^This^
Here's the the thing, it doesn't matter how impermenant or how old, we ALWAYS find evidence. They've found fossils from the dawn of life, we've found human remains more than 100,000 years old. Are you really telling me that an advanced civilization arose and fell and we don't have any credible shred of evidence? Think of how many books the human race has written and how many ways it's been stored, on everything from cunifom tablets to optical disc. You are telling me that if we bit the big one tomorrow none of that would last the eons? Even ignoring that, advanced civilizations work on the human body via surgery and artifical limb/organ replacement, and titanium screws and plates last a hell of a long time. So how come we haven't found any? Also an advancement of civilization always equates to a population boom. We would find a ton of human fossils from any period of a suitably advanced civilization but we havent' found that. The global population has been steadly increasing since the dawn of man as technology and the average life expectancy has increased. Long story short, no evidence = it didn't happen. This applies to all the crackpot science as well.... bigfoot, alien abduction, the Lochness monster, ect.
I can't believe I'm having to explain this to a fully grown adult.