US History: Early America, Lesson One – The Land Bridge Theory The Land Bridge Theory Do you ever wonder where the first Americans came from? The Land Bridge Theory is one idea of how people first appeared on this continent. It states that Native Americans migrated from Asia to North America across the land bridge during the Ice Age. During this time period, low temperature caused the level of water in the ocean to drop. Because the frozen water caused the level of the oceans to drop, the land that once was under water became exposed, creating a long land bridge that connected North America to Asia. By following herds of animals, hunter-gatherer people may have crossed this land bridge from Asia into North America and then continued throughout many generations across North America and even spreading into South America. It is believed that the people we call “Native Americans” are the descendents of these first huntergatherers from Asia.