I'm not sure why but this suggests a theory of sorts. Kinda makes sense though if you think about it. Everything would be buried or burned from the event. The ones living underground would hopefully be able to get out and repopulate. From there we could hope for another 20-30k years and probably returns orbit again and this time makes further damage. With that history is lost and no evidence of the event except for the Earth's crust from the impact and debris. But to visualize that, not sure where to even begin.