Lake Sediments Record Climate Change At Cahokia INDIANAPOLIS, INDIANA —National Public Radio reports that climatologist Broxton Bird of Indiana University-Purdue University Indianapolis and colleagues analyzed layers of calcite crystals interspersed with layers of mud on the bottom of Indiana’s Martin Lake in order to learn about historic rainfall levels at Cahokia. The study suggests that beginning in the 900s, the Central Mississippi Valley received more rain than usual. And carbon isotopes found in skeletons at Mississippian cities indicate that people ate a lot of corn. “That comes at right around 950, and that’s around the time the population at Cahokia...