A global charcoal and soot layer, coinciding with the Ir layer, is present at the Cretaceous/Tertiary (K/T) boundary, and apparently comes from a global fire. Soot is present even in the basal layer of the boundary clay, implying that the fire started soon after the impact. No comparable soot enrichments, let alone of global extent, occur in the latest Maastrichtian or in a wide range of other marine sediments.

Much or all of the fuel was biomass, as indicated by the presence of retene (a hydrocarbon diagnostic of resinous wood fires) and by the carbon isotopic composition (δ¹³C...