|19 January 2019
Early Human Presence In Alaska
Genetic evidence shows that the first peoples of the Americas emerged from a group descended from East Asians and ancient North Eurasians before becoming isolated beginning around 23,000 to 20,000 years ago, coinciding with a period of global cooling and desertification called the Last Glacial Maximum. Because of this many geneticists think that isolation happened in Beringia, and data showing that refuges in Beringia were warmer and more hospitable than most of southern Siberia support this view. Differences in the genomes of their descendants could be explained by limited contact between groups in different refuges.
Archaeological evidence of people living in western Beringia before the Last Glacial Maximum is abundant, yet only one possible human occupation site from that time is known further east; marks on bones from the Bluefish Caves site in the northern Yukon dating to 27,700 years ago have been interpreted by some researchers as evidence of tool use. Lack of archaeological evidence from central and eastern Beringia could mean that people were not living there or that those regions flooded when sea levels rose, or simply because large parts of Alaska and Canada have not been surveyed.
Some archaeologists thnk a group of people may have moved rapidly from Asia into eastern Beringia, where the earliest well-documented human sites are around 15,000 to 14,000 years old. In this "swift peopling" model the isolation happened in Asia, but some archaeologists and most geneticists regard Beringia as a far more likely location.
A new study may help reconcile these views.
Analyses of sediments from a lake in Alaska which was not glaciated during the Last Glacial Maximum reveal an increase in charcoal particles dating to between 32,000 and 19,000 years ago, deposited by fires burning within a few kilometres of the lake. No distinction is possible between natural and artificial fires, but lightning strikes are historically infrequent in the region, and the resistance of steppe vegetation to burning suggests human activity.
In addition, biomarkers called stanols allow identification of the types of animals present; carnivores, omnivores, and herbivores have distinctive profiles; analysis of biomarkers is increasingly used to identify the presence of humans at sites lacking artefacts or remains, and do not require long-term occupation. The researchers identified stanol profiles consistent with the periodic presence of humans in the vicinity of the lake from about 31,000 to 22,000 years ago, and a consistent presence after 18,000 years ago coinciding with greater archaeological visibility of human occupation throughout Alaska. In conjunction with the signs of increased burning, this is very strong circumstantial evidence for an early human presence in eastern Beringia from 32,000 years ago throughout the Last Glacial Maximum.
Edited from Forbes.com (12 January 2019)
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