>A giant, ≥100-km-diameter comet entered an Earth-crossing orbit in the inner solar system and began a cascade of disintegrations (Napier 2010). Nu- merous cometary fragments from the debris stream entered Earth’s atmosphere ∼12,800 y ago and detonated above and/or collided with land, ice sheets, and oceans across at least four continents in the Northern and Southern Hemispheres.