According to physics simulations, the atmosphere was composed of vaporised rock for several centuries after the impact until it cooled down below 1000 degrees.

According to physics simulations, the atmosphere was composed of vaporised rock for several centuries after the impact until it cooled down below 1000 degrees. The entire surface was magma. https://en.wikipedia.org/wiki/Synestia https://en.wikipedia.org/wiki/Synestia