Chronology Settlement of the Americas

map of americas showing pre clovis sites.

in 21st century, models of chronology of migration divided 2 general approaches. first short chronology theory, first migration occurred after last glacial maximum, went decline after 19,000 years ago, , followed successive waves of immigrants. second theory long chronology theory, proposes first group of people entered americas @ earlier date, possibly 21,000–40,000 years ago, followed later second wave of immigrants. further controversy has been generated age-dating of archaeosites in americas , timing of opening of ice-free corridor have challenged clovis first theory, dominated thinking on new world anthropology of 20th century.

archaeological evidence

figure 2. schematic illustration of maternal (mtdna) gene-flow in , out of beringia (long chronology, single source model).



figure 3. illustration of hypothetical chronology migration through beringia (long chronology model). not authoritative on timing of glacial features , not constrained archaeological data.

pre-last glacial maximum migration across beringia americas has been proposed explain purported pre-lgm ages of archaeosites in americas such bluefish caves , old crow flats in yukon territory, , meadowcroft rock shelter in pennsylvania. earlier c date bone artifact @ old crow flats site has been supplanted accelerator mass spectrometry c date indicates holocene age. interpretations of butcher marks , geologic association of bones @ bluefish cave , old crow flats sites have been called question. ages of earliest positively identified artifacts @ meadowcroft site constrained compiled age estimate c in range of 12k-15k c years bp (13.8k-18.5k cal years bp). meadowcroft rockshelter site , monte verde site in southern chile, date of 14.8k cal years bp, archaeosites in americas oldest dates have gained broad acceptance.

stones described probable tools, hammerstones , anvils, have been found in southern california, @ cerutti mastodon site, associated mastodon skeleton appeared have been processed humans. mastodon skeleton dated thorium-230/uranium radiometric analysis, using diffusion–adsorption–decay dating models, 130.7 ± 9.4 thousand years ago. no human bones found, , claims of tools , bone processing have been described not plausible . michael r. waters commented demonstrate such occupation of americas requires presence of unequivocal stone artefacts. there no unequivocal stone tools associated bones... site interesting paleontological locality. chris stringer said extraordinary claims require extraordinary evidence - each aspect requires strongest scrutiny, adding high , concentrated forces must have been required smash thickest mastodon bones, , low energy depositional environment seemingly provides no obvious alternative humans using heavy cobbles found bones.

the yana river rhino horn site (rhs) has dated human occupation of eastern arctic siberia 27k c years bp (31.3k cal years bp). date has been interpreted evidence migration beringia imminent, lending credence occupation of beringia during lgm. however, yana rhs date beginning of cooling period led lgm. but, compilation of archaeosite dates throughout eastern siberia suggest cooling period caused retreat of humans southwards. pre-lgm lithic evidence in siberia indicate settled lifestyle based on local resources, while post-lgm lithic evidence indicate more migratory lifestyle.

the oldest archaeosite on alaskan side of beringia date 12k c years bp (14k cal years bp). possible small founder population had entered beringia before time. however, archaeosites date closer last glacial maximum on either siberian or alaskan side of beringia lacking.

genomic age estimates

recent studies of amerindian genetics have used high resolution analytical techniques applied dna samples modern native americans , asian populations regarded source populations reconstruct development of human y-chromosome dna haplogroups (ydna haplogroups) , human mitochondrial dna haplogroups (mtdna haplogroups) characteristic of native american populations. models of molecular evolution rates used estimate ages @ native american dna lineages branched off parent lineages in asia , deduce ages of demographic events. 1 model based on native american mtdna haplotypes (figure 2) proposes migration beringia occurred between 30k , 25k cal years bp, migration americas occurring around 10k 15k years after isolation of small founding population. model (figure 3) proposes migration beringia occurred approximately 36k cal years bp, followed 20k years of isolation in beringia. yet model proposes migration beringia occurred between 40k , 30k cal years bp, pre-lgm migration americas followed isolation of northern population following closure of ice-free corridor. 3 native american mtdna evolution rate models fall within long chronology theory of migration americas.

a study of diversification of mtdna haplogroups c , d southern siberia , eastern asia, respectively, suggests parent lineage (subhaplogroup d4h) of subhaplogroup d4h3, lineage found among native americans , han chinese, emerged around 20k cal years bp, constraining emergence of d4h3 post-lgm. age estimates based on y-chromosome micro-satellite diversity place origin of american haplogroup q1a3a (y-dna) @ around 10k 15k cal years bp. greater consistency of dna molecular evolution rate models each other , archaeological data may gained use of dated fossil dna calibrate molecular evolution rates.