The Younger Dryas Impact Hypothesis (YDIH) proposes that a comet or asteroid struck Earth around 12,900 years ago, triggering the sudden Younger Dryas cooling period and potentially resetting early civilizations. Per Wikipedia, the scientific consensus rejects this as the primary cause—favoring freshwater disruption to ocean circulation instead—but recent research argues the hypothesis was prematurely dismissed and deserves serious reconsideration given supporting evidence like impact glass microspherules in geological cores. It's a classic case of a fringe theory that might have more merit than the establishment initially granted.