Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific breakthroughs and more.
Hundreds of monumental stone heads dot the coast of the remote island of Rapa Nui, or Easter Island, in the Pacific. Settled by a small group of Polynesian sailors around 900 years ago, it’s a fascinating place that has been the subject of fierce debates about how complex societies can sometimes fail disastrously.
Some experts, such as geographer Jared Diamond in his 2005 book “Collapse,” have used Easter Island as a cautionary example of how the exploitation of limited resources can result in catastrophic population decline, ecological devastation, and the destruction of a culture through internal struggles.
Other researchers suggest just the opposite – that Easter Island is the story of how an isolated people created a sustainable system, allowing a small but stable population to thrive for centuries until first contact with European colonial powers in the early 18th century.
Now, research involving remote sensing data and machine learning to map evidence of island agriculture offers a new clue that could help unravel the mysterious disappearance of the island’s original civilization. The new discovery suggests that the island was not densely populated, making ecological collapse a less likely scenario.
“There’s all this evidence collected over the last 15 or 20 years that kind of starts to affect the story of the collapse,” said Dr. Dylan Davis, lead author of the study published Friday in the journal. Science Advances.
“And that’s what this article is based on.”
Easter Islanders used rock gardens
Rapa Nui, now part of Chile, is more than 2,000 kilometers (1,242 miles) from the nearest inhabited island, Pitcairn, and about 3,700 kilometers (2,300 miles) from the South American mainland, according to the study.
Davis, a postdoctoral researcher at the Columbia Climate School’s Lamont-Doherty Earth Observatory, and his team focused on agricultural practices to understand the population size the island could have supported. At 163 square kilometers (63 square miles), it is slightly smaller than Washington, DC.
The rock gardens covered up to 21.1 square kilometers (8.1 square miles) and could have supported up to 17,000 people, previous suggested search. The February 2013 discovery reinforced the idea that people were draining Rapa Nui’s limited resources.
Archaeologists have identified remains of rock gardens where islanders would have grown sweet potatoes and other crops. Scattered and pulverized rocks make land more productive by adding and sealing in nutrients and moisture and protecting young plants from winds – an ancient agricultural technique also known as rock mulching.
However, in the new study, Davis and his colleagues found that the maximum number of people on Rapa Nui was almost 4,000, less than a quarter of that highest estimate.
The team determined the substantially lower population count using a machine learning model trained to identify rock gardens from satellite-collected high-resolution near-infrared and shortwave infrared data.
“What we use in this paper is called shortwave infrared imaging,” Davis said, “and it’s really good at picking up very subtle differences in moisture content and mineralogical changes in the soil.”
The researchers found that rock gardens, identifiable by vegetation patterns and soil composition, covered about three-quarters of 1 square kilometer (0.4 square mile), and the cultivation of rock gardens alone would have sustained around 2,000 people. When combined with estimates of the availability of fish and other marine foods, the team believes that Rapa Nui could have supported a population of 3,901 people.
Davis said the team manually checked the model, which was 83% accurate. “This is good right now because of the data available,” he said. “If there were any obvious errors, we would remove them.”
Another limitation of the approach was the possibility that features of the rock gardens could have been destroyed over the centuries.
What really happened on Easter Island?
Thegn Ladefoged, a professor of archeology at the University of Auckland in New Zealand who led a similar study published in February 2013 that resulted in the highest population estimate, said the latest research provides “new insights into the carrying capacity of ancient Rapa Nui and possible population estimates.”
“Their analysis of newly acquired high-resolution remotely sensed shortwave infrared data found that the total area of rock gardening was 5 to 20 times smaller than previous estimates,” Ladefoged said in an email. “This discovery was the result of integrating new remote sensing data, data not available when we did our original study.” He was not involved in the new research.
“I agree with the authors that a pre-colonial ecocide did not occur on Rapa Nui and that the population did not suffer a collapse.”
However, Christopher Stevenson, professor of anthropology at the School of World Studies at Virginia Commonwealth University, said the machine learning methodology was “far from clear and has not been well evaluated.”
“The authors go out of their way to say how much better their approach is than previous work without actually demonstrating how they deal with the complexities of the dataset,” Stevenson said in an email.
The idea that the island was once home to a population of several thousand people stems from the assumption that large numbers would be needed to build and move the more than 800 enormous stone statues or moai erected throughout the island.
However, a January 2022 Study suggested that it may not have required as much muscular strength as previously thought. Furthermore, although it was initially thought that the islanders cut down trees in part to move the carved heads, a January 2017 study suggested that native palm vegetation be burned to make the soil more fertile.
“Ultimately, we have no proof that thousands and thousands of people lived there. In fact, when Europeans first established contact with the Rapa Nui people, they only reported seeing perhaps 3,000 or 4,000 people and report that people were in good spirits,” Davis said.
“And the real population collapse happens after that, which is probably due to exposure to disease.”
For more news and newsletters from CNN, create an account at CNN.com
