Global K-Pg Layer Deposited From a Dust Cloud

Although it is widely agreed that the distal K-Pg clay layer contains ejecta from the Chicxulub impact site, no current models can explain how these ejecta travel from the impact site around the globe. A widely accepted hypothesis is that impact spherules and shocked minerals in the layer were ejected from an expanding impact plume and traveled to their final destination on a ballistic path. Shocked minerals, however, are ejected at too low a velocity to reach distal sites, and plausible ballistic ejection models cannot explain the observed ejecta distribution. Using a suite of numerical simulations, we find that intense interactions between the ejecta curtain and atmosphere generate a fast-moving dust cloud traveling at speeds of a few kilometers per second, which carries a substantial fraction of ejecta, including shocked minerals, to distal sites. We conclude that ejecta curtain material must make a major contribution to the formation of the distal K-Pg layer. Plain Language Summary We first discovered that the Earth had been hit by a large asteroid 66 million years ago when a thin clay layer was found to have an extraterrestrial chemistry. This layer is unique in the geological record-it can be found all around the world and contains material that originated from the asteroid and Chicxulub impact site. To date, no models have been able to adequately explain how these impact ejecta traveled all around the world. In this paper we show that intense interactions between the high-velocity ejecta and atmosphere produce a fast-moving dust cloud, which is able to transport these ejecta much further than previously thought.