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Quarried stone fertilised soil for Easter Island inhabitants

The quarrying materials for Easter Island’s giant statues are believed to have contributed to the island’s “horticultural sweet spot”, according to US researchers.

The findings form part of a research project that is investigating the historical impact of the Rano Raraku statue quarry on the island.

Easter Island is one of the world’s most remote inhabited locations, located 3500km west of Chile. It is famous for homing a Polynesian society that erected hundreds of giant statues (moai) sculpted from volcanic rock.

Originating between AD 900 and AD 1100, researchers believe the society suffered in the late 17th century after apparent overuse of the land and deforestation. The island later received its name after Dutch explorers “discovered” it on Easter Sunday in 1722, astounded at the lack of tree life and its small malnourished population.

Now, research in the Journal of Archaeological Science sheds further light on how the inhabitants survived for hundreds of years. They reportedly used labour-intensive rock gardens to increase productivity as soil fertility declined due to deforestation and drought.

Fertilising the soil

According to a Science News report based on the study, the weathering of volcanic rock at Easter Island’s major quarry site fertilised the surrounding soil with phosphorus and other elements to promote crop growth.

Sarah Sherwood, from the University of the South in Sewanee, in Tennessee, USA, said radiocarbon dating of burned wood and plant material recovered from the quarry’s slopes suggests its inhabitants began to farm there between AD 1495 and AD 1585, as soil quality deteriorated on other parts of the island

“Our results confirm a cultivated landscape present on the inner south and east slopes of Rano Raraku [quarry] that included sweet potato and probably bottle gourd along with Polynesian [plant] transfers banana, taro, and paper mulberry from the 14th century AD continuing into the early 19th century AD,” the researchers concluded.

According to the study, there was evidence the statues may have been used in ceremonies to encourage crop growth.

“Rano Raraku [quarry] in sharp contrast had – and still has – extremely fertile soils that are the weathering by-product of lapilli tuff sediments generated from the quarrying process and localised human activity.

“This study validates Rano Raraku as the major moai production centre, establishes chronological parameters for the unique embellished statues and describes agricultural fertility to hypothesise a rich, multi-use landscape for Rano Raraku inner region that is unparalleled elsewhere on [the island].”

CAPTION: Easter Island is world famous for its basalt moai statues.

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