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Cahokia suffers climate change

This article was originally published by Atlas Obscura and is reproduced here as part of the collaboration with Climate Desk.

Never underestimate the power of poo. After more than 1000 years, he can still have a lot to offer.

Just ask the authors of a new study in the Proceedings of the National Academy of Sciences, which explains how the faecal remains can tell us about the ascent and fall of Cahokia, an ancient city located less than 15 km from the current St. Louis, Missouri. According to UNESCO, Cahokia was "the largest pre-Columbian colony in northern Mexico".

Previous excavations of homes in the area, said co-author Sissel Schroeder in a press release, had revealed that the city's population was starting to increase around 600, peaking at 1100 with tens of thousands of people. 39; inhabitants. Things started to change around 12 pm and the city was emptied around 2 pm. AJ White, lead author of the new study and PhD. An archeology candidate from the University of California at Berkeley decided with his colleagues to merge data from the archeological and environmental archives, in the hope of clarifying what had driven the inhabitants of Cahokia.

Naturally, the researchers turned to poop. Of course, more was deposited when more and more people were living in the area. They wondered if the poop dating from the recession could contain clues about what was happening then. To investigate, White and his colleagues examined two cores of sediment collected from Horseshoe Lake in Cahokia. (One was recently dug by White, the other by Samuel Munoz environmental scientist in 2015.) These nuclei contain "fecal stanols", traces of human shit that has derived from the soil towards the lake. Researchers can date carrots because, as they modernize, they appear higher up in the lake.

The team compared levels of fecal stanols to those of other stanols from bacteria in the soil. They found that the more the sediments were rejuvenated, the higher their oxygen concentrations – which meant that the water evaporated with lighter forms of oxygen. In other words, there has probably been less rainfall in the last years of Cahokia – when the excavations showed that there were fewer people living there – thus hampering local agriculture and causing a collapse of the population. The fall of Cahokia, it seems, is at least partly a story of climate change. It is a story that has also been told by other poops, such as those of Incas lamas in the Andes.

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