Part of this is the realization that backward (or forward) tens of millions of years or more is a place as awesomely distant as a star hundreds of light years away. Billions of years may as well be another galaxy. Time as well as space is vast, and we really can't see details very far. There could have been two or three "flowerings" of high intelligence on Earth so far and we would have little direct evidence.
Definitely! I often wonder about the evidence (who knows if the dinosaurs had computers and mechanical flight for a short time(geologically speaking)?) How could we?
[Edited to make it clear I was talking about airplanes]
> Definitely! I often wonder about the evidence (who knows if the dinosaurs had computers and mechanical flight for a short time(geologically speaking)?) How could we?
We've found fossilized dinosaur bones in silted up riverbeds, but no dinosaur-era subway tunnels that silted up with what would now be mudrock. If dinosaurs had computers and mechanical flight, they'd almost undoubtedly have had subways, sewers, and bunkers that we could find at least trace evidence of.
I think a civilization like ours might be hard to miss, but if they only hit e.g. stone age levels we could easily miss that.
Of course it depends on the time scale. An industrial civilization 250mya might leave little traces unless you knew exactly where to look and what to look for.
There is also the hidden assumption that they would build the same sorts of things as us for the same reasons, a form of anthropocentrism.
> I don't know if subways would have fossilized if they were only around for 1000 years, 60-120 million years ago.
I think you misunderstand. The extent and location of the systems would matter more than the duration of their use. What we'd be looking for is the geological result of artificial tunnels filling up with sediment that then undergoes normal geological processes to solidify into rock.
