Uhm, I would say that we actually know quite a bit about the history of our planet, and one thing abundantly missing is traces of any former civilizations living here. And given that we are talking about a highly advanced race with the capability for interstellar space travel, they should have left behind a bunch of artifacts. Unless they, now that they were faced with an extinction level event in the form of an asteroid, decided to thoroughly clean up before they left and bring everything with them. Somehow that doesn't really sound like the smartest thing to do.
And I certainly wouldn't call our knowledge tales - that might offend a bunch of biologists/anthropologists/geologist/etc.
Offend away, LOL all we know about is what we have found which isnt much, lets face it the Sumerians got there knowledge from somewhere they didnt just come into being knowing all they know even they say in there writings that they were given the info but of course we discount this because it doesnt fit in with our pre conceived notions. We know very little but think we know everything which is why it takes so long for us to learn anything. When you think you know everything you arent looking for answers anymore just a way to back up what you think to be correct. We have theories not much more. I think our scientists are to closed minded to find anything new. I also think that if a civilization was here a 100,000 years or more ago we wouldnt be able to find anything it would have been long covered up by our own earth tectonics buried beneath tons of earth or just flat destroyed. We find a few animals but it is pure dumb luck. Nobody thought Troy was real but what we found it imagine that. I also love the way that scientist decide what other civilizations were thinking when we have no way of knowing.