[M-IS18] Paleoclimatology and paleoceanography

[MIS18-28] Impact-related Phanerozoic extinctions driven by soot aerosol production in hydrocarbon-rich target rocks

*Kaiho Kunio¹, Naga Oshima² (1.Tohoku University, 2.Meteorological Research Institute)

Keywords:Asteroid/comet impact, Climate change, Extinction, Soot aerosols, Sulfuric acid aerosols

Comets and asteroids have struck the Earth many times in the Phanerozoic Eon, most notably at the end of the Cretaceous Period. While the three largest impact events coincided with global extinction, most impacts had little effect on extinction events. A consistent mechanism linking impact size, environmental change, and extinction magnitude has not yet been identified. Here we demonstrate that soot aerosol formation during ignition of hydrocarbons in sedimentary target rocks by impacts is the critical factor explaining the variability in biotic responses. Impact-derived hydrocarbon soot has a greater influence on global extinctions than other impact-generated aerosols, including sulfuric acid, wildfire soot, and dust aerosols. Among impact-associated Phanerozoic extinctions, we find a direct relationship between hydrocarbon soot production, global cooling, extinction magnitude, and frequency of mass extinctions. The degree of impact-generated cooling largely depends on the amount of buried hydrocarbon in target rocks, which was originally sourced from organisms and contingent on geologic and biological history. The impact target sensitivity induces large variations in climate response, ranging from negligible climate change with no associated extinctions to significant global climate change, potentially even greater than that leading to the extinction of nonavian dinosaurs. Small variations in composition of impact sites can result in different biotic responses. Previous life originates hydrocarbon that may later act as the trigger for impact-generated global cooling and future extinctions. The cause of impact-related extinctions is intrinsic.