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

摘要

Shock-induced devolatilization in hypervelocity impacts has been considered to play important roles in the atmospheric evolution and mass extinctions in Earth's 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 degrees C) global warming would have lasted for several years after a Chicxulub-size impact mainly due to the greenhouse effect of tropospheric O-3, 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.