I went to my other computer and watched the end. Wow I like their theories a lot it seems to make most sense. It seems like our civilization just happens to be the one that exists now, and the other civilizations must have gone to equal or greater lengths in terms of technology and then suddenly wiped out by disaster, be it natural disaster or caused by extra terrestrials.

As in, what if our civilization are entirely not the descend of the Mayans, Egyptians and whoever else that built those humongous structures and had the advanced technologies and our civilization back then simply didn't know they existed?

The aliens theory were thoroughly possible too, they might have come, done things, and brought the party van and got those people out of here with them...and then we came along. This theory is so mind blasting!