I used to get into some of this stuff. Even von Daniken is kind of entertaining.. even though he's a kook. At the very least, it's a fun angle for fiction. This was the direction the earliest fantasy writers kind of went with (like Tolkien and Howard), where, unlike D&D, which has newly invented worlds, their stories were about prehistory. That's more intriguing and magical to me. What if our existing civilizations are just rebuilt versions of the old ones, with only a slight resemblance? What if the world was full of knowledge at one point, but all went up in flames like the library of Alexandria? Except, in this case, the library of Alexandria was the whole world. "Know, oh prince, that between the years when the oceans drank Atlantis and the gleaming cities, and the years of the rise of the Sons of Aryas, there was an Age undreamed of, when shining kingdoms lay spread across the world like blue mantles beneath the stars -- Nemedia, Ophir, Brythunia, Hyperborea, Zamora with its dark-haired women and towers of spider-haunted mystery, Zingara with its chivalry, Koth that bordered on the pastoral lands of Shem, Stygia with its shadow-guarded tombs, Hyrkania whose riders wore steel and gold. But the proudest kingdom of the world was Aquilonia, reigning supreme in the dreaming west...." (From "The Phoenix and the Sword, Robert E Howard).