Polynesian navigation snow. In the mid-20th century, Thor Heyerdahl proposed a new theory of Polynesian origins (one which did not win general acceptance), arguing that the Polynesians had migrated from South America on balsa-log boats. The presence in the Cook Islands of sweet potato that is a plant native to the Americas (called "kūmara" in Māori), which have been radiocarbon-dated to 1000 CE, has been cited as evidence that Americans could have traveled to Oceania. The current thinking is that sweet potato was brought to central Polynesia circa 700 CE and spread across Polynesia from there, possibly by Polynesians who had traveled
Tuamotuan language they were settled c. 700 AD by people from the Society Islands. Europeans first discovered the islands in 1521, when Ferdinand Magellan reached them while sailing across the Pacific Ocean. Subsequent explorers visited the islands over the centuries, including Thor Heyerdahl, the famous Norwegian ethnographer who sailed the Kon-Tiki expedition across the Pacific in 1947. The effects of early European visits were marginal as they had no political effects. The language, however, was ultimately affected by the Tahitian language, which was itself affected by European expansion. The eventual arrival of European missionaries in the 19th century also led to loanwords,