Comment by jerf

I'm not to stuck on the complete, 100% impossibility of things to be found.

But one counterargument that can be made is that fossilization requires very specific circumstances, and the legacy of the dinosaurs is from millions of years of opportunities. A blip of a 500 year civilization might not leave much behind.

No, I wouldn't expect a big pile of iron to leave anything interesting behind. It would rust, and rust has no structurally integrity and probably wouldn't resist the general forces of time very well. On geological timeframes rust is soluable in water.

However, I couldn't tell you that about every last industrial artifact we have. Could the Hoover Dam still indicate some sort of obvious construction activity a few million years hence? Could some of the concrete end up preserved and some future civilization realize that it is too precisely formulated for an engineering purpose to be constructed? Could some titanium structure survive for extended periods of time even though everything else in the plane or whatever else is long gone? Could New Orleans end up sinking into muck and leave some sort of fossilization behind of things that are still clearly artifacts millions of years later? It's hard to prove that every last thing we create has absolutely no chance of being recognizable as an artifact even in millions of years.

Especially if we leave Earth and start including the moon. Just a few things here or there could be wiped out with an unlucky asteroid strike, but if something was really systematically up there for long periods of time doing intelligent things, even hundreds of millions of years ago, could still leave an obviously-intelligent footprint.