Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis

摘要

Firestone et al. (1) proposed that a cosmic impact-event occurred at the onset of the Younger Dryas (YD) cooling, 12,900 years ago. They reported discovery of enhanced numbers of magnetic microspherules at numerous, widely distributed sites in sediment dating to the YD Boundary (YDB). Spherules were proposed to be either ablated impactor material or terrestrial ejecta from one or more impacts centered on the Laurentide Ice Sheet. Surovell et al. (2) attempted to replicate these results, but found few or no spherules, and Pinter et al. (3) dismissed the spherules as misidentified products of non-impact related processes. Sedimentary iron- and silica-rich spherules can form by meteoritic ablation, sudden cooling of molten terrestrial eject from an extraterrestrial (ET) impact (4), volcanism, industrial processes, or slow biological and physical processes.