Atoll islands are areas of low, flat land, and the sustainability of habitable land in such environments is sensitive to even slight changes in sea level. The projected rise in sea level during this century may lead to the submergence of atoll islands and the widespread loss of habitable land. However, the actual time sequence of past sea level change, island emergence events, and human settlement of newly emerged islands remain poorly constrained. The results of geomorphological and archaeological surveys, combined with calibrated radiocarbon age dates, at Majuro Atoll, Marshall Islands, central Pacific, reveal that the emergence of the island, triggered by a fall in sea level, was quickly followed by human settlement. The elevation of the central body of the island exceeded high water level at 2000 years CalBP, and the complete formation of the island occurred within an interval of 100 years. The island was colonized by people shortly after emergence, at 2000 years CalBP, prior to the establishment of dense vegetation, and has been continuously settled since that time.