In the history of human exploration, the settlement of East Polynesia ranks among the most remarkable achievements. While Western Polynesia, settled almost 3,000 years ago, is relatively accessible from Asia, the islands of the eastern Pacific are far more remote. Finding them in the small craft available to the Polynesians at the time, without compasses or sextants, was almost like going to the Moon. Evidence from the island of Atiu reveals some of these voyages were earlier than previously suspected, and provides a strong hint of what drove them.
Atiu is in what is now called the Cook Islands although the name is changing. The first settlers are thought to have come from Tonga or Samoa across around 1,000 kilometers (600 miles) of open ocean. Even this astonishing voyage was just the first step of the even more remarkable journey to Rapa Nui (Easter Island).
The timing of the first arrivals has been in doubt, but Professor David Sear of the University of Southampton has analyzed core samples collected from mud in a lake on Atiu. For most of the 6,000 years of mud sampled, there were no signs of mammals (the islands fruitbats apparently leaving no mark), but around 900 CE Sear detected a surge in mammalian feces. He attributes this to visits by humans and their pigs, 100-200 years before most previous estimates, but Sear thinks the island was initially used as a waystation, not a permanent home.
Within a century, other signs of human activity emerged as forest was burnt to make space for crops. Sear also found a burst of microcharcoals around 1,400 years ago, which could indicate a brief settlement, or burning further afield.
In Proceedings of the National Academy of Sciences Sear and co-authors compare Atiu's sediments with cores collected from Samoa and Vanuata. They found the arrival at Atiu coincided with the driest period in the last 2,000 years in the islands of origin, as rainbands shifted north.
The authors conclude the temporarily dry islands could no longer support as many people, creating an incentive to find new locations. Meanwhile, the accompanying wind shift made eastward sailing easier. Once the rain systems returned to their usual state, island populations boomed and settlement thrived throughout the eastern Pacific.
"Today, changing climate is again putting pressures on Pacific island communities, only this time the option to migrate is not so simple,” Sear said in a statement. Cook Islanders are citizens of New Zealand, so if their islands become uninhabitable through rising sea levels they have somewhere to go. However, most of the population of Polynesia lack such an escape route, unless the nations whose actions are destroying the island people's homes choose to open their doors.