Firestone et al.'s 2007 PNAS paper reported a suite of markers at the Younger Dryas boundary, magnetic microspherules, carbon spherules, meltglass, charcoal, platinum-group anomalies, and nanodiamonds including lonsdaleite-like crystals, arguing no single proxy was decisive but their co-occurrence in one narrow horizon pointed to an extraterrestrial event. Kinzie et al. (2014) tallied the suite across sites on multiple continents.
The folk saga: Surovell et al. (2009) failed to reproduce the markers at key sites; Daulton argued the diamonds were misidentified graphene aggregates; then Wittke, Kinzie, and LeCompte reported replications; Tian et al.'s isotopes argued against a mantle origin; Holliday et al.'s 2023 review declared the evidence weak, and a 2026 rebuttal accused that review of systematic misrepresentation. Each side claims the other misreads the dirt.
The claim: shock diamonds are nature's notary, forgeable by nothing short of cosmic violence, and their presence at the exact boundary, alongside platinum spikes in Greenland ice, closes the case the crater never could. Skeptics answer that cosmic dust rains nanodiamonds constantly and background contamination is unkillable.
Are the nanodiamonds the smoking gun, or the Rorschach test of the whole impact debate?