A growing body of evidence suggests that humans reached the Americas prior to 15,000 years ago, and possibly much earlier. The merging of the Laurentide and Cordilleran ice sheets during the Last Glacial Maximum (LGM), beginning 26,000 years ago, would have left no inland corridor open for transit until about 14,000 years ago, which leaves two possibilities: either humans entered via the ice-free corridor before the onset of the LGM or a coastal route was used. Both options suffer from a degree of archaeological invisibility, as no pre-LGM American archaeological site has been widely accepted and any archaeological record for the Pleistocene coast has been drowned by subsequent sea-level rise. In the absence of hard archaeological evidence, modelling plausible routes and timings has become an important research pathway. Writing in Proceedings of the National Academy of Sciences USA, Praetorius et al. turn to palaeo-oceanographic modelling and palaeoenvironmental data from the North Pacific to identify windows in which the climate for a coastal route hugging the Cordilleran ice sheet would have been favourable. They identify 24,500–22,000 and 16,400–14,800 years before present as sweet-spot periods during which winter sea ice would have connected islands and coastal refugia, and ice-free summers would have yielded productive marine environments. Although the Pleistocene watercraft necessary to traverse a coastal route have yet to be found in Beringia or the Cordilleran coastal route, the authors point out that maritime technologies existed at the far end of what has sometimes been termed the ‘kelp highway’ in Asia by 35,000 years ago. Narrowing down the windows during which coastal travel might have been best facilitated can guide future searches for archaeological sites.
Original reference: Proc. Natl Acad. Sci. USA 120, e2208738120 (2023)
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