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 or oceans, but the researchers in this study used a stalagmite from a cave near the ancient Maya city of Uxbenká, in present-day Belize.