Hypervelocity impacts on anhydrite (CaSO
4) induce degassing of SO
2. Degassed SO
2 is released into the atmosphere of planets and is thought to play an important role in controlling the surface environment of planets. For example, sulfate aerosols produced from SO
2 were thought to block the sunlight and invoke the mass extinction at 65 Ma Cretaceous/Tertiary boundary (K/T boundary). However, it is suggested that these SO
2 back-reacts with CaO into CaSO
4 (i.e., SO
2+1/2O
2+CaO->CaSO
4) in impact-induced vapor clouds soon after degassing. In this case, the amount of SO
2 released into the atmosphere decreases.
Impact-induced vapor clouds larger than the atmospheric scale height cool by adiabatic expansion and reach the temperature-pressure state where the back-reaction of SO
2 and CaO is thermodynamically possible. However, if the reaction rate is slower than the cooling rate of vapor clouds, the back-reaction is inhibited kinetically.
In this study we determine the reaction rate of the back-reaction SO
2+1/2O
2+CaO->CaSO
4. Then, we compare the reaction rate and the cooling rate of the impact-induced vapor clouds to examine whether the back-reaction really occur. The results show that the back-reaction occurs in K/T-scale vapor clouds and that more than 40% of SO
2 are consumed.
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