"Polynesian Expansion.
Moana is based on this mystery. Humans spread from Taiwan to Hawaii and every spit of land in between via dead reckoning then all of us a sudden these separate societies that had no means of communicating just stopped for a thousand years AND THEN started back up at the same time.
We have no idea why they ever sailed over the horizon with no plan OR why they stopped exploring in unison for so long. OR WHY THEY RESTARTED AT THE SAME TIME."