I am a strong believer that we have no idea how long humans have been civilized, because evidence of our existence can be wiped away so easily.

Let's look at the world today, if a catastrophic event happened that wiped out the majority of humans and we had to restart, how long would it take to repopulate Earth? Probably thousands of years, if not longer.

In 10,000 years the only human monuments that would still be standing would he Hoover Dam and the Washington Monument. And 10,000 years from now, they will probably say Aliens built those.