The initial colonization of North America: Sea level change, shoreline movement, and great migrations

Abstract

A number of different scenarios have been proposed regarding the origin, timing, and directions initial populations took as they first entered the Americas. In this chapter the major colonization models that have dominated thinking for decades are reviewed, followed by a detailed examination of the role sea level change played in early settlement, with a case study from the southeastern USA. How rapidly shorelines were changing is examined, in meters per year and decade, over 18 time periods from 20,000 to 10,000 cal year BP and along 22 transects running from the modern shoreline to the edge of the continental shelf spaced at roughly 250–300 km intervals from the Texas–Mexico border to the Virginia–North Carolina line. Shoreline movement was neither uniform nor unidirectional, and ranged from a few meters to hundreds of meters per decade, conditions that would have likely influenced human settlement. Shoreline movement was, on average, much faster along the Gulf of Mexico where the continental shelf was broader and more gently sloping than on the South Atlantic seaboard. Shoreline movement was comparatively minor in most areas from the Last Glacial Maximum until the onset of the Bølling-Allerød and MWP-1A, for several hundred years after MWP-1A, and again for several hundred years towards the end of the Younger Dryas. Much greater shoreline movement is evident during MWP-1A, at the end of the Bølling-Allerød and the initial centuries of the Younger Dryas, and during MWP-1B. Variation in coastal environments may help explain the lower incidence of Middle Paleoindian Clovis sites and isolated finds on the modern Gulf as opposed to South Atlantic Coastal Plains, and the increased use of interior areas during the Late Paleoindian period in parts of the region.