Direct measurements of chemical composition of shock-induced gases from calcite: an intense global warming after the Chicxulub impact due to the indirect greenhouse effect of carbon monoxide

Shock-induced devolatilization in hypervelocity impacts has been considered to play important roles in the atmospheric evolution and mass extinctions in Earthʹs history. Although the chemical composition of shock-induced gas species from carbonate rocks has been considered as a key to understand the environmental change after the Chicxulub impact, it has not been investigated extensively before. Here, we conduct direct measurements of the chemical composition (CO/CO2) of shock-induced gas species from calcite (CaCO3) using both a laser gun system and an isotopic labeling technique. The CO/CO2 ratio of the shock-induced gas species from calcite is measured to be 2.02 ± 0.41, suggesting that gaseous CO has been dominant in the shock-induced gases in the Chicxulub impact. In order to evaluate the environmental effects of the injection of CO gas, we investigated the post-impact atmospheric chemistry by incorporating our experimental results into a tropospheric photochemical model. The results suggest that an intense (2–5 °C) global warming would have lasted for several years after a Chicxulub-size impact mainly due to the greenhouse effect of tropospheric O3, which is produced via photochemical reactions associated with CO gas. Such an intense global warming could have damaged the biosphere in the mass extinction at the Cretaceous–Paleogene (K–P) boundary.