Nature: The Mayan civilization spread across much of modern Mexico and Central America between 300 CE and 1000 CE, but collapsed in the relatively short span of 200 years. What caused the collapse is unknown, but a variety of factors may have contributed. A new study suggests that significant variation in rainfall amounts was one of those factors. A team led Douglas Kennett of the Pennsylvania State University estimated rainfall amounts by measuring radioactive oxygen isotope concentrations in a 2000-year-old stalagmite. The researchers believe that high rainfall from 440 CE to 660 CE prompted a population boom. That was followed by 340 years of protracted droughts that coupled with political instability (determined by records on statues erected during the period) and led to the localized collapse of Mayan city-states and the full collapse of the wider civilization. The technique used for dating the study produced remarkably small error margins compared with previous carbon-dating efforts. However, because the stalagmite only represents localized rainfall, it may not be an accurate representation of empire-wide precipitation patterns.