Share it! Science : Debunking Easter Island Mysteries with Obsidian Flakes and Tooth Plaque

Wednesday, January 28, 2015

Debunking Easter Island Mysteries with Obsidian Flakes and Tooth Plaque

     It has long been debated what caused the mysterious decline of the native population of Rapa Nui, or Easter Island. The prevailing, and conflicting, theories up until this point were that the native people decimated their fragile environment and eventually starved, and the other is that the natives died quickly of diseases brought by the Europeans. Although we will never be 100% sure of what happened on this mysterious Polynesian island known for its giant stone heads, we might be getting closer to knowing the truth. 
Moai on Easter Island Photo: Phillie Casablanca
     A team of soil scientists and archaeologists recently examined several agricultural sites on the island. They analyzed flakes of obsidian from spear points at three different sites to help understand climate, soil chemistry and land use. They were able to date the land use at each of the sites based on how much water had been absorbed into the surface of the obsidian. The amount of water absorption allowed them to estimate how long the surface had been exposed.
      In general the soil nutrient levels of Easter Island were less than other islands settled by Polynesians during the same time period. However, the three sites examined indicated a lot of diversity in the quality of the land for agriculture. The soil at the first site on the northwestern coast of the island was dry and high in nutrients. This part of the island was in the rain shadow of a volcano and therefore didn't receive much rainfall. The next site, on the interior of the island, had more rainfall, but less nutrient rich soil. The third, on the northeast coast, was more of a "Goldilocks" site, an average amount of rainfall and fairly high soil nutrients.
      The team determined through analysis of the dates of land use at the three locations that the native population of the island most likely abandoned the dry and nutrient poor sites long before European contact, and maintained a population at the site with average rainfall and quality soil long after European contact. The results of this study indicate that rather than using the land beyond their means and then dying off, the natives adapted by moving to an area that was more sustainable for agriculture. They were able to maintain their way of life in this area for a while despite the pressures of diseases introduced by the Europeans such as smallpox, syphilis and tuberculosis. This evidence should change the thinking of many from a tale of violent population collapse to a slow adaptation and decline.
      The story of the people of Rapa Nui has so many mysteries, including their primary diet. Many anthropologists are now using the dental plaque of ancient peoples to understand what they were eating. The native's diet has been a bit of a puzzle as there was conflicting evidence around palm being a dietary staple. Scientists have found many palm phytoliths, a hardened silica fossil plants leave behind in the soil, in the dental plaque of the natives of Easter Island. Other evidence indicates that palms went extinct on the island soon after humans colonized the area. So what were they eating? Further analysis of teeth from remains excavated in the 1980's show that the plaque contained starches that were almost identical to modern sweet potato. They did not find evidence of other starchy foods that had been hypothesized to be part of the prehistoric populations diet, such as banana, taro or yams. Upon further research with sweet potatoes and similar soil it has been found that the skin of the sweet potato takes in the phytoliths of palms as it grows in the soil. Hence, it is now understood that the palm evidence on the teeth is most likely related to their diet of sweet potatoes, clearing up the mystery of the palm phytoliths.
      No doubt our theories and understanding of prehistoric people on Easter Island and other locations will continue to grow. We will never know for sure what happened in these places, but the allure of the mystery drives us to learn more!

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