The mysteries of Easter Island continue to intrigue anthropologists, curious about the ancient residents of the South Pacific island — their nearest neighbors living on Pitcairn Islands 1,297 miles to the west — and the gigantic moai they left behind. How those ancestors came to the island is largely agreed to have been via canoe from Polynesia — not from South America as Thor Heyerdahl famously tested aboard his Kon-Tiki balsa wood raft — but UCSB geologist Oliver Chadwick wanted to know what happened to the civilization that erected the 80-ton statues. Was it European disease that wiped them out? Did they denude their island through over-population?
Chadwick, and his international crew of co-authors of “Variation of Rapa Nui (Easter Island) land use indicates production and population peaks prior to European contact,” published in the Proceedings of the National Academy of Sciences, examined obsidian flakes at three island sites, dating them by the amount of water that had penetrated their surfaces. The three sites, one within a volcanic mountain, were chosen for their varying amounts of rainfall and soil nutrients.
“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,” Chadwick said. “The area that had relatively high nutrients and intermediate rainfall maintained a robust population well after European contact.”
When the Rapa Nui abandoned an area, it was likely more for reasons of a lack of rain and good soil for growing crops. When both were plentiful, the population was able to withstand factors such as European diseases. “So we see the story as one of pushing against constraints and having to pull back rather than one of violent collapse,” Chadwick said, in a UCSB release. The conclusion, as stated in the study title, was that the fluctuations in population predated the arrival of Europeans. The authors also suggest that their study method could be useful in analyzing other prehistoric populations that are believed to have suddenly “collapsed.”