biostudies-literatureUnknown110(23)Wittke JHAirbursts/impacts by a fragmented comet or asteroid have been proposed at the Younger Dryas onset (12.80 ± 0.15 ka) based on identification of an assemblage of impact-related proxies, including microspherules, nanodiamonds, and iridium. Distributed across four continents at the Younger Dryas boundary (YDB), spherule peaks have been independently confirmed in eight studies, but unconfirmed in two others, resulting in continued dispute about their occurrence, distribution, and origin. To further address this dispute and better identify YDB spherules, we present results from one of the largest spherule investigations ever undertaken regarding spherule geochemistry, morphologies, origins, and processes of formation. We investigated 18 sites across North America, Europe, and the Middle East, peProceedings of the National Academy of Sciences of the United States of AmericaE2088-97https://www.ebi.ac.uk/biostudies/studies/S-EPMC3677428biostudies-literatureEvidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago.PMC3677428Moore AMBischoff JLMoore CRIsrade-Alcantara IWest ABunch TELipo CPFirestone RBHoward GAKimbel DRHillman GCNabelek LDeCarli PSSakai SWittke JHFerraro DHermes RERay JHDaniel IRRevay ZKletetschka GLopinot NHGoodyear ACTankersley KBKloosterman JBWeaver JCKennett JPKennett DJfalseEvidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago.Airbursts/impacts by a fragmented comet or asteroid have been proposed at the Younger Dryas onset (12.80 ± 0.15 ka) based on identification of an assemblage of impact-related proxies, including microspherules, nanodiamonds, and iridium. Distributed across four continents at the Younger Dryas boundary (YDB), spherule peaks have been independently confirmed in eight studies, but unconfirmed in two others, resulting in continued dispute about their occurrence, distribution, and origin. To further address this dispute and better identify YDB spherules, we present results from one of the largest spherule investigations ever undertaken regarding spherule geochemistry, morphologies, origins, and processes of formation. We investigated 18 sites across North America, Europe, and the Middle East, pe2013-01-01T00:00:00Z2013 Jun2026-05-05T07:45:03.707Z2026-04-07T21:30:08.669ZS-EPMC36774282369061110.1073/pnas.1301760110