THE RAIN OF FIRE THAT ENDED THE MESOZOIC: MOLTEN ROCK DROPLETS DURING THE DINOSAUR APOCALYPSE

The Chicxulub asteroid impact (~66 Ma) coincided with the Cretaceous-Paleogene (K-Pg) boundary and was the probable trigger for the last mass extinction in Earth's history. The events unleashed by the collision led to the demise of three-quarters of the species, including the iconic non-avian dinosaurs. During the crater formation, millions of tons of molten and vaporized rock, dust, and gases were expelled into the atmosphere. These materials spread across the globe and fell as a scorching rain that lasted for hours. The soot resulting from the global fires, the dust, and the settling of the finer fraction persisted for weeks or months after impact. Tiny glass droplets (impact spherules) represent a significant volume of the ejecta. Our hypothesis suggests that the morphology, size, and distribution of the impact spherules within the K-Pg bed are related to their origin and transport mechanisms. To test this, thousands of spherules from Wahalak Creek (Mississippi), Gorgonilla Island (Colombia), and Zumaia (Spain) were described, analyzed, and illustrated. Our observations suggest that three fractions within the K-Pg bed are related to three different transport mechanisms: 1) the coarser fraction (lower layer when it has not been reworked) records the accumulation of rotational molten rock droplets, which arrived early at very temperature to locations close to the impact site following ballistic trajectories. 2) the intermediate fraction (middle layer) represents tiny molten rock droplets transported by the rapid expansion of a high-temperature cloud. 3) the finer fraction (upper layer, commonly called the fireball layer) is globally distributed and represents the accumulation of tiny droplets condensed from a vapor cloud. Our results show that Chicxulub's ejecta were distributed through different processes, each leaving a distinctive signature. This information provides valuable insights into ejecta distribution during massive asteroid impacts and enhances our understanding of the Chicxulub event and its aftermath.