The sun sets behind the Kukulkan pyramid in Chichen Itza, Mexico, where the last stone monuments were carved prior to the collapse of the Maya civilization.
Archaeologists have long suspected that climate change may have caused
droughts that brought the agriculture-based Maya civilization to its knees. A new study published in Science
last week bolsters this theory with new physical evidence, showing that ancient droughts correspond with political upheaval as recorded in stone carvings. Scientists generally figure out what long-ago climates looked like by measuring oxygen isotopes
in sediment samples. These isotopes are variations on the oxygen atom that have eight, nine, or ten neutrons, depending on the amount of water present when the sediment was deposited. A sediment layer's ratio of heavy versus light oxygen isotopes can tell scientists when the layer was formed and what the climate was like at that time. Researchers in past studies have relied on sediment cores from lakes
, but the researchers in this study used a stalagmite from a cave near the ancient Maya city of Uxbenká, in present-day Belize. Protected by the cave, the stalagmite's layers were better preserved than those from the bottom of a lake or ocean. Plus, the data derived from these layers were much more detailed. The scientists were able to see what the climate was like in Mesoamerica over the past 2,000 years, and zoom in to intervals as short as 6 months. The scientists compared their new and improved climate timeline with historical records the Maya carved into nearby stone monuments and found some interesting overlap. A period of unusually wet conditions in the mid-fifth century coincides with carvings that describe a major population boom and the expansion of political centers. A drying trend in the later half of that century corresponds to records of political disintegration and warfare. For 80 years after the dry spell, climate records indicate extreme drought conditions, and the concurrent lack of stone monuments suggests that Mayan leaders were no longer commissioning them to be carved. With this new physical evidence of a climate change-related collapse, the researchers have reinforced theories that the once-great Mayan civilization dried up sometime between 1020 and 1100 A.D.
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