Coastal environments during the Last Glacial Maximum were complex.
The lowered sea level, and an isostatic bulge equilibrated with the depression beneath the Cordilleran Ice Sheet, exposed the continental shelf to form a coastal plain.
The uncertainty is fed by a lack of archaeological evidence along migration routes that date to the periods when those migrations are proposed to have occurred; uncertainties in the dating and interpretation of the oldest proposed archaeosites in the Americas; and uncertainties of assumptions underlying chronological and source models of migration derived from studies of modern Native American genetics.
are the archaeosites in the Americas with the oldest dates that have gained broad acceptance.
The variation of the eustatic sea level with time has been reconstructed using oxygen isotope analysis of deep sea cores, the dating of marine terraces, and high resolution oxygen isotope sampling from ocean basins and modern ice caps.The continents of North and South America were settled by natives from Asia between 10 and 20 thousand years ago after they crossed a land bridge that formed between Alaska and far northeastern Siberia due to the lowering of sea level during the last ice age.Available scientific evidence indicates that modern humans emerged from Africa over 100,000 years ago, yet did not arrive in the Americas until less than 20,000 years ago.The retreat was accelerated as sea levels rose and floated glacial termini.Estimates of a fully ice-free coast range between 16k While most of the archaeological community is in general agreement that the Americas were settled by migrants from northeastern Asian populations, the chronology of the migrations, the source populations that contributed to the migrations, and their migration routes remain uncertain.