A Superflare and Geomagnetic Excursion as the Triggers for the Younger Dryas Climatic Event and Terminal Pleistocene Extinctions

The onset of the Younger Dryas (YD) stadial at ~12,850 cal. yr BP remains one of the most abrupt climatic transitions in the geologic record, coinciding with megafaunal extinctions and human cultural shifts. The Younger Dryas Impact Hypothesis (YDIH) proposes a cosmic event but struggles to explain the absence of a crater, terrestrial isotopic signatures of key proxies, and the hemispheric bias of cooling. We propose an alternative, comprehensive mechanism: a solar superflare, occurring during the Gothenburg geomagnetic excursion, which dramatically weakened Earth's magnetosphere. This event induced a hemispheric-scale lightning superstorm, igniting atmospheric methane and terrestrial biomass. This led to a cascade of effects: the production of nitrogen oxides (NOₓ) and ozone depletion; the formation of nanodiamonds (including lonsdaleite) via plasma deposition; the mobilization of terrestrial platinum and microspherules; and the injection of massive quantities of combustion aerosols into the atmosphere. The subsequent climatic feedbacks—including ice-sheet destabilization, ocean circulation changes, and UV stress—provide a parsimonious explanation for the YD onset, the extinction event, and the full suite of geochemical proxies recorded in ice cores and terrestrial sediments, without invoking an extraterrestrial impact.