expansion into the Pacific was eastward, against steady trade winds. Sailing against the wind, he argues, may have been the key to their success. "They could sail out for days into the unknown secure in the knowledge that if they didn't find anything, they could turn about and catch a swift ride home on the trade winds." For returning explorers, successful or not, the geography of their own archipelagoes provided a safety net, ensuring that sailors wouldn't sail past and be lost again in the open ocean. Vanuatu, for example, is a chain of islands 800 kilometers(500 miles) long with many islands within sight of each other. Once sailors hit that string of islands, they could find their way home Irwin hypothesizes that once out in the open ocean, the explorers would detect a variety of clues to follow to land: seabirds and turtles that need islands on which to build their nests coconuts and twigs carried out to sea, and the clouds that tend to form over some islands in the afternoon. It is also conceivable that Lapita sailors followed the smoke from distant volcanoes to new islands.