Climate Drove Southwest Native Cultural Changes
Reuters News Service, Oct. 5, 2001
Using mineral bands in stalagmites from New Mexican caves to track climate change over the past 4,000 years, scientists have found that wet and dry periods helped drive major cultural shifts among ancient people in the American Southwest.
Agricultural advances, such as the introduction of corn and cotton in the region, the debut of ceramics and the abandonment of the famed pueblo cliff dwellings, all correlate closely to changes in climate, scientists said on Thursday in a study appearing in the journal Science.
University of New Mexico researchers Victor Polyak and Yemane Asmerom studied cave formations called stalagmites — upward-growing columns made of minerals, in this case calcite, deposited over eons by dripping water. They differ from stalactites, their cousins that hang from cave ceilings. They retrieved five stalagmites from two caves in New Mexico's Guadalupe Mountains — the renowned Carlsbad Caverns and the less-famous Hidden Cave about 15 miles away.
Polyak and Asmerom used an advanced dating technique and the thickness of layers of calcite deposited on the stalagmites to reconstruct the region's precipitation record year by year dating back to almost 2000 B.C. Thicker bands meant more moisture in a given year.
"As water seeps from the surface, through the soils and through the bedrock and down into the cave, you get a drip-by-drip deposition of calcium carbonate (calcite)," Polyak said in an interview.
The researchers then compared this climate information to the archeological record.
"We noticed that at certain times, there was a change in our band thickness (indicating a wetter or drier period). And this would correspond to a change in the cultural history," Polyak added. "We made a correlation between cultural change and climate change using these stalagmites."
HISTORICAL CLIMATE FLUCTUATIONS
The Anasazi people of the American Southwest who lived in the region are the ancestors of modern Pueblo Indians.
From about 2000 B.C. to 1000 B.C., they made a transition from a nomadic hunter-gatherer existence to establish settlements and early agricultural efforts, Polyak said.
Polyak said that change coincided with the onset of wetter conditions in the region. The study found that the rise of corn agriculture in the region took place during a particularly wet time just under 3,000 years ago.
Thinner layers of calcite in the stalagmites revealed the onset of a slightly drier period starting about 300 A.D. This coincided with the first appearance of ceramics — which supplanted traditional baskets — and the introduction of cotton, the researchers said.
Another wetter spell that lasted from about 750 A.D. to 900 A.D. coincided with population expansion. During this time, the native people moved from so-called pit houses, which were circular, covered pits used as shelters and storage areas, into above-ground dwellings.
Population redistribution took place during a more arid period that started in at 900 A.D. and then became increasingly wet until about 1100 A.D. only to dry up again 50 years later.
Settlements moved from mesa tops into open valleys, canyon heads or natural rock alcoves and people began to build huge multistory, multiroom masonry structures called pueblos.
The onset of a significantly drier climate in about 1330 A.D. coincided with abandonment of higher elevation dwellings and population migration to river areas.
Even during the wettest periods, the region remained relatively arid, but even subtle
precipitation changes seemed to influence local culture, Polyak said.
"For people who live in the Southwest, they can really understand that dry conditions can really change things out here. And so can wet conditions," Polyak said. "It doesn't take that much of an increase in precipitation or a lowering of temperature to change things."
"One of the lessons would be that our climate can influence our culture," Polyak said. "That's something that's serious."