Ancient poop helps show climate change contributed to fall of Cahokia

Ancient poop helps show climate change contributed to fall of Cahokia
Cahokia region and Horseshoe Lake watershed, shown as the black dashed line. Dark brown colors indicate higher topography, principally the river bluffs, and the yellow indicates the Mississippi River floodplain. Coring sites are indicated by red stars. The Cahokia complex is approximated by the large circle around black rectangles showing the position of some of the mounds at the site. Black dots show the locations of other sites with mounds within the Horseshoe Lake watershed that were occupied contemporaneously with Cahokia [∼1000–1400 CE]. Base map elevation data are derived from the National Elevation Dataset. Credit: PNAS (2019). 10.1073/pnas.1809400116

A new study shows climate change may have contributed to the decline of Cahokia, a famed prehistoric city near present-day St. Louis. And it involves ancient human poop.

Published today [Feb. 25, 2019] in the Proceedings of the National Academy of Sciences, the study provides a direct link between changes in Cahokia's as measured through a unique fecal record and showing evidence of drought and flood.

"The way of building population reconstructions usually involves , which is separate from the data studied by ," explains lead author AJ White, who completed the work as a graduate student at California State University, Long Beach. "One involves excavation and survey of archaeological remains and the other involves lake cores. We unite these two by looking at both kinds of data from the same lake cores."

Last year, White and a team of collaborators—including his former advisor Lora Stevens, professor of paleoclimatology and paleolimnology at California State University, Long Beach, and University of Wisconsin-Madison Professor of Anthropology Sissel Schroeder—showed they could detect signatures of human poop in lake core sediments collected from Horseshoe Lake, not far from Cahokia's famous mounds.

These signatures, called fecal stanols, are molecules produced in the human gut during digestion and eliminated in feces. As the people of Cahokia pooped on land, some of it would have run off into the lake. The more people who lived and defecated there, the more stanols evident in lake sediments.

Because the sediments of a lake accumulate in layers, they allow scientists to capture snapshots of time throughout the history of a region through sediment cores. Deeper layers form earlier than layers found higher up, and all of the material within a layer is roughly the same age.

White found that fecal stanol concentrations at Horseshoe Lake rise and fall similarly to estimates of Cahokia's population from better-established archaeological methods.

Schroeder, a scholar of the Cahokia area, says that excavations of the houses in and near Cahokia show human occupation of the site intensified around A.D. 600, and by 1100, the six-square-mile city reached its peak population. At the time, tens of thousands of people called it home.

Archaeological evidence also shows that by 1200, Cahokia's population was on the decline and the site was abandoned by its mound-building Mississippian inhabitants by 1400.

Scientists have uncovered a number of explanations for its eventual abandonment, including social and political unrest and environmental changes.

For instance, in 2015, co-author Samuel Munoz, a former UW-Madison graduate student and now a professor at Northeastern University, was actually the first to collect one of the Horseshoe Lake sediment cores White used in his study and he found evidence that the nearby Mississippi River flooded significantly around 1150.

White's latest study ties the archaeological and environmental evidence together.

"When we use this fecal stanol method, we can make these comparisons to environmental conditions that hither to now we haven't really been able to do," says White, now a Ph.D. student at UC Berkeley.

Using Munoz's core and another White collected on Horseshoe Lake, the research team measured the relative amount of fecal stanols from humans present in sediment layers. They compared these to stanol levels known to come from bacteria in the soil in order to establish a baseline concentration for each layer.

They examined the lake cores for evidence of flooding and also looked for climate indicators that would inform them whether climate conditions were relatively wet or dry. These indicators, the ratio of a heavy form of oxygen to a light one, can show changes in evaporation and precipitation. Stevens explains that as water evaporates, the light form of oxygen goes with it, concentrating the heavy form.

The core showed that summer precipitation likely decreased around the onset of Cahokia's decline. This could have affected the ability of people to grow their staple crop maize.

A number of different changes begin to happen in the archaeological record around 1150, Schroeder explains, including the number and density of houses and the nature of craft production.

These are all indicators of "some kind of socio-political or economic stressors that stimulated a reorganization of some sort," she says. "When we see correlations with climate, some archaeologists don't think climate has anything to do with it, but it's difficult to sustain that argument when the evidence of significant changes in the climate shows people are facing new challenges."

This has resonance today, she adds.

"Cultures can be very resilient in face of but resilience doesn't necessarily mean there is no change. There can be cultural reorganization or decisions to relocate or migrate," Schroeder says. "We may see similar pressures today but fewer options to move."

For White, the study highlights the nuances and complications common to so many cultures and shows how environmental change can contribute to social changes already at play.


Explore further

Scientists can measure population change through chemicals found in feces

More information: A.J. White el al., "Fecal stanols show simultaneous flooding and seasonal precipitation change correlate with Cahokia's population decline," PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1809400116
Citation: Ancient poop helps show climate change contributed to fall of Cahokia (2019, February 25) retrieved 19 October 2019 from https://phys.org/news/2019-02-ancient-poop-climate-contributed-fall.html
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Feb 25, 2019
This is interesting because future historians will be able to use the open elimination of human waste in America's cities as a tool to see how Republican Misrule and outright treason destroyed the American state.

Feb 25, 2019
It's amazing to know that feces preserve the environmental conditions. But, nowadays the feces are processed in the plant. Due to human intervention (i.e. processing), I am not sure if it will preserve the true environmental indicators a millennium later.

Feb 25, 2019
"A new study shows climate change may have contributed to the decline of Cahokia, a famed prehistoric city near present-day St. Louis."
Er, Cahokia was certainly not .. prehistoric. I don't think a city that existed between 600 and 1350 AD could possibly considered "prehistoric", even by Native American standards. I believe the correct term is "pre-Columbian".


Feb 25, 2019
to see how Republican Misrule and outright treason destroyed the American state

Because Democrats are so much better at running states. Lemme see, of the 20 states with the least fiscal debt, 18 are "red" states. Of the states with the most fiscal debt, only 5 are "red" states.

https://www.goban...-debt/#3

But fiscal responsibility doesn't mean skimping on education. Utah ranks 3rd for quality of education, while 7th lowest fiscal debt, 10th for quality of healthcare.

To be fair, Democrats do much better when they run cities.

https://www.weste...america/

https://www.usnew...d-states

Whoops. I guess not.

Feb 26, 2019
Waiting for the true blue backlash against the: racist, sexist, BS the Left is pushing.

Feb 26, 2019
"A new study shows climate change may have contributed to the decline of Cahokia, a famed prehistoric city near present-day St. Louis."
Er, Cahokia was certainly not .. prehistoric. I don't think a city that existed between 600 and 1350 AD could possibly considered "prehistoric", even by Native American standards. I believe the correct term is "pre-Columbian".



"pre-historic" simply means "pre-dating a written record". As writing was introduced in different places at different times, the end of the pre-historic era also varies from place to place. In Mesopotamia, the historical era begins around 3100 BC, in north-western Europe it's around the start of the 1st century AD, in Australia it's 1788 AD.

In common parlance, people generally take "prehistoric" as referring to an absolute period, up to roughly the rise of ancient Greek civilization, but that's not how historians use the term. The use of "pre-historic" in this article is actually fully correct.

Feb 26, 2019
Or maybe, as Jared diamond explained, it was the euro diseases intentionally spread by the first explorers. 'Intentionally' is my word, not his. When settlers arrived only a few gens later the fields were overgrown, the people had largely disappeared, and the civilization was gone.

The article is more sick politics from delusional academies.

Feb 26, 2019
And, in other news.
Modern AGW Cult Bullshit, will be the downfall of the Cult.

Feb 26, 2019
Not sure if this passes the, ahem, sniff test... ;)

Feb 27, 2019
I never realized before, just how strongly I desire to see the word "poopulation" used in a scientific paper.

otto, if I understand the postulated timeline in this article?
Cahokia was already depopulated & abandoned by the time the first Spanish & French missionaries & explorers showed up in the Lower Mississippi region.

Without mounted & wheeled transportation, the city's inhabitants were limited in range for hunting & collecting firewood.

Compared to just a couple of hundred years before? By 1200, the landscape around Cahokia must have looked pretty barren.

Similar to the ecological disaster the original Pueblo cities brought onto themselves.

The multitude of diseases introduced by europian savages were just a poisonous icing on a rancid cake.

As a follow-up to this research. It would be interesting to compare DNA from the Cahokia site with that of Early Plains (pre-horse) peoples. I have a theory those may have been refugee survivors from dying cities?

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