Been thinking along the lines of Planet of the Apes -but without any man made catastrophe, meteorite impact and climate stabilization- what sort of structures or evidence of our civilization would remain in five or six million years if we all just vanish? Would an intelligent species of evolved insects -or something else- find buried artifacts in the ground like we did the dinosaurs? Would ancient structures like the pyramids or Great Wall remain for that long, and would any modern things like the Eiffel tower, Burj Khalifa, or even some present day Doomsday Vaults survive that amount of time? In our digitized age, I assume that not much would remain, other than satellites maybe or I suppose any modern species that just happens to get preserved like a dinosaur did.
At least for our civiliſation, there would always be the echoes of ſignals like the Aracebo Meſſage that would be around for future civiliſations to catch regardleſs of what happened here on Earth.
It’s still a matter of timescale, as in “how far future are we talking?”. On a stellar scale, they’d need to get here in the next billion years or so before the expansion of the sun boils off everything above the lithosphere. On a geological scale, it’s only a couple hundred million years 'til everything that isn’t already buried or washed into the sea is getting squashed into a new pangea. On a climatological scale, corrosion and decay/overgrowth will render almost all artifacts unrecognizable within a couple of thousand years, though it’d be a few tens of thousands before our impact on the atmosphere is nulled. On a human timescale, the inverse-square law means that our radio signals are only detectable without astronomically-sized antennas within a shell of a few dozen light years or so.