New study increases mystery of Cahokia migration. newswise

From the line: Chris Woolston

Newswise – Nine hundred years ago, the cahokia mounds The settlement, located just across the Mississippi River from present-day St. Louis, is populated by approximately 50,000 people in the metropolitan area, making it one of the largest communities in the world. However, by 1400, the once-popular site was practically deserted, a mass departure that is shrouded in mystery.

One popular theory is that Cahokia residents abandoned the settlement after a massive crop failure due to a prolonged drought. But a new study in the journal The Holocene Natalie MuellerCaitlin Rankin, PhD ’20, assistant professor of archeology in Arts & Sciences at Washington University in St. Louis, suggests that the Cahokians may have had other reasons for leaving the city.

Rankin dug deep into the soil at the historic Cahokia site to collect isotopes of carbon, atoms left over from plants growing when human populations were decimated and drought was common throughout the Midwest.

All plants use one of two types of carbon, carbon 12 and carbon 13, for photosynthesis, but not all plants photosynthesize in the same way. Plants adapted to dry climates – including prairie grasses and maize, which was an important new crop during the Cahokia period – incorporate carbon into their bodies at a rate that leaves a tell-tale trail when the plants die and decompose. .

Most other plants that the Cahokians would have harvested for food – including squash, goosefoot, and sumpweed – would have left a distinct signature, which they share with plants of wetlands and native forests.

Rankine’s samples showed that the ratio of carbon 12 to carbon 13 remained relatively consistent during that critical period – an indication that there had been no radical change in the types of plants growing in the area. “We saw no evidence that meadow grasses were becoming dominant, which we might have expected in a landscape where there was widespread crop loss,” Mueller said.

Cahokians are known for their ingenuity, and Rankin said they may have had the engineering and irrigation skills to keep crops thriving in difficult conditions. “It’s possible they weren’t really feeling the effects of the drought,” said Rankin, now an archaeologist for the Bureau of Land Management in Nevada.

Mueller said the sophisticated society that developed at Cahokia almost certainly included storage systems for grain and other foods. Residents also enjoyed a varied and diverse diet including fish, birds, deer, bears, and forest fruits and nuts – which would keep them nourished even when some food sources disappeared.

To get a better understanding of the diets and agricultural practices of the indigenous peoples of the Midwest, Mueller hopes to create a database that will collect paleobotanical evidence from across the region. “Gathering that information will help us see if people have turned to different crops in response to climate change,” he said. She also plans to grow some food crops under controlled conditions on the campus to understand how they might have responded to ancient drought and other challenges.

So, why did the Cahokians abandon their abundant lands? Muller suspects that this was a gradual process. “I don’t envision a scenario where thousands of people are suddenly moving out of the city,” she said. “People probably spread out to be closer to relatives or to find different opportunities.”

“They put a lot of effort into building these mounds, but there were probably external pressures that caused them to move,” Rankin said. “The picture is likely complex.”

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