Graham Hancock produced the show....roughly six episodes.
He examines various cultures that lived, and then disappeared....leaving various mystery structures.
So to lay out his opinion.....he believes as the Younger Dryes period (12,900 years ago) started up....that whole bunch of cultures went 'belly-up' (likely a meteor hit). These cultures....if you measured up their use of technology.....were probably at the 1890s level of existence.
In his scenario....only a limited number of this group survived, and they went out into the hunter-gatherer world....providing x-amount of their knowledge.
Archelogy today? They can't really stamp his version correct, and they have a fair number of empty holes....where their 'story' can't fit correctly.
My advice, if you can find the show....watch it. I'm not saying he has a perfect fix for the story he tells, but there's a lot of stuff which really can't be explained.