Mayan civilization reached its peak on the Yucatan Peninsula in 250 BC. Its large, intellectually developed cities filled with complex architecture and art were abandoned nearly a thousand years ago and the cities’ inhabitants disappeared almost entirely. Until recently, a severe drought was thought to have caused the collapse, but a new study published in Science quantified for the first time the changes in precipitation during the period. The group of researchers, led by Nicholas Evans of the University of Cambridge, used a new technique to analyze the isotopes of water trapped in gypsum in Lake Chichankanab.
Gypsum forms when the water level in a lake falls during droughts; the water molecules trapped in this mineral contain the oxygen and hydrogen isotopes needed to measure the amount of water present at the time. Researchers built a model of hydrogeological conditions and found that annual rainfalls at the time fell from 41-54%, with periods of up to 70% less precipitation than normal, which would have affected agriculture and, ultimately, decimated this civilization.