Mystery of Easter Island's Moai is SOLVED: Giant stone monoliths helped food grow on the land by replenishing the soil with nutrients

Easter Island in Polynesia is famed for its mysterious carved figures known as Moai, which the indigenous Rapanui people believed helped food grow on the land.

Now new analysis of the quarry where more than 90 per cent of the monoliths were created - Rano Raruko - suggests that they may have been right.

In a five-year study of two Moai monuments at the centre of Rano Raruko, experts at UCLA found that the carving process itself, which took place in during the 13th–16th centuries, turned the quarry into an agricultural oasis.

Creating hundreds of the heads churned up layers of soil and brought nutrient-rich bedrock to the surface.

This, together, with an abundant freshwater supply, allowed banana, taro and sweet potato to flourish on the the land.  

Analysis of chemicals in the soil around the Moai revealed the soil was far more fertile than anywhere else on the Polynesian island. 

The Moai were made at Rano Raruko before being moved elsewhere on the island, except for a few which stayed in the quarry for ceremonial purposes. 

Two Moai that remained in the quarry were excavated as part of a five-year project by UCLA researcher Jo Anne Van Tilburg, director of the Easter Island Statue Project on Rapa Nui.

'Our excavation broadens our perspective of the Moai and encourages us to realise that nothing, no matter how obvious, is ever exactly as it seems. I think our new analysis humanises the production process of the Moai,' Dr Van Tilburg said. 

Excavations at Rano Raruko are highly restricted, with the digs for this study being the first to get the go-ahead since 1955. 

Soils in the quarry were already thought to be the richest on the entire Polynesian island thanks to a fresh water supply.

But it received a significant boost as the carving of the Moai themselves increased its richness, the researchers believe.

Bedrock unearthed by workers as they toiled in the quarry was rich in clay and then returned to the topsoil, providing essential nutrition for crops.   

Extensive chemical testing of the soil around the heads revealed the presence of calcium and phosphorous - key chemicals for plant growth. 

Professor Sarah Sherwood, from the University of the South in Tennessee, was involved in the chemical analysis of the soul. 

'When we got the chemistry results back, I did a double take,' Professor Sherwood said. 

'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. 

'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 fertiliser and nutrients.' 

The two Moai analysed in the study were carefully selected due to where they were and how they were placed.   

They had been almost completely buried by soil and found in the inner quarry between 1510 and 1645, it is thought. 

Both were upright, with one on a pedestal and one in a deep hole, indicating they were meant to remain there, the researchers say. 

'We chose the statues for excavation based on careful scrutiny of historical photographs and mapped the entire Rano Raraku inner region before initiating excavations,' Dr Van Tilburg said. By Joe Pinkstone