There are various possibilities. Before writing developed, history was all oral, which means the story gets changed little by little, over time and as tribes migrate/commingle the information slowly disseminates. The last glacial maximum was around 20,000 years ago and humans were certainly around to witness flooding the likes of which we have a hard time even comprehending.
The huge Glacial lakes would break open multiple times and repeatedly flood the land. The area south of the glacier over Chicago has evidence of at least 5 floods, that may have occurred over the course of over 100 years (Kankakee Torrent).
In Europe, the Alps may have been covered with a huge Ice Sheet too:
The obligatory lecture on what glacial lakes did in Washington State (courtesy of
Siddar
in the Geology thread):
I really enjoyed that video (skipped some stuff I already knew, but his points are solid). There is another video thats not by crackpots, going over the asteroid that hit in that area that has subsequent hits around it, and spreading all the way to the east coast and possibly into the Atlantic Ocean. Ive been to a few and never even thought about why they were just big ass circles/ovals.
The realistic opinions of what people "think" could have been are just interesting altogether. Theyve found glacier evidence in North Africa, the last place in MY mind that a Glacier would have been, 58,000+ years ago (
1). Then, you can just do a basic google of the
oldest known fossils of Humans, and human-like creatures - which these things are so fucking old, we dont know shit about what they were like, what they did, or anything similar and all you end up reading about is a bunch of assumptions. Clearly the assumptions are based on what scientist "think" they could achieve based on brain size, and other similar characteristics - but its not like we have real world proof. Much less, if we account for the newer, modern human, remains - they date back 40k years ago - and.. really, if someone is even remotely close to what your average IQ worldwide is, today, who is to say they couldnt have achieved much in the way of written language, some of which dates back to
12,000 years ago. Not really an "ANCIENT ALIENS" kind of conversation - but I just feel like we dont really know shit and we wont ever know more than a basic amount because after a certain time period, actual evidence has just been completely erased to time.
But my point is, I dont think anyone can say for certain what people actually went through in the distant past that would create most of the stories that we hear, across cultures that are on distant sides of the world. How a pre-existing tribe in Australia (no contact w/whitey) came to have an eerily similar story about the Seven Sisters (stars) that ancient Europeans civilizations had is just awe inspiring by itself.