Comets do not need to be dinosaur-killers to change the course of human history, according to the Holocene Impact Working Group, whose research anchors this episode of The Universe. The group argues that smaller impacts, the kind that leave no obvious crater and get overlooked by mainstream geology, hit Earth more often than assumed and still carry enough force to reshape civilizations. The film tests that idea against specific events: flood myths that recur across unrelated cultures and may preserve memory of real inundations, a global cooling episode in 535 A.D. that dimmed the sun and disrupted harvests across continents, and the sudden disappearance of the Clovis people from North America roughly 12,900 years ago. Researchers walk through the physical evidence they use to argue for impact rather than coincidence, including sediment layers and the mismatch between how often big comets should hit and how often catastrophes actually occur in the historical and archaeological record. The case stays speculative throughout, offered as a working hypothesis rather than a settled finding.