Proposal that a comet or asteroid struck or exploded over the northern hemisphere about 12,900 years ago, triggering the Younger Dryas cold reversal, the collapse of the North American megafauna and the end of the Clovis archaeological horizon. Put forward by Richard Firestone and colleagues in the Proceedings of the National Academy of Sciences in 2007, it rests on claimed impact markers in the boundary layer: magnetic microspherules, nanodiamonds, carbon spherules, and a platinum anomaly reported from Greenland ice in 2013. Independent attempts to reproduce those markers have repeatedly failed or found them in the wrong layers, and critics including Vance Holliday argue that the chronology does not hold across sites. It remains a live minority position in the literature rather than a settled result. Graham Hancock adopted it in Magicians of the Gods (2015) as the replacement for Earth-Crust Displacement, which is a change of mechanism rather than a change of conclusion. Heather Lynn places her displaced population’s origin in a northern catastrophe more than ten thousand years ago, possibly triggered by a meteor, which is the Younger Dryas impact scenario Graham Hancock adopted in 2015, arrived at independently and applied to Mesopotamia rather than to the Americas or Antarctica. The same evidentiary style, and much of the same author list, produced the Tall el-Hammam Airburst Hypothesis of 2021, retracted in April 2025, and two further papers retracted together on 11 February 2026: a Baffin Bay core reporting comet dust, microspherules and a platinum anomaly, and a claim of shocked quartz at the Younger Dryas onset. Most of the authors disagreed with both retractions, and one called the criticism procedural rather than scientific. Three retractions from one author group is a fact about that group’s practice rather than a verdict on the hypothesis.
Where the argument stands
Vance Holliday and colleagues published a comprehensive refutation in Earth-Science Reviews in 2023. The impact side answered in the same journal and in ScienceOpen in 2024 and again in 2026, so the refutation and the counter-refutations are both on the record. The Greenland platinum anomaly has been reread: Green, Baldini and colleagues argued in PLOS One in September 2025 for a possible volcanic origin, on two grounds. The GISP2 platinum peak at 12,822 BP falls roughly 45 to 50 years after the Younger Dryas onset at 12,870 plus or minus 30 BP, and it persists for about fourteen years, which reads more like fissure volcanism than an instantaneous strike. The authors write “suggest” and “possible”. What the sharper time resolution settles is narrower than either side would like: whatever its source, that marker arrives too late to have been the trigger.
An unexpected critic
Robert Schoch gives appendix nine of Origins of the Sphinx to dismantling the hypothesis, which would have handed his own argument a ready-made catastrophe. He writes that “the end of the last ice age does not correspond to the potential strike by a comet or meteorite hypothesized by Firestone et al. (2007), even if such did occur”, and that “personally I am not adverse to an impact hypothesis per se … However, as more researchers have studied the issue, much of the data supporting the impact hypothesis has been questioned”. He raised a volcanic source for the platinum anomaly in 2017, where the 2025 paper arrived eight years later. Neither he nor those authors rule out a small, local impact unrelated to the Younger Dryas.
Connections
Earth-Crust Displacement · Graham Hancock · Ancient Apocalypse · Heather Lynn · Silurian Hypothesis · Tall el-Hammam Airburst Hypothesis · Robert Schoch · Origins of the Sphinx