Britannica Sources used in this answer

Why have many traces of early coastal migration routes disappeared?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A group of Native American men in colorful traditional regalia with feathered headdresses dance outdoors at a powwow ceremony on a grassy field. — Indigenous peoples of the Americas Performers at a Canadian powwow, c. 2008.

Many traces of early coastal migration routes used by the first peoples to enter the Americas have disappeared primarily due to the significant rise in sea level that followed the Pleistocene Epoch.12

During periods of maximum glaciation, such as 18,000 years ago, sea levels were more than 100 meters (328 feet) lower than they are today, exposing vast areas of the continental shelves that served as habitable land. As the last large ice sheets melted, the sea level rose, eventually reaching near-modern levels by the mid-Holocene, about 5,000 years ago. This transgression submerged these former coastal environments, effectively hiding the archaeological evidence of early human arrival beneath the ocean.13

Furthermore, the continental shelves act as dynamic environments where the surf zone continuously erodes and reworks sediments. This process often erases or buries previous traces of human activity, making it difficult to recover evidence of these early coastal migrations. Consequently, researchers must often look to the interior of the continent for evidence of early human presence.43