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
Pre-Columbian rafts It was during these trade voyages that South American sailors may have introduced metallurgy to Mexico. The purported trade between Ecuador and Mexico consisted of luxury items, including Spondylus (spiny oyster) and Strombus (conch) shells, which were prominently traded from their origins in the warm ocean waters of Ecuador throughout the Andes and up and down the coasts of South America. Since the voyage of the Kon-Tiki in 1947, there have been numerous crossings of the Pacific Ocean by raft from South America to Polynesia. In the 1990s, four attempts to sail a raft from Ecuador to Mexico failed, although