alt Hacker News> The simple answer is that some storied reference events that happened that long ago.
This is another thing that you can't know.
If there is a match between an inferred geological event and a mythological event, you'd still have to ask "what is the rate of this happening by coincidence?"
And then you'd still have to ask yourself, whether anything is real or a simulation, or a dream of god, etc.
Otherwise history is indeed much guesswork, as we don't have a timemachine and rely on lot's of indirect evidence for everything.