Clam Shells Tell Ancient Story

Geologist Researches Climate-Induced Downfall of Advanced Civilization

clam shells

By analyzing these sea shells, researchers in the College are learning more about historical impacts of climate change on residents of sixth-century Peru.

From the April 2013 Desktop News | Analyses of clam shells used in ancient funeral ceremonies offer additional evidence as to how climate change may have contributed to the gradual collapse of an early South American civilization, according to Dr. Fred Andrus, an associate professor in the Department of Geological Sciences.

His research, which was published online in the scientific journal Geology, indicates El Niño, a temporary, cyclical change in the Pacific Ocean’s circulation, and an intertwined ocean phenomenon, known as upwelling, likely contributed to the sixth-century downfall of an advanced Peruvian civilization called the Moche.

The Moche once flourished along the northern coast of Peru around 540 A.D. But the civilization collapsed after their primary food sources were altered. Andrus, along with the article’s lead author Dr. Miguel Etayo-Cadavid, one of Andrus’ former doctoral students, believes the change in food source can be attributed to a phenomenon known as upwelling, a wind-driven phenomenon that brings deep water and nutrients back to the ocean’s surface, which would have caused the seafood the Moche ate to diminish.

“In the case of the Moche, much of their protein was derived from the sea,” Andrus said. “They had specialized fishermen with trade and transfer of fish between people. If you change the fishery, like we think occurred with them, that is going to have a domino effect through the people, ending on their dinner table.”

Key to the research was the recovery and analysis of clam shells the Moche presented to their dead during funeral ceremonies held nearly 1,500 years ago, Andrus said. Clam shells used in the research were recovered from well preserved Moche burial sites at Huaca de la Luna, near the modern city of Trujillo in northern Peru. Through radiocarbon dating of the shells and other materials left in the excavated tombs and by studying the archaeological contexts of the burial tombs, the scientists can estimate the shells’ age and the relative amount of upwelling that occurred when the shells grew.

Through chemical analysis of the shells’ growth bands — which form somewhat similarly to tree rings — the scientists are able to determine what some of the environmental conditions were like during the lifespan of the clams. The process of combining the shells’ known age with the derived environmental conditions occurring during its lifetime to develop conclusions of long ago conditions is an example of a field of science known as sclerochronology.

Research indicates the Moche faced periods of more frequent, more intense El Niño conditions with cycles lasting longer than what commonly occurs now. The deep water upwellings were likely reduced by the extended El Niño conditions, Andrus said.

“Perhaps this upwelling shift didn’t strike people as of equal importance as the flood waters washing their fields away, but rather was a subtle and fairly long-lasting change,” Andrus said. “The Moche example shows how unforeseen changes to the climate and environment under which a society has flourished may trigger profound political transformations within it.”