One of the enduring mysteries of world history is whether the Americas had any contact with the Old World before Columbus, apart from the brief Viking settlement in Newfoundland. Many aspects of higher civilisation in the New World, from the invention of pottery to the building of pyramids, have been ascribed to European, Asian or African voyagers, but none has stood up to scrutiny.
The one convincing piece of evidence for pre-Hispanic contact has been the humble sweet potato, which is of tropical American origin but widely cultivated across the Pacific islands. Until a few years ago it was assumed that this was the result of Spanish transmission, dating to the early colonial period, but archaeological discoveries in the Cook Islands show this to be wrong: excavations at Mangaia yielded carbonised remains of sweet potato (Ipomoea batatas) dating to AD1000, five centuries before Europeans entered the Pacific Ocean.
They modeled accidental and natural drift patterns from South/Central America to various points in the Pacific. Must read this paper.