Earlier quoted context omitted.
It is. I wish the conspiracy theorist 'the pyramids could not have been built by humans' etc etc crowds didn't exist, because I wish there was space to theorise about pre-human, pre-ape intelligent culture just for fun. Same with UFOs. It seems to have changed in the past few years, but for a long time interest in them was associated with wackiness, and it was not something you could really discuss with a genuine sen…
That ol' Silurian Hypothesis is fun, but, knowing how damn smart birds are, it's not inconceivable that the theropods could have become advanced enough to be at least tool-users. Of course, now, we know they probably had as much similarity to lizards as we do. Another interesting thought experiment is an octopus civilization. They are probably smart enough to have also developed along those lines. Depending on what t…
It depends who comes searching. u235 has a half-life of ~700m years, so finding it in enough places (i.e. rocket silos, even if underground) and obviously processed into spheres, would raise some advanced alien eyebrows. There's also a chance that some things we left on the Moon / in high orbits will survive for a few million years. (also the test tubes on Mars and the rovers themselves, some have RTGs which, even if "depleted" of usable energy might still register as artificial)