[B-CG05] 地球史解読：冥王代から現代まで

[BCG05-18] 主要大量絶滅における気候変動の起動メカニズム

*海保 邦夫¹ (1.東北大学)

キーワード：大量絶滅、気候変動、火山活動、小惑星衝突、ガス放出

Major mass extinctions in the Phanerozoic Eon occurred during abrupt global climate changes accompanied by environmental destruction driven by large volcanic eruptions and projectile impacts. Three mass extinctions at the end-Ordovician, Late Devonian, and end-Permian were accompanied by global warming, and two mass extinctions at the end-Triassic and Cretaceous–Paleogene boundary were accompanied by global cooling. However, the mechanism causing the different climatic results is unknown. Here I propose a hypothesis that temperature of magmas intruded to sedimentary rocks controlled the global climate changes induced major mass extinctions. We found high concentration of coronene, which requires extremely high temperature to form from organic matter and hydrocarbons, in sedimentary rocks recording the three major mass extinctions marked by volcanism-induced mass-extinctions and impact-induced global cooling at the Cretaceous–Paleogene boundary. Low coronene concentration was found at the volcanic global cooling at the end-Triassic mass extinction (Kaiho et al., 2022, EPSL). Our heating experiments of typical carbonate and mudstone materials show that relatively low temperature heating (>350 °C) by sills releases massive amounts of SO₂ on a 100 y time scale, whereas higher temperature heating (500–600 °C) forms more CO₂ on the same time scale (Kaiho et al., 2022, EPSL). The combination of our coronene data and laboratory results implies that low heating by sills caused SO₂-dominated gas emission to the stratosphere and low CO₂ emission, inducing global cooling that could have precipitated the end-Triassic mass extinction. The other three volcanic induced mass extinctions accompanied with global warming may have been due to high-temperature volcanism (plume volcanism) forming massive CO₂ emission. High energy of asteroid impact at the Cretaceous–Paleogene boundary caused highest coronene concentration, reading to formation of soot and sulfuric acid aerosols from target rocks, causing global cooling.