Concrete crumbles.
Iron & steel rust.
Bricks break down to powder.
If a non-human civilization existed 20 million years or so ago on Earth, would there be any trace?
What traces?
How could we recognise these traces?
Would we confuse them with natural phenomena?
If a species is truly different from us, like a reptilian or crusteacian one, would we be able to recognise their artifacts?
Could there have been Others here before us? With, say, a Bronze Age level of technology, or better?
If there were, they were losers who couldn’t sustain their civilization or leave any traces of it.
In any event, not worth worrying about.
Not all metal objects rust. Gold, for example, and if I recall, quite a few civilizations valued it. If, say, an iron axeblade rusts, it’s gonna leave a mark or impression of some kind. Same with organic objects, like wood, if left in the proper place. Remember those dinosaur-skin impressions? The actual skin is long gone, but the impressions on the rock are still there. Trust me, there would be traces of even a stone-age civilization before ours.
What about Cyclopeon Stone Structures? Stone tends to have more staying power, it seems, when it comes to buildings things. Of course, it may not stay together, but at least there might be something left.
Depending on the pre-human civilization’s level of technology, might there be traces in the rock layers of industrial pollutants? I mean, there’s a layer of Irridium down at the 65 million year mark, and we all know what left that…
Probably we would have stumbled on at least a few remnants. Say a garbage heap from a small village. Perhaps the remnants of a group of cooking ovens. A rusted out image of a sword sandwiched between some sandstone. Something incongruous somewhere that would spur research in a certain area for a certain time frame. Unless …
I suppose it largely depends on where they lived, how densely populated they were, how long they were around and how far back in time they existed. If they were in a small enough area they could have been wiped out and covered by some enormous eruption or some sort or maybe the land was being eroded slowly and washed into the ocean leaving little chance that anything would be left to find. There are many places they could have been hidden.
But given how rare life seems to be in the universe I would be extremely (and happily) shocked if such a thing were to be found.
I asked a question like this a while back, but I wanted to know how long evidence of our civilisation would last if all humans were wiped out today; seems that plate subduction would be about the only thing that would wipe it all out with any certainty - it would take however long it takes for the entire crust to be recylced (if that will ever happen now).
I assume that you all have heard of the theory that the moon was formed when a large object collided with the Earth, tearing away a big chunk of it that formed our current satellite. I once saw an interview with one of the men who formed the theory. During the interview he said that it was geologically possible that there was life on Earth before the massive collision, but that any life, and any evidence for it would have been completely obliterated from the creation of the moon.
Instead of large structures I’d be more likely to look for things like quarries and such. Mines. Large holes in the earth that fit pretty easily into the ‘permanent’ category.