduced to a shadow of its former glory. What caused the collapse of Mayan culture ?

A team of researchers has now provided new evidence about the reasons that may have led to this inexplicable debacle. According to a statement issued by the University of Cambridge, the scientists analyzed oxygen isotopes from stalagmites found in the Tzabnah Caves in Yucatán, Mexico, which provide valuable information about the amount of rainfall in the area from 871 BC to 1021, during both dry and wet seasons. The information gathered reveals that there were eight droughts during that time period, all of which lasted at least three years.

Researchers have even found evidence of a particularly catastrophic drought that lasted 13 consecutive years. And although the Maya had a sophisticated system of channeling and harnessing water, such a prolonged drought undoubtedly had a profound impact on their political and social structures.

"There have been multiple theories about the causes of the collapse of that civilization, such as changing trade routes , warfare , or severe drought, based on the archaeological remains left behind by the Maya," notes Cambridge University researcher Daniel H. James . "But in recent decades, by combining archaeological data with quantifiable climate evidence, we have begun to understand what happened to the Maya and why."

It was only in the 1990s that researchers began combining climate records with information left behind by the Maya themselves , such as key dates (or lack thereof) on monuments, to try to show that a series of severe droughts contributed to the collapse of that civilization. Now Daniel H. James and other researchers from Great Britain, the United States, and Mexico have used the chemical fingerprints contained in stalagmites from a cave in northern Yucatán to analyze these droughts more precisely. This is the first time it has been possible to individually isolate rainfall conditions for the wet and dry seasons during the period of decline that culminated in the collapse of the Maya culture. The results of this research have just been published in Science Advances .

Stalagmites, as we know, form when water drips from the ceiling of a cave, and the minerals it contains accumulate in large deposits on the floor. By dating and analyzing the oxygen isotope layers within the stalagmite, researchers have gained very detailed information about the climate during the Maya era, and specifically about the so-called Terminal Classic Maya Period, which spanned approximately 800/830 AD to 950/1000 AD and was characterized by the decline and abandonment of many important cities.

During periods of prolonged and severe drought, date inscription at sites such as Chichén Itzá ceased altogether.

Previous research on stalagmites had already determined average annual rainfall during the Terminal Classic Period, but the University of Cambridge team has now gone further and managed to isolate individual pieces of information about the wet and dry seasons. “Knowing the average annual rainfall doesn't reveal as much as knowing what each wet season was like,” says Daniel H. James. “Being able to isolate the wet season allows us to accurately track the duration of the wet-season drought, which is what determines the success or failure of crops.”

According to the information contained in the stalagmites, between 871 and 1021 AD there were eight wet-season droughts, each lasting at least three years, although the longest drought lasted 13 years. The climatic information contained in the stalagmites at the Caves of Tzabnah matches the dates recorded by the Maya on their monuments . During periods of prolonged and severe drought, date inscription at sites like Chichén Itzá ceased altogether. “That doesn’t necessarily mean that the Maya abandoned Chichén Itzá during these periods of severe drought, but they likely had more immediate concerns than monument building, such as the success of the crops on which they depended,” James notes.