Trampling experiments in the search for the earliest Americans

Experiments were undertaken to evaluate a natural versus cultural origin for a set of modified pebbles and cobbles found in pre-Clovis-age contexts at the Big Eddy site (23CE426) in southwest Missouri, U.S.A. Two experiments involving Asian elephants and American bison provided evidence that pre-Clovis-age modified cobbles, pebbles, and flakes probably were produced by the trampling of large mammals traversing alluvial gravel bars in search of food and water in a riparian environment. The production of zoofacts and behavioral aspects of elephants are described with respect to research on the earliest Americans

Bayesian chronological analyses consistent with synchronous age of 12,835-12,735 Cal B.P. for Younger Dryas boundary on four continents

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835–12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer