The real mystery behind Moana: After 1,700 years, why did Polynesians suddenly sail east?

The same question drives both the plot of Moana and decades of archaeological research: Why, after centuries of relative stability, did Polynesian voyagers suddenly begin settling islands thousands of kilometers away across the Pacific? The latest Moana movie is a live-action adaptation of a Disney animated movie of the same name. While the films are fictional, they draw inspiration from the rich seafaring heritage of Polynesian peoples, whose ancestors undertook one of the greatest episodes of maritime exploration in human history. New climate evidence may help us understand why they embarked on these voyages. The backdrop to Moana is the mystery of the “long pause”. This was a period when Polynesian ancestors, the Lapita people, sailed east into the Pacific as far as the island archipelagos of Samoa and Tonga, arriving around 3,000 years ago. They brought with them distinct pottery styles and an island-based culture. While ancestral Polynesians were highly adaptable and accustomed to seasonal droughts, prolonged and severe droughts during times of high population density might mean an island could no longer support its human population. Ultimately, island survival hinges on a single critical resource: rainfall. Until recently, scientists lacked evidence from the Tonga and Samoa region of what the climate was like in this critical migration era. But we were able to reconstruct these past changes by analyzing hydrogen isotopes—slightly different forms of the same element—preserved in ancient mud from swamps and lakes. In the tropics, the isotopic composition of rainwater reflects the amount of rainfall. As algae and plants grow and absorb this water, they lock this chemical signature into molecules that can survive in sediment for thousands of years, providing a natural archive of past rainfall. Using this technique, we found evidence of a sustained, severe dry period in the southwest tropical Pacific between 850 and 1200 AD. Our results, recently published in the Journal of Pacific Archaeology, indicate this was the driest period the region had experienced in the past 2,000 years. Crucially, this drought coincided with a time when island populations were larger. The great migration into the eastern Pacific coincided with a dry climate in the western Pacific: