Comment by motoboi

We certainly cannot know if a previous intelligent civilization was present on earth before the impact.

And is not even that the impact erased their trace from earth, is that if they got extinct long enough (more than 100 million years ago), with today's technology, we cannot infer their presence, given the fossil (and other types of) record.

A great write up about this is: https://archive.is/https://pacificklaus.com/the-silurian-hyp...