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FARMINGTON — After evaluating data from nearly 30,000 tree ring samples, archaeologists now believe they can shed new light on what led to social changes in ancestral Puebloan communities.

A study published in this month's issue of the journal Science Advances links climate change and inequality to social disruption in the ancient societies that inhabited the Four Corners from 500 to 1400.

Researchers evaluated the communities based on tree ring samples in a University of Arizona collection. They found four periods of booms and busts in the construction of villages. Those periods coincided with societal changes that created four distinct eras. Archaeologists refer to these as the Basket Maker III and Pueblo I, II and III eras.

Periods of increased development "represent a period where something really clicks for these people," said Tim Kohler, one of the study's senior authors and an anthropology professor at the Washington State University in Pullman, Wash. These "booms" led to the establishment of villages with large populations.

Drought periods may not have had a big influence on small societies, but they could have been devastating to large villages that depended on dry-land corn farming, Kohler said. In societies where leaders performed ceremonies intended to bring rain, prolonged drought could cause social disruption.

"It delegitimizes those leaders and, in fact, their whole way of life," Kohler said.

That kind of upheaval could have also led to changes in leadership.

"When the rains don't come for several years in a row, people turned on those leaders," said Kyle Bocinsky, another senior author of the study who now works at Crow Canyon Archaeological Center in Cortez, Colo.

High inequality among communities can also lead to social change, Bocinsky said.

"We should never underestimate the pernicious affect of inequality in a society," he said.

Eventually, ancestral people left their villages and relocated farther south, settling in the northern Rio Grande region.

Kohler thinks multiple factors led to this exodus. One of the issues was an "almost continuous drought."

Between 1220 and 1250, large numbers of ancestral Puebloan people immigrated to villages in southwestern Colorado's Mesa Verde because the area was not experiencing as severe of a drought as the surrounding region.

The region depended on corn, a tropical plant that grows best in warm weather and water. Facing a depletion of large game, the ancestral Puebloans began raising a new source of protein — turkeys that were fed corn —  after the year 1000.

A period of colder weather from 1300 to 1800 made it more difficult to grow corn, leading to a shortage of food for both people and animals, Kohler said.

Then a drought hit the region. That, combined with an influx of hostile nomadic people from the north, is what Kohler believes led to the exodus. People left the area for the more drought-resistant river valleys along the north Rio Grande.

During this time period, there was also an increase in violence, Kohler said. In 2014, he published a study in the journal American Antiquity examining violence in the central Mesa Verde region compared to the northern Rio Grande.

While ancestral Puebloan society was obviously much different than modern society, Kohler said there are two main lessons people today can learn from the ancient civilizations: the importance of a diverse economy and striking a balance between periods of exploitation and exploration. He defined exploitation as continuing to take actions that are proven to yield results, while exploration refers to experimenting with new methods that may or may not work.

"Don't get too locked into the way you're doing things," Kohler said.

Bocinsky also draws lessons from the study that can be applied to modern society. Much like ancestral Puebloans held their leaders responsible for attracting rain, Bocinsky said modern people hold their elected officials responsible for the state of the economy.  A prime example, he said, was the recession that started in late 2007.

"When that went down, we started asking questions," he said.

Hannah Grover covers Aztec and Bloomfield, as well as general news, for The Daily Times. She can be reached at 505-564-4652.

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