I don't know why I didn't notice this thread until today, but this is right down my alley.
I'm currently reading Andrew Collin's book on Gobekli Tepe, which I find quite interesting. I'm a big fan of the ancient "advanced" civilisation theory. I've mentioned this before in other threads, but will surmise here.
I think people underestimate the fragility of "advance" civilisations. Rome, for example, was amazingly advanced in many areas. However, with the collapse of the West Roman Empire, and the ensuing 1000 year Dark Ages, we almost lost a huge amount of that cumulative information. Ironically, had it not been for the dedication of monks preserving and translating ancient manuscripts (monks part of a system that helped destroy the empire and suppress knowledge in the first place), then the re-learning of this information during the Renaissance could have been a much longer and more painful task.
The main problem with this lost civilisation theory has now been solved, in my mind, with all the research into the comet/asteroid cataclysm during the Younger Dryads or whatever it's called about 12 thousand years ago. Not only would such an event cause mass extinctions, crop failures and starvation, but the climate change and resulting ice age and re-thawing would devastate coastlines, which are usually the main centers of population. Therefore, as some have speculated, a lot of the lost evidence may be hiding both beneath the waves, but also beneath the sea bed.
It would also help to explain a lot of the ancient fascination with the stars and sky. Sure, the sun and the moon, as well as the night sky are pretty fascinating in and off themselves, but if there was a long memory of cataclysm coming from there, then it might help explain the dedication to research into the skies so long ago, that can be revealed in ancient knowledge of such long term events as Procession of the Equinoxes.
A lot of shared technology, as well as study in cultivated plant distributions seem to also suggest contact between different continents, including contact between the Americas and Eurasia, in the distant past.
Now, I don't think any past civilisation managed to reach a level of technological sophistication that we have. But I do think they could have managed to have gained a level of technology at least as good as the Romans or ancient Chinese, possibly surpassing them in certain fields. It also wouldn't surprise me if this cataclysm has left some permanent mark or "scar" on our collective consciousness or even DNA. By that I mean when a cataclysm hits, and survival becomes very difficult, then there is a good chance that people with certain traits that perhaps were not very common among the main stream population pre-cataclysm, might survive better than the others, thereby permanently changing the characteristics of the Human Race.
I think this is a field that has been fringe for a long time, but is now slowly gaining more attention, and prominence, thanks in part to research done in recent decades, and stunning archaeological finds such as Gobekli Tepe. The future is therefore bright for those of us who are interested in this stuff. And you don't need to add anything spooky, such as Aliens, into the mix to realise how fascinating this all is!
