EarthScience Wire

New study helps sort out Easter Island mystery

Photo credit: Phil Whitehouse/Flickr
Monolithic human figures called moai were carved from rock between 1250 and 1500 by the inhabitants of Easter Island, which lies more than 2,000 miles off the coast of Chile. Photo credit: Phil Whitehouse/Flickr

A new study by an international team of geographers and archeologists is helping to understand what caused the population collapse of the Rapa Nui – the early inhabitants of Easter Island.

The 63-square-mile island, which lies more than 2,000 miles off the west coast of Chile, was settled around 1200 AD, and the Rapa Nui population is thought to have reached as high as about 15,000. But by 1722, when Europeans arrive, the population had declined to about 2,000, and it was nearly gone by the 1860s.

The catalyst for the Rapa Nui’s demise has long been debated in the scientific community. Was environmental degradation the cause, or could a political revolution or an epidemic of disease be to blame?

The new research, published in the Proceedings of the National Academy of Sciences, suggests that the demise of the Polynesia group began before the arrival of the Europeans arrived in 1722. The study also suggests that regional variations and natural environmental barriers to growing crops played a factor rather than the inhabitants’ actions degrading the environment.

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Oliver Chadwick is a professor in University of California at Santa Barbara’s Department of Geography and the Environmental Studies Program. He said:

In the current Easter Island debate, one side says the Rapa Nui decimated their environment and killed themselves off. The other side says it had nothing to do with cultural behavior, that it was the Europeans who brought disease that killed the Rapa Nui. Our results show that there is some of both going on, but the important point is that we show evidence of some communities being abandoned prior to European contact.

The archaeologists examined six agriculture sites used by the island’s statue-building inhabitants. Their research focused mainly on the three sites for which they had information on climate, soil chemistry and land use trends as determined by an analysis of obsidian spear points.

The team used flakes of obsidian, a natural glass, as a dating tool. Measuring the amount of water that had penetrated the obsidian’s surface allowed them to gauge how long it had been exposed and to determine its age. Chadwick said:

When we evaluate the length of time that the land was used based on the age distribution of each site’s obsidian flakes, which we used as an index of human habitation, we find that the very dry area and the very wet area were abandoned before European contact. The area that had relatively high nutrients and intermediate rainfall maintained a robust population well after European contact.

The study results suggest that the Rapa Nui reacted to regional variations and natural environmental barriers to producing sufficient crops rather than degrading the environment themselves. In the nutrient-rich center where they could produce food well, they were able to maintain a viable culture even under the threat of external factors, say the researchers, including European diseases such as smallpox, syphilis and tuberculosis. Chadwick said:

The pullback from the marginal areas suggests that the Rapa Nui couldn’t continue to maintain the food resources necessary to keep the statue builders in business. So we see the story as one of pushing against constraints and having to pull back rather than one of violent collapse.

Bottom line: New research suggests a combination environmental degradation and the arrival of Europeans contributed to the collapse of Easter Island’s Rapa Nui society.

Read more from University of California at Santa Barbara

February 2, 2015

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