The ancient Rapa Nui civilization may have created the Easter Island statues because they believed these monoliths made the soil more fertile, improving crop production, researchers have said.
In a study published in the Journal of Archaeological Science, an international team of researchers say analysis of statues located within a quarry on Easter Island shows this soil was particularly fertile, and that the civilization appears to have used it to grow banana, sweet potato and taro.
There are almost 1,000 statues across Easter Island. They were carved from soft volcanic rock between around 1200 and 1600. Their purpose is still a mystery, with various ideas on why this civilization built them, why they were erected in certain spots and what they represent.
Easter Island was first inhabited by a small group from Eastern Polynesia around 1,000 years ago. The civilization thrived, reaching a peak of between 15,000 and 20,000. By the time Europeans arrived in the 1700s, the population had fallen significantly. The introduction of foreign diseases, along with the slave raiding expeditions a century later, eventually led the civilization to collapse.
It had previously been suggested that the Rapa Nui population decline may have been the result of 'eocide,' with the land becoming infertile after being over farmed and poorly managed. However, research increasingly indicates this is not the case, with evidence to suggest the civilization was very aware of the landscape and was managed and manipulated to ensure fertility in poor quality soil.
In the latest research, Sarah Sherwood, from the University of the South, Sewanee, and colleagues, have looked at the soil quality in a key area of the island—Rano Raraku quarry.
Rano Raraku is where the stone for about 95 percent of the island's statues came from. It is on the eastern side of the island and includes two statues—including Moai 156, which is one of only three across the whole island that was embellished with petroglyph motifs.
The two statues are found in the inner region of the quarry. They had been positioned upright, with one on a pedestal and the other in a deep hole. The team say this suggests that the statues were not abandoned at the site, but were positioned there on purpose.
Tests also revealed the soil in Rano Raraku was some of the richest in the whole island. "When we got the chemistry results back, I did a double take," Sherwood said in a statement. "There were really high levels of things that I never would have thought would be there, such as calcium and phosphorous. The soil chemistry showed high levels of elements that are key to plant growth and essential for high yields."
Analysis indicates that sweet potato, banana, taro, paper mulberry and possible bottle gourd were all planted at the site. Researchers believe that the constant movement of land associated with quarrying probably increased the fertility of the soil in this part of the island.
"Everywhere else on the island the soil was being quickly worn out, eroding, being leeched of elements that feed plants, but in the quarry, with its constant new influx of small fragments of the bedrock generated by the quarrying process, there is a perfect feedback system of water, natural fertilizer and nutrients," Sherwood said.
The planting of multiple crops also adds weight to the idea the civilization understood land management—having different crops in the same area helps maintain the fertility of the soil.
Researchers say the Rapa Nui people may have believed the statues helped boost soil fertility, so distributed them around the island accordingly.
Study author Jo Anne Van Tilburg, director of the Easter Island Statue Project, said their research suggests the Rano Raraku statues appear to have been kept where they were built to "ensure the sacred nature of the quarry itself."
"The Moai were central to the idea of fertility, and in Rapanui belief their presence here stimulated agricultural food production," she said in a statement. "Our excavation broadens our perspective of the Moai and encourages us to realize that nothing, no matter how obvious, is ever exactly as it seems. I think our new analysis humanizes the production process of the Moai."
