[B-PT27_28AM2] 顕生代生物多様性の変遷：絶滅と多様化

[BPT27-01] 天体衝突が引き起こす海洋酸性化とK/Pg事件の絶滅機構

*大野 宗祐¹、門野 敏彦²、黒澤 耕介¹、羽村 太雅³、境家 達弘⁴、重森 啓介⁴、弘中 陽一郎⁴、佐野 孝好⁴、渡利 威士⁴、大谷 一人⁵、松井 孝典¹、杉田 精司³ (1.千葉工業大学惑星探査研究センター、2.産業医科大学医学部、3.東京大学、4.大阪大学、5.Institut national de la recherche scientifique)

キーワード：K/Pg生物大量絶滅, 天体衝突, 室内実験, 酸性雨, 海洋酸性化, 質量分析

The Cretaceous?Paleogene (K?Pg) mass extinction event at 65.5 Ma triggered by a meteorite impact is one of the most drastic events in the history of life on the Earth. Many hypotheses have been proposed as killing mechanisms induced by the impact, including global darkness due to high concentrations of atmospheric silicate dust particles, global wildfires, greenhouse warming due to CO2 release, and global acid rain. However, the actual mechanism of extinction remains highly controversial. One of the most important clues for understanding the extinction mechanism is the marine plankton record, which indicates that plankton foraminifera, living in the near-surface ocean, suffered very severe extinction in contrast to the high survival ratio of benthic foraminifera. No proposed extinction mechanism can account for this globally observed marine extinction pattern. Here, we show that SO3-rich impact vapor was released in the K-Pg impact and resulted in the occurrence of global acid rain and sudden severe ocean acidification at the end of the Cretaceous, based on the new results of impact experiments at velocities much higher than previous works (> 10 km/s) and theoretical calculations on aerosol coagulation processes. Sudden severe ocean acidification can account for many of the features of various geologic records at the K?Pg boundary, including severe extinction of plankton foraminifera. This extinction mechanism requires impact degassing of SO3-rich vapor, which is not necessarily found at impact sites other than Chicxulub, suggesting that the degree of mass extinction was controlled greatly by target lithology.