EXTRATERRESTRIAL AND TERRESTRIAL SIGNATURES AT THE ONSET OF THE YOUNGER DRYAS

The recent suggestion of a catastrophic impact event at 12,900 calibrated years before present (cal BP) has been invoked as triggering the North American megafaunal extinction, demise of Clovis Paleoindians, and the Younger Dryas (YD) paleoclimatic reversal. This hypothesized impact event has received energetic reactions, ranging from public excitement to intense skepticism. Our group – and others working separately – have attempted to reproduce and test markers presented as evidence of this YD extraterrestrial event.

Accepted signatures of earth impact events include craters, meteorite fragments, shatter cones, shocked and high pressure minerals, planar deformation features, tektite fields, diaplectic glass, etc. None of these has been documented in the case of the YD event. Instead new or suspect signatures have been reported, including fullerenes enriched in 3He, metallic grains, soot from impact ignition of global wildfires, spotty “nugget”-type iridium enrichment, microspherules, carbon spherular forms and “elongates,” and most recently nanodiamonds and other diamond forms.

We have sampled sedimentary sections in California and Arizona, including two of the same sections analyzed by the YD impact group, and analyzed samples for metallic grains, spherules, carbon spherules and elongates, and nanodiamonds. We tested these signatures at the 12,900 cal BP layer as well as multiple horizons above and below. Results generally fall into three categories: 1) signatures that were impossible to reproduce even from the same sections and horizons, 2) terrestrial signatures that were incorrectly identified as extraterrestrial in origin, and 3) true extraterrestrial materials that were ubiquitous through the record, although locally concentrated by sedimentary processes. Many of the purportedly unique markers at the YD boundary layer were found in most or all other sites and horizons analyzed, often at concentrations much higher than at the YD layer itself.