Easter Island statues made farms more fertile

Science News investigates the benefits of carving monumental heads and burying their bottom halves in the ground. It seems like they might have had a ceremonial purpose linked to farming – because they increase soil fertility, and the ground around them seems to have grown a lot of Polynesian produce:

Soil analyses indicate that weathering of volcanic sediment created by quarrying enriched the slopes of Easter Island’s major rock quarry with phosphorus and other elements crucial for farming. Microscopic plant remains suggest that food grown in the enriched soil included sweet potatoes, bananas, taro, paper mulberry fruit and probably bottle gourd, say anthropological archaeologist Sarah Sherwood and colleagues.

The new study is “one more piece of evidence against the traditional story of Easter Island’s self-inflicted environmental demise,” says Sherwood, of the University of the South in Sewanee, Tenn.

Cultivation occurred in many parts of Rapa Nui before European contact, says archaeologist Carl Lipo of Binghamton University in New York. Investigators need to determine whether any other sites on the island contained soil as productive as that at the statue quarry, he suggests.

Findings from Sherwood’s group help to show how Rapa Nui was transformed from a palm forest into a cultivated terrain that supported islanders for more than 500 years, Lipo says. Quarry cultivation “adds to growing knowledge of how pre-contact people smartly utilized their landscape,” he says. Related research has found that, as palm forests shrank on Rapa Nui, farmers cultivated yams and other crops using clever techniques such as rock gardens that fortified soil quality.

Crescent shapes and other figures carved on statues’ backs, and a carved human head found resting against the base of one statue, suggest that these objects were used in ceremonies of some kind, perhaps intended to promote crop growth.

Researchers traditionally have assumed that builders of the island’s partially buried quarry statues had either planned to move them elsewhere on the island or abandoned them.

There’s more on the team’s findings in the Journal of Archaeological Science here.