Younger Dryas
In 2016, a report on further analysis of Younger Dryas boundary sediments at nine sites found no evidence of an extraterrestrial impact at the Younger Dryas boundary. Also that year, an analysis of nanodiamond evidence failed to uncover lonsdaleite or a spike in nanodiamond concentration at the . Radiocarbon dating, microscopy of paleobotanical samples, and analytical pyrolysis of fluvial sediments "[found] no evidence in Arlington Canyon for an extraterrestrial impact or catastrophic impact-induced fire." Exposed fluvial sequences in Arlington Canyon on Santa Rosa Island "features centrally in the controversial hypothesis of an extra-terrestrial impact at the onset of the Younger Dryas." The nanodiamond evidence was criticized further in 2017.