Who were the first Americans? Where did they come from, and when? These are questions some scientists say Kennewick Man can help answer.

Leading theorists suggest three routes for human settlement of the Americas.

Overland route:
About 12,000 to 14,000 years ago, towards the end of the Ice Age, big-game hunters migrated across the Bering land bridge from Siberia to Alaska. They made their way south between continental ice sheets, spreading throughout the Americas. This model and associated artifacts and remains are called Clovis, after the New Mexican town where the first 13,500-year-old artifacts were found. The Clovis model typically envisions a single migration and, until recently, was the widely accepted peopling paradigm.

Coastal route: Evidence of early habitation along the Pacific coast challenges the single migration, overland model. Some scientists argue that migrants from Asia may have worked their way down the American coast by boat. Melting glaciers would have left shorelines relatively hospitable 17,000 years ago. This model considers the possibility of thousands of years of multiple migrations from all over Asia, starting 15,000 to 20,000 years ago.

Atlantic maritime route: This controversial model suggests that some of the first Americans may have arrived from Europe. Pointing to similarities between some North American and 20,000-year-old European tools, proponents suggest migrants may have boated across the Atlantic. Such migrations may have occurred 18,000 to 24,000 years ago.