Deep Layers of Ancient Human Poop Were Found at the Bottom of an Illinois Lake

Monks Mound, the largest pre-Columbian earthwork in the Americas, was left by a large civilization that also left a lot of poop. Skubasteve834/Wikimedia Commons

When our civilization has crumbled, our waste will remain to tell our story. Landfills, graveyards, and even our excrement will reveal more about us to future archaeologists than any collapsed skyscraper ever could.

It was no different for the great civilizations that came before us. Learning about their rise and fall sometimes requires looking beyond just the cultural artifacts and fallen architecture they left behind. It requires digging deeper, into the... muckier... layers of ancient human remains.

Forget about their pyramids; look for their poop.

That's the philosophy behind a new effort by researchers studying Cahokia, a famed prehistoric city near present-day St. Louis. To better understand the factors that led to the collapse of this once-magnificent Native American metropolis, archaeologists have been studying ancient soil layers beneath Horseshoe Lake in Illinois, which sits right next to some of Cahokia's most famous structures, reports

A bit unexpectedly, researchers are discovering that those soil layers also happen to contain a lot of poop. And that poop is beginning to tell a fascinating story about what happened to the people who once lived and thrived here.

As the people of Cahokia pooped on land, that poop found its way through runoff, streams, and groundwater flow into the lake. Because the sediments of a lake accumulate in layers, it provides a calendar of sorts that archaeologists can flip through to study changes that occur over time. Each poop layer is like a tree ring, and it leaves vital clues to what was happening over the years in this ancient city.

One of the things that can be looked at is population. The thicker the fecal layer in a given year, the more people that were likely pooping and occupying the city. Thus, researchers have been able to determine that human occupation of Cahokia intensified around A.D. 600, and it continued to grow through 1100, when the city reached its peak population. Tens of thousands of people probably called it home at this point.

Something likely happened by 1200, however, because Cahokia's population began to decline around this time. By 1400 the site was all but abandoned. All of these dates coincide with what archaeologists have surmised from other more traditional methods of establishing timelines.

Sediment layers have a lot more to say than just what their poop content tells us, however. Lake cores also help to piece together environmental changes over time that help explain why populations may have risen or fallen. In this case, researchers were able to date a major flood in the nearby Mississippi River around the year 1150, which might have contributed to population loss around the site.

Other environmental factors, like lower summer precipitation patterns, can also be seen in the sentiment cores. This would have made growing maize, which was Cahokia's main crop, more difficult.

Taken all together, researchers are beginning to piece together exactly what happened to this city and why it was eventually abandoned.

"When we use this fecal method, we can make these comparisons to environmental conditions that hither to now we haven't really been able to do," explained lead author AJ White.

It's all information that researchers might not have been able to put together in quite so detailed a fashion if it wasn't for looking for poop at the bottom of a lake. It might not be the most glamorous part of being an archaeologist, but it's all in the interest of getting closer to the truth. And in science, that's what matters most.