The problem is we have no way to test this, since >4.5 Gyr of tectonic activity on Earth have erased essentially all evidence from this time. #Exoplanets to the rescue! 😀 Hydrogen-rich atmosphere have large scale heights, so if such reduced post-impact atmospheres would be common, we should see it with exoplanet telescopes like #JWST, and possibly with #Ariel. Attached a figure from Rimmer+2019, showing potential ethylene and acetylene features in a post-impact atmosphere.
If we want to do this, we need to look at M star exoplanets, because there are only a handful of G star exoplanets around, but they are too old. We want to look at *young* planets/systems. Figure from Timothy Gebhard (Tübingen/ETHZ).