Extensive ancient coastline allowed peopling of America earlier than thought

Extensive ancient coastline allowed peopling of America earlier than thought

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A new paleogeography study suggests that the West Coast of North America looked radically different than scientists previously thought.  The study, led by Jorie Clark of Oregon State University, has taken a new look at the West Coast’s sea level history.



The first human migrants from Asia to North America crossed the now submerged land bridge of Beringia (probably after a lengthy stopover) and traveled down the West Coast as long as 15,000 years ago.  The melting of the massive continental ice sheets following the Last Glacial Maximum around 21,000 years ago caused sea levels to rise by around 430 feet, submerging vast expanses of the continental shelf and any archaeology that sat on them.

Past models assumed that global sea levels rose in concert with the melting ice sheets (known as ‘the bathtub model’), but the new study says that this was not the case.

Professor Clark explained: “During the last deglaciation, sea level rise was significantly influenced by the weight of the large ice sheets, which depressed the land under and near the ice sheets.  As the ice sheets melted, this land began to rise. At the same time, the weight of the water melting from the ice sheets and returning to the oceans also depressed the ocean basins.  This exchange of mass between ice sheets and oceans led to significant differences in sea level at any given location from the assumption of a uniform change.”

New models of sea level rises over the last 20,000 years, based on ice sheet dimensions and ocean floor topography, concluded that the West Coast would have looked vastly different than models had previously predicted.  For example, the central Oregon shelf, thought to have been a small island chain around 14,000 years ago, may actually have been a solid land mass with an extensive coastline.

Professor Clark said: “There has been new evidence that the peopling of the Americas happened earlier than was long thought to be the case, which has put a lot of focus on coastal paleogeography.  This new look at sea level changes helps explain how that earlier introduction into the Americas could be possible.  It is also important for predicting where coastal villages that are now submerged on the continental shelf may be located.”

West Coast of North America - image from Google Earth
West Coast of North America – image from Google Earth

Sources:  Journal of Archaeological ScienceAlbany Democrat Herald

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