for National Geographic News
A big shift in climate has been implicated in the fall of yet another civilization.
According to a report published in the July issue of the journal Geology, ancient civilizations of Peru collapsed at least in part because of a change in the weather pattern known as El Niño.
Indigenous people who lived on the coast of northern Peru began building large temple complexes about 5,800 years ago. The development of their culture, as seen in the elaborate temple building and public art discovered in the area, occurred even before the pyramids in Egypt were built.
The Peruvians continued building the complexes for nearly 3,000 years. But evidence indicates that around 2800 B.C., the sites were abandoned. Scientists working in Peru think they know why.
"We found that there was a change in the frequency of El Niño events about 3,000 years ago and that this correlates in time with cultural change," said Daniel Sandweiss, an archaeologist at the University of Maine who is a member of the team that has been conducting the research.
Other Examples
The idea that climate change can play a role in the rise and fall of civilizations is not new. Other studies have suggested that climatic events such as drought and flooding rains contributed to the downfall of early civilizations in Central and North America, Greenland, and the Middle East.
The climatic factor linked with the collapse of ancient settlements in Peru is the recurrent weather pattern known as El Niño. It occurs as a result of ocean and wind currents in the tropical Pacific, which lead to large-scale oceanic warming. The phenomenon induces major changes in weather patterns around the world, bringing drought, increased rainfall, and flooding in some areas.
In recent times El Niño has happened every two to seven years. Until the last quarter of this century, it occurred every seven to fifteen years.
But Sandweiss and his colleagues believe the pattern was quite different several thousand years ago.
Evidence from Shells
Evidence of El Niño's role in the collapse of ancient Peruvian settlements lies in mollusk shells found in middens—essentially trash piles—found at the sites. "We use the disappearance of some species and appearance of others in the middens as indicators of general frequency ranges," Sandweiss explained.
Mollusks are good indicators of climate because they are sensitive to temperature changes.
Two species of mollusk—Mesodesma donacium and Choromytilus chorus—were common in the middens of coastal Peru. But by 2,800 years ago, they had virtually disappeared.
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