Easter Island’s famed statues have long captivated our imaginations . . . and our practical minds.
How did the monolithic giants get there? How were they built?
Now a new study has worked out how Polynesian architects were able to mount 13-tonne red hats on their heads.
The island in the Southern Pacific Ocean is thought to have been first inhabited in the 13th century by Polynesian travellers.
Its statues, carved from volcanic tuff, came from one quarry, while the hats, made of red scoria, came from a quarry on the other side of the island.
Previous research has determined that the statues, which can be up to 10m tall and weigh 81 tonnes, were moved into place along well-prepared roads using a walking and rocking motion, similar to the way a fridge might be moved.
The hats, each weighing 13 tonnes, might have been rolled across the island, but once they arrived at their intended statues, they still needed to be lifted on to the statues’ heads.
The islanders probably carved the hats cylindrically and rolled them to the statues before further carving them to their final shapes, which vary from cylindrical to conical and usually have a smaller cylindrical projection on the top.
“We were interested in figuring out the method of hat transport and placement of the hats that best agrees with the archaeological record,” Pennsylvania State University’s Sean Hixon said.
The researchers took multiple photographs of many hats to see what attributes were the same throughout.
The only features they found the same were indentations at the bases of the hats, and these indentations fit the tops of the statues’ heads.
If the hats had been slid into place on top of the statues, then the soft stone ridges on the margin of the indentations would have been destroyed.
Previous researchers suggested that the statues and the hats were united before they were lifted into place, but the remnants of broken or abandoned statues suggested this wasn’t the approach used.
More likely, the hats were raised to the top of standing statues, using large ramps. But, once the hat was at the top of the ramp, it could not simply be pushed into place because of the ridges on the margin of the hat base indentation.
Rather, the researchers believe the hats were tipped up on to the statues, where they could be rotated using levers.
Easter Island and climate change
Another strange study, partly drawing on Easter Island, asks whether sustainability is possible.
Astronomers have inventoried a sizeable share of the universe’s stars, galaxies, comets, and black holes.
But does the universe contain planets with sustainable civilisations?
Or does every civilisation that may have arisen in the cosmos last only a few centuries before it falls to the climate change it triggers?
A group of researchers have tackled the question from an astrobiological perspective.
“Astrobiology is the study of life and its possibilities in a planetary context,” said Professor Adam Frank, of the University of Rochester.
“That includes exo-civilisations or what we usually call aliens.”
By thinking of civilisations and planets — even alien ones — as a whole, researchers can better predict what might be required for the human project of civilisation to survive.
“The point is to recognise that driving climate change may be something generic,” Frank said.
“The laws of physics demand that any young population, building an energyintensive civilisation like ours, is going to have feedback on its planet.
“Seeing climate change in this cosmic context may give us better insight into what’s happening to us now and how to deal with it.”
Using their model, the researchers found four potential scenarios that might occur in a civilisation-planet system.
They included mass “die-off ” survived by only a fraction of the world’s population; a shift to a sustainable future that avoided the most catastrophic effects; a population collapse that came without any change to the world’s resources; or a population collapse that came in spite of a late shift to sustainability.
“The last scenario is the most frightening,” Frank said.
“Even if you did the right thing, if you waited too long, you could still have your population collapse.”
The researchers created their models based in part on case studies of extinct civilisations, such as the inhabitants of Easter Island.
People began colonising the island between 400AD and 700AD and grew to a peak population of 10,000 sometime between 1200AD and 1500AD.
By the 18th century, however, the inhabitants had depleted their resources and the population dropped drastically to about 2000 people.
The Easter Island population die-off related to a concept called carrying capacity, or the maximum number of species an environment can support.
The Earth’s response to civilisation building is what climate change is really all about, Frank said.
“If you go through really strong climate change, then your carrying capacity may drop, because, for example, large-scale agriculture might be strongly disrupted.”
He issued a sober warning. “If you change the Earth’s climate enough, you might not be able to change it back.”