Strait edge dating
The pre-LGM warm cycles in Arctic Siberia saw flourishes of megafaunas.The oxygen isotope record from the Greenland Ice Cap suggests that these cycles after about 45k years BP lasted anywhere from hundreds to between one and two thousand years, with greater duration of cold periods starting around 32k cal years BP.
this site is likely just an interesting paleontological locality." Chris Stringer said that "extraordinary claims require extraordinary evidence - each aspect requires the strongest scrutiny," adding that "High and concentrated forces must have been required to smash the thickest mastodon bones, and the low energy depositional environment seemingly provides no obvious alternative to humans using the heavy cobbles found with the bones." It is possible that a small founder population had entered Beringia before that time.Alpine glaciers in the coastal ranges and the Alaskan Peninsula isolated the interior of Beringia from the Pacific coast.Coastal alpine glaciers and lobes of Cordilleran ice coalesced into piedmont glaciers that covered large stretches of the coastline as far south as Vancouver Island and formed an ice lobe across the Straits of Juan de Fuca by 15,000 Prior to the Last Glacial Maximum, climates in eastern Siberia fluctuated between conditions approximating present day conditions and colder periods.While much of the coastal plain was covered with piedmont glaciers, unglaciated refugia supporting terrestrial mammals have been identified on Haida Gwaii, Prince of Wales Island, and outer islands of the Alexander Archipelago.Coastal areas deglaciated rapidly as coastal alpine glaciers, then lobes of Cordilleran ice, retreated.A drop of eustatic sea level by about 60 m to 120 m lower than present-day levels, commencing around 30,000 years BP, created Beringia, a durable and extensive geographic feature connecting Siberia with Alaska.
With the rise of sea level after the Last Glacial Maximum (LGM), the Beringian land bridge was again submerged.
The abandonment of the northern regions of Siberia due to rapid cooling or the retreat of game species with the onset of the LGM has been proposed to explain the lack of archaeosites in that region dating to the LGM.
The pollen record from the Alaskan side shows shifts between herb/shrub and shrub tundra prior to the LGM, suggesting less dramatic warming episodes than those that allowed forest colonization on the Siberian side.
Models of molecular evolution rates are used to estimate the ages at which Native American DNA lineages branched off from their parent lineages in Asia and to deduce the ages of demographic events.
One model based on Native American mt DNA Haplotypes (Figure 2) proposes that migration into Beringia occurred between 30k and 25k cal years BP, with migration into the Americas occurring around 10k to 15k years after isolation of the small founding population.
However, archaeosites that date closer to the Last Glacial Maximum on either the Siberian or the Alaskan side of Beringia are lacking.