Comprehensive refutation of the Younger Dryas Impact Hypothesis (YDIH)

Abstract

A series of publications purport to provide evidence that the Earth was subjected to an extraterrestrial event or events at ∼12.9 ka creating an environmental cataclysm and the onset of the Younger Dryas stadial. The varied and sometime conflicting speculations in those publications have become known collectively as the “Younger Dryas Impact Hypothesis” (YDIH). As the YDIH has evolved, it has yet to converge into a hypothesis with a self-consistent scenario involving orbital dynamics, impact physics, geology, geochemistry, paleobotany, paleoclimatology, and anthropology. The YDIH invokes a cosmic event at a moment in time to explain complex processes that varied in space and time around the globe. No craters have been identified that date to the onset of the Younger Dryas. The physical evidence offered in support of an impact is nano to microscopic in scale, e.g., charcoal, carbon spherules, magnetic grains/spherules, nanodiamonds, and Pt minerals to name a few. However, many have critical issues with their identification, measurement, and interpretation. Furthermore, most are associated with terrestrial processes not uniquely associated with impacts or periods of abrupt climate change. Very few sites with high levels of any of the purported indicators have accurate and high-precision dating to 12.9 ka. The identification and quantification of several purported impact indicators is also questionable. The claim that a suite of supposed indicators is unique to that moment is not substantiated with data. There is no obvious evidence of environmental cataclysm at that time in the vast published geomorphic or paleobotanical records. There is no support for the basic premise of the YDIH that human populations were diminished, and individual species of late Pleistocene megafauna became extinct or were diminished due to catastrophe. Evidence and arguments purported to support the YDIH involve flawed methodologies, inappropriate assumptions, questionable conclusions, misstatements of fact, misleading information, unsupported claims, irreproducible observations, logical fallacies, and selected omission of contrary information. In this comprehensive review of the available evidence, we address and draw attention to these critical failings. We demonstrate that research in numerous fields has shown the YDIH should be rejected.