Younger Dryas Boundary evidence supports fragmented comet airburst hypothesis

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Key facts

• The Younger Dryas impact hypothesis was proposed in 2007 by Firestone, West, Kennett, and the speaker, positing a fragmented comet encounter around 12,800 years ago
• The hypothesis proposes the largest event was an airburst or touchdown impact over the Laurentide Ice Sheet, which was up to 2 km thick near the Great Lakes
• No crater is required because a low-density comet fragment hitting 2 km of ice would vaporize and melt rather than reach bedrock
• Physical evidence found at more than 50 sites across North America, Europe, the Middle East, and Africa in a thin layer dated to ~12,800 years ago
• Key sites include Abu Hureyra (Syria), Murray Springs (Arizona), Blackwater Draw (New Mexico), Topper (South Carolina), and Wonder Crater (South Africa)
• YDB layer markers include nanodiamonds, magnetic and glassy microspherules, and shock-fractured quartz matching the diagnostic standard used to confirm the Ries impact crater in Germany
• A platinum spike was first identified in the Greenland GISP2 ice core and later reported on five continents
• The YDB layer sits beneath the black mat, a dark algal-rich sediment marking a shift to wet, marshy conditions
• In 2025, the Comet Research Group investigated the Perkins Plume site in Louisiana, argued to preserve geological evidence of an airburst plume
• Critics Holliday and Van Hessel's team note that Laurentide moraines around the Great Lakes show no evidence of sudden catastrophic disruption

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