Thanks to National Public Radio (USA) and the folks at the salt for raising our awareness of another corn-influenced culture we knew nothing about until just now:
by Angus Chen
About a 15-minute drive east of St. Louis is a complex of earthen mounds that once supported a prehistoric city of thousands. For a couple of hundred years, the city, called Cahokia, and several smaller city-states like it flourished in the Mississippi River Valley. But by the time European colonizers set foot on American soil in the 15th century, these cities were already empty.
Scientists cannot seem to agree on what exactly led to the rise or the fall of this Mississippian American Indian culture, a group of farming societies that ranged from north of the Cahokia site to present-day Louisiana and Georgia. Possible explanations have included massive floods and infighting. But a recent study heaps new evidence on another theory, one contending that changing climate, and its influence on agriculture, were the forces that made the cities flourish, then drove them to collapse.
Cahokia was the largest, and possibly the cultural and political center, of the Mississippian cities, says archaeologist Timothy Pauketat from the University of Illinois, who wasn’t involved in the new study. Researchers have noted that these cities started building roughly around the time of an unusually warm period called the Medieval Climatic Anomaly. And they began declining when the global climate abruptly cooled during a time called the Little Ice Age. “But paleoclimate records from this region weren’t really sufficient to test that hypothesis,” says Broxton Bird, a climatologist from Indiana University-Purdue University Indianapolis, and lead author on the study.
The new evidence comes from ancient layers of calcite (a form of calcium carbonate) crystals buried between layers of mud in Martin Lake in nearby Indiana. The oxygen atoms in each layer of calcite contain information about the amount of rainfall the summer that the layer formed. A higher proportion of oxygen 18, a heavier isotope of the element, suggests greater rains, providing researchers with a year-by-year record of rainfall reaching back hundreds of years.
According to these lake sediments, the Central Mississippi Valley started getting more rain in the 900s. And that’s when corn started thriving. A few decades later, skeletons from several Mississippian cities start showing a distinct carbon isotope signature from corn that suggests people were not only eating corn but eating lots of it. “That comes at right around 950 and that’s around the time the population at Cahokia explodes,” Bird says.
This is around the same time that the city’s great earthwork pyramids started rising. Beside the massive, 10-story Monk’s Mound is a grand plaza that was used for religious ceremonies and for playing the American Indian sport chunkey, involving distinctive stone discs later unearthed by archaeologists. “[Corn production] produces food surpluses,” says Bird. And that allowed the Mississippians to build a society with complex recreation and religious practices, he says.
Cahokia became so notable at this time that other Mississippian chiefdoms may have begun forking off or springing up from its success, says Pauketat. Those other cultural centers were probably copying Cahokia, he says…
Read the whole story here.