It was the worst time to be alive, according to some scientists. From 536 C.E. to 541 C.E., a series of volcanic eruptions in North and Central America sent tons of ash into the atmosphere, blocking sunlight, chilling the globe, and destroying crops worldwide. Societies everywhere struggled to survive. But for the Ancestral Pueblo people living in what today is the U.S. Southwest, this climate catastrophe planted the seeds for a more cohesive, technologically sophisticated society, a new study suggests.
“This story makes sense to me,” says Tim Kohler, an archaeologist at Washington State University, Pullman, who has studied climate impacts on the Pueblo people of different eras but was not involved in the new work. He says the disturbance and subsequent reorganization of the Ancestral Puebloans provide clues to what makes societies resilient in the face of dramatic climate change.
At the beginning of the sixth century, some Ancestral Puebloans—ancestors of modern Pueblo people who now live in the U.S. Southwest—grew maize, beans, and squash in small, mobile, kin-based groups across the Colorado Plateau. Other Ancestral Puebloans primarily hunted and foraged for their food, some using the bow and arrow, and others using an ancient spear-throwing technology called an atlatl.
By the turn of the next century, however, the Ancestral Puebloans had had a population boom. They were building large settlements with massive subterranean ceremonial buildings known as great kivas in Chaco Canyon in present-day northwestern New Mexico. The society had adopted large-scale farming, started to raise turkeys en masse, and began to make more durable, high-quality ceramics. Traditionally, researchers have argued this was a slow, gradual transition. But Reuven Sinensky, an anthropology graduate student at the University of California, Los Angeles, who led the new study, and his colleagues uncovered evidence of a much more rapid shift.
Over the course of his research, Sinensky had worked with contemporary Hopi farmers—descendants of the Ancestral Puebloans—and knew that they still employ a number of sophisticated traditional techniques to mitigate the impacts of bad weather, such as early frosts. His experiences led him to wonder how Ancestral Puebloan people might have handled a sudden, prolonged climate crisis.
In the new study, the team looked at 842 radiocarbon dates for the remnants of food sources such as corn cobs, beans, cactus fruits, tree fruits, and wild grains found at 279 sites across the Colorado Plateau. Some dates were previously published, whereas others were measured for the first time using material excavated by Sinensky.
They found that as the fifth century rolled into the sixth, these food bits were found at denser and denser concentrations at Puebloan archaeological sites—a sign that people were growing and gathering more and more food. This pattern dropped off considerably toward the middle of the sixth century, then spiked back up in the late sixth and early seventh centuries, eventually climbing higher than before.
Also, whereas Puebloans in the centuries leading up to about 550 C.E. took a piecemeal approach to growing farming-intensive food such as beans and maize, by the early seventh century they had collectively become expert maize and bean growers.
At higher elevations of the Colorado Plateau, the Ancestral Puebloans chopped down trees to build structures, leaving behind stumps that researchers had previously dated using tree-ring analysis. Based on 1703 tree-ring dates from 141 sites, construction activity appears to have fallen off in the middle of the sixth century, then rebounded at the end of it.
Climate data from tree rings from northern Arizona suggest the region suffered abnormally cold temperatures and drought between the years 534 and 569. So the Ancestral Puebloans, like people around the globe, endured the harsh weather conditions of the time. Yet within a few decades, they had bounced back and reorganized into a larger, more cohesive civilization, the team reported last week in Antiquity.
How did these people weather the storm and then thrive in its aftermath? For one thing, Sinensky says, they had developed techniques for dealing with their region’s weather, which is temperamental even in normal times. Farmers planted crops in a variety of places to boost their chances that at least one would succeed, for example. They also started to work more closely together, coming together to pool labor and resources during harvests and other important agricultural events. “Simply put, cooperation at this scale was not common earlier in time, but quickly became the norm,” Sinensky says.
In addition, whereas the decade or so after the volcanic eruptions proved incredibly taxing for farmers, in the Southwest it was followed by a period of unusually warm, wet weather that would have provided near-perfect growing conditions, Sinensky says.
Although there’s no way to perfectly reconstruct how the Ancestral Pueblo people’s social systems broke down and reformed, Sinensky thinks it may have happened something like this: As crops continued to fail, the small, disparate groups eventually had to band together to survive. They shared technology and growing techniques and built villages. Then, as rain and warmth returned, this cohesion persisted. Chaco Canyon emerged as a major cultural center for a resilient, restructured society.
The findings speak to the ability of humans to reorganize in response to even extreme climate changes, Sinensky adds. “Ancestral Pueblo people restructured … and thrived with this reorganized economic and political structure,” he says. “We should take some solace in knowing that it’s possible to reorganize, to change, even deeply rooted aspects of societies.”
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