The Younger Dryas impact hypothesis, also known as Clovis comet hypothesis, posits that the hemisphere-wide debris field of a large, disintegrating asteroid (or comet) struck North America, South America, Europe, and western Asia approximately 12,800 years ago. This event triggered extensive biomass burning, brief impact winter, climate change, and contributed to extinctions of late Pleistocene megafauna. Controversial from the time it was proposed, this hypothesis continues to be contested by those who prefer to attribute the end-Pleistocene reversal in (global) warming entirely to terrestrial causes. Now, University of California, Santa Barbara’s Professor James Kennett and co-authors present further geologic and...