Not people. Dinosaurs, intelligent crocodiles, industrialised trilobites, whatever it might be. So many millions of years ago that there may be no such thing as permanent marks.

You possibly could be thinking about an Atlantis type of scenario, the idea that relatively advanced prehistoric human civilisations could have risen say 100,000 years ago and fallen without a trace (especially if they literally fell into the sea). Which does have some level of possibility, but indeed there isn't much chance they could have developed advanced sciences.

The thing is, though it seems far wackier, it's interesting to think that there literally could have been populations of millions of intelligent lizards (or whatever) for hundreds of thousands of years, and for the fossil record not to reflect it. It would be amazing if one day a cliff collapsed and we found an intact fossilised dinosaur airliner or whatever, but this article is about whether less direct evidence of such a civilisation, if it ever existed, would persist.