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When and how did the first people come to the Americas? The conventional story says that the earliest settlers came via Siberia, crossing the now-defunct Bering land bridge on foot and trekking through Canada when an ice-free corridor opened up between massive ice sheets toward the end of the last ice age. But here's a dominant, new theory: The first Americans took a coastal route along Alaska's Pacific border to enter the continent. A new geological study provides compelling evidence to support this hypothesis. By analyzing boulders and bedrock, a research team shows that part of a coastal migration route became accessible to humans 17,000 years ago. During this period, ancient glaciers receded, exposing islands of southern Alaska's Alexander Archipelago to air and sun -- and, possibly, to human migration. The timing of these events is key: Recent genetic and archaeological estimates suggest that settlers may have begun traveling deeper into the Americas some 16,000 years ago, soon after the coastal gateway opened up.