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The environment during the latest Pleistocene[ edit ] For an introduction to the radiocarbon dating techniques used by archaeologists and geologists, see radiocarbon dating. Emergence and submergence of Beringia[ edit ] Figure1. As water accumulated in glaciers, the volume of water in the oceans correspondingly decreased, resulting in lowering of global sea level.
The variation of sea level over 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.
Estimates of the final re-submergence of the Beringian land bridge based purely on present bathymetry of the Bering Strait and eustatic sea level curve place the event around 11, years BP Figure 1.
Ongoing research reconstructing Beringian paleogeography during deglaciation could change that estimate and possible earlier submergence could further constrain models of human migration into North America. By 21, years BP, and possibly thousands of years earlier, the Cordilleran and Laurentide ice sheets coalesced east of the Rocky Mountains, closing off a potential migration route into the center of North America. 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, 14C years BP 18, cal years BP.
Diverse, though not necessarily plentiful, megafaunas were present in those environments. Herb tundra dominated during the LGM, due to cold and dry conditions.
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 retreat was accelerated as sea levels rose and floated glacial termini. Estimates of a fully ice-free coast range between 16k  and 15k  cal years BP. Littoral marine organisms colonized shorelines as ocean water replaced glacial meltwater. Eustatic sea level rise caused flooding, which accelerated as the rate grew more rapid. Opening of an ice-free corridor did not occur until after 13k to 12k cal years BP. 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.
Chronology[ edit ] Map of the Americas showing pre Clovis sites. In the early 21st century, the models of the chronology of migration are divided into two general approaches. Archaeological evidence[ edit ] Figure 2. Schematic illustration of maternal mtDNA gene-flow in and out of Beringia long chronology, single source model.
Illustration of hypothetical chronology for migration through Beringia long chronology model. Not authoritative on timing of glacial features and not constrained by archaeological data. Stones described as probable tools, hammerstones and anvils , have been found in southern California, at the Cerutti Mastodon site , that are associated with a mastodon skeleton which appeared to have been processed by humans.
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Waters commented that "To demonstrate such early occupation of the Americas requires the presence of unequivocal stone artefacts. There are no unequivocal stone tools associated with the bones However, archaeosites that date closer to the Last Glacial Maximum on either the Siberian or the Alaskan side of Beringia are lacking. Genomic age estimates[ edit ] For more details on this topic, see Genetic history of indigenous peoples of the Americas.
Recent studies of Amerindian genetics have used high resolution analytical techniques applied to DNA samples from modern Native Americans and Asian populations regarded as their source populations to reconstruct the development of human Y-chromosome DNA haplogroups yDNA haplogroups and human mitochondrial DNA haplogroups mtDNA haplogroups characteristic of Native American populations.
One model based on Native American mtDNA 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.
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The development of high-resolution genomic analysis has provided opportunities to further define Native American subclades and narrow the range of Asian subclades that may be parent or sister subclades. For example, the broad geographic range of Haplogroup X has been interpreted as allowing the possibility of a western Eurasian, or even a European source population for Native Americans, as in the Solutrean hypothesis , or suggesting a pre-Last Glacial Maximum migration into the Americas.
Subhaplogroups D1 and D4h3 have been regarded as Native American specific based on their absence among a large sampling of populations regarded as potential descendants of source populations, over a wide area of Asia. Its parent lineage, Subhaplotype D4h, is believed to have emerged in east Asia, rather than Siberia, around 20k cal years BP. The descendants of source populations with the closest relationship to the genetic profile from the time when differentiation occurred are not obvious.
Source population models can be expected to become more robust as more results are compiled, the heritage of modern proxy candidates becomes better understood, and fossil DNA in the regions of interest is found and considered. A report published in the American Journal of Physical Anthropology in January reviewed craniofacial variation focussing on differences between early and late Native Americans and explanations for these based on either skull morphology or molecular genetics.
Arguments based on molecular genetics have in the main, according to the authors, accepted a single migration from Asia with a probable pause in Berengia, plus later bi-directional gene flow. Studies focussing on craniofacial morphology have argued that Paleoamerican remains have "been described as much closer to African and Australo-Melanesians populations than to the modern series of Native Americans", suggesting two entries into the Americas, an early one occurring before a distinctive East Asian morphology developed referred to in the paper as the "Two Components Model".
A third model, the "Recurrent Gene Flow" [RGF] model, attempts to reconcile the two, arguing that circumarctic gene flow after the initial migration could account for morphological changes. It specifically re-evaluates the original report on the Hoya Negro skeleton which supported the RGF model, the authors disagreed with the original conclusion which suggested that the skull shape did not match those of modern Native Americans, arguing that the "skull falls into a subregion of the morphospace occupied by both Paleoamericans and some modern Native Americans.
They have a distribution ranging from coastal east Asia to the Pacific coast of South America. Historically, theories about migration into the Americas have centered on migration from Beringia through the interior of North America.
The discovery of artifacts in association with Pleistocene faunal remains near Clovis, New Mexico in the early s required extension of the timeframe for the settlement of North America to the period during which glaciers were still extensive. That led to the hypothesis of a migration route between the Laurentide and Cordilleran ice sheets to explain the early settlement. The Clovis site was host to a lithic technology characterized by spear points with an indentation, or flute, where the point was attached to the shaft.
A lithic complex characterized by the Clovis Point technology was subsequently identified over much of North America and in South America. The association of Clovis complex technology with late Pleistocene faunal remains led to the theory that it marked the arrival of big game hunters that migrated out of Beringia then dispersed throughout the Americas, otherwise known as the Clovis First theory.
Recent radiocarbon dating of Clovis sites has yielded ages of Numerical dating of Clovis sites has allowed comparison of Clovis dates with dates of other archaeosites throughout the Americas, and of the opening of the ice-free corridor.
Both lead to significant challenges to the Clovis First theory. The Monte Verde site of Southern Chile has been dated at Pre-LGM closing of the corridor may approach 30k cal years BP and estimates of ice retreat from the corridor are in the range of 12 to 13k cal years BP. The interior route is consistent with the spread of the Na Dene language group and Subhaplogroup X2a into the Americas after the earliest paleoamerican migration. Coastal migration Pacific models propose that people first reached the Americas via water travel, following coastlines from northeast Asia into the Americas.
Coastlines are unusually productive environments because they provide humans with access to a diverse array of plants and animals from both terrestrial and marine ecosystems. Two cultural components were discovered at Monte Verde near the Pacific coast of Chile.
The older and more controversial component may date back as far as 33, years, but few scholars currently accept this very early component. A recent variation of the coastal migration hypothesis is the marine migration hypothesis, which proposes that migrants with boats settled in coastal refugia during deglaciation of the coast. A coastal east Asian source population is integral to the marine migration hypothesis. The data indicate that Anzick-1 is from a population directly ancestral to present South American and Central American Native American populations.
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Anzick-1 is less closely related to present North American Native American populations. D4h3a has been identified as a clade associated with coastal migration.
Certain types of evidence dependent on organic material, such as radiocarbon dating, may be destroyed by submergence. Wave action can destroy site structures and scatter artifacts along a prograding shoreline. Additionally, Pacific coastal conditions tend to be unstable due to steep unstable terrain, earthquakes, tsunamis, and volcanoes. Strategies for finding earliest migration sites include identifying potential sites on submerged paleoshorelines, seeking sites in areas uplifted either by tectonics or isostatic rebound, and looking for riverine sites in areas that may have attracted coastal migrants.
In a article in the Journal of Island and Coastal Archaeology, Erlandson and his colleagues proposed a corollary to the coastal migration theory—the "kelp highway hypothesis"—arguing that productive kelp forests supporting similar suites of plants and animals would have existed near the end of the Pleistocene around much of the Pacific Rim from Japan to Beringia, the Pacific Northwest, and California, as well as the Andean Coast of South America.
Once the coastlines of Alaska and British Columbia had deglaciated about 16, years ago, these kelp forest along with estuarine, mangrove, and coral reef habitats would have provided an ecologically similar migration corridor, entirely at sea level, and essentially unobstructed. A DNA analysis of plants and animals suggest a coastal route was feasible.
Paleoindians of the coast[ edit ] See also: Genetic studies of Austronesian peoples and Migration and dispersion of Austronesian peoples to the Americas supported by coconut and sweet potato population genetics The boat-builders from Southeast Asia Austronesian peoples may have been one of the earliest groups to reach the shores of North America. The Haida nation on the Queen Charlotte Islands off the coast of British Columbia may have originated from these early Asian mariners between 25, and 12, years ago.
Early watercraft migration would also explain the habitation of coastal sites in South America such as Pikimachay Cave in Peru by 20, years ago disputed and Monte Verde in Chile by 13, years ago [6 30; 8 ]. Migrants, he said, could have then skirted the tidewater glaciers in Canada right on down the coast. Finding sites associated with early coastal migrations is extremely difficult—and systematic excavation of any sites found in deeper waters is challenging and expensive.
On the other hand, there is evidence of marine technologies found in the hills of the Channel Islands of California , circa 10, BCE. Another problem that arises is the lack of hard evidence found for a "long chronology" theory. Y-DNA among South American and Alaskan natives[ edit ] The micro-satellite diversity and distribution of a Y lineage specific to South America suggest that certain Amerindian populations became isolated after the initial colonization of their regions.