The Meadowcroft Rockshelter Radiocarbon Chronology 1975-1990

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Abstract
Ever since the publication of the first of more than 50 internally consistent radiocarbon dates from Meadowcroft Rockshelter (36 WH297), controversy has been generated by frequent assertions that the dates older than 11,000 B.C. have suffered particulate or nonparticulate contamination. Data bearing on these assertions are assessed in the light of accelerator mass spectroscopy (AMS) dates provided by Oxford University. The weight of all data taken together suggests that this site still represents the best-dated evidence for the presence of human beings south of the glacial front in the Americas. That evidence indicates that Native Americans were present in southwestern Pennsylvania by 14,000–14,500 years ago.