[jerf]

I think we'd be able to find a previous civilization of our current technological advancement by finding a lot of veins of mineral resources mined out, except for the trailings around the edges. I've never heard even a whisper of such a mineral formation being found, and with the amount of money such mineral industrial research accounts for, I suspect by now we would have found such a thing if it exists, especially if it existed in quantity.

There may be no structures or artifacts that survived 65 millions years, but there's plenty of holes that would have, in natural structures that to all appearances are older than 65 million years, should have been about as available then as they are now, and are obviously undisturbed.

[nostrademons]

What if they used different minerals because before they mined them out, different minerals were present? To what extent is our dependence on iron, copper, and bronze a historical accident because that's what was available to our ancestors, and to what extent might we have used different metals if easily-extractable ores for them were present?

Despite being the third most common element in the earth's crust, aluminum cost more than gold and was rarely used for industrial purposes before the Hall-Heroult process for smelting it from alumina and the Bayer process for smelting it from Bauxite.

Rare-earths display a similar profile: they are abundant in the earth's crust, but not in any form that we can easily mine and extract. What if a past dinosaur civilization mined out all the easy rare-earth deposits building iPhones and batteries?

[jerf]

"What if they used different minerals because before they mined them out, different minerals were present?"

I'd point out I didn't say that all the minerals were gone, but that the good veins were gone, surrounded by the stuff they left behind. I say that because that's how we do it now, and we do it for economic reasons that any civilization will be subject to. This is a particular pattern that I'm not aware of anyone ever observing.

I am also not aware of anyone even proposing anomalies in element distribution of things like rare earths. Rare earths aren't as rare as their name suggests as I'm sure you know, but as you go up the periodic table, you do naturally get less of them in the crust for several reasons (less created in the supernovas that created the heavy elements, and more of it sinking in the earth during the early phase). It's possible that our understanding of elemental distribution is a "just so" story created by what turns out to be artificial manipulation of the contents in the past, but given that our understanding of the processes that led to the current distribution includes a lot of astronomical observations, it'd be one heck of a "just so" story at this point. I am not aware of even a hint of an observation that requires an intelligent civilization on Earth in the past.

I'd say if you really want to have some fun, hypothesize a dinosaur civilization that attained some sort of singularity, and on the way out chose to leave behind machines that restored Earth to its "natural" state over the course of a few centuries or something, thus wiping out all traces of their presence to make way for the next civilization. It's not impossible to imagine a human singularity ending that way. Come up with some semi-compelling reason why all or at least most civilizations would tend to do that and you've got a fun premise for a sci-fi story universe. Perhaps we're not merely the second, but the dozenth. Heck, maybe we're not even the first primate.

(Another bonus "thing we clearly don't see": At the current rate of human advancement, in another couple hundred to couple thousand years, even putting aside really high-end nanotech, our primary contribution to the history of planet Earth may not be the sudden extinction of a lot of life forms, but the sudden proliferation of a lot of life forms, along with visible cross-transfer of genetic characteristics that couldn't possibly have naturally occurred. Even if the intelligent civilization completely keeled over dead, or Transcended, or whatever, the mark on the planet's genetic history would be visible quite possibly right up to the point the Sun sterilizes the Earth. We aren't there yet, but we are darned close. As much fun as a lot of people seem to derive from wringing their hands and posturing about how terrible humanity is, on a geological time scale, we may not be living in an Athropocene Extinction, but instead in the gestational phase of the Anthropocene Explosion.)

[ncmncm]

Of all of the above, the existence of holes seem to be the only compelling traces.

[jerf]

I mention it because it's the earliest one I can think of in our technological development. If we continue advancing, we will eventually get to that genetic diversification bit, but it seems that happens after you get the point where you can wipe out your own civilization with nukes, so that one is much less reliable.

(The Singularity paragraph is just for fun. Almost by definition, there is no reasonable way to ever collect evidence for it.)