Firestorms as Part of the KT Extinction

K-Pg extinction: Reevaluation of the heat-fire hypothesis

Authors:

1. Douglas S. Robertson (a)
2. William M. Lewis (b)
3. Peter M. Sheehan (c)
4. Owen B. Toon (d)

Affiliations:

a. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA

b. Department of Ecology and Evolutionary Biology and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA

c. Department of Geology, Milwaukee Public Museum, Milwaukee, Wisconsin, USA

d. Department of Atmospheric and Oceanic Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA

Abstract:

The global debris layer created by the end-Cretaceous impact at Chicxulub contained enough soot to indicate that the entire terrestrial biosphere had burned. Preliminary modeling showed that the reentry of ejecta would have caused a global infrared (IR) pulse sufficient to ignite global fires within a few hours of the Chicxulub impact. This heat pulse and subsequent fires explain the terrestrial survival patterns in the earliest Paleocene, because all the surviving species were plausibly able to take shelter from heat and fire underground or in water. However, new models of the global IR heat pulse as well as the absence of charcoal and the presence of noncharred organic matter have been said to be inconsistent with the idea of global fires that could have caused the extinctions. It was suggested that the soot in the debris layer originated from the impact site itself because the morphology of the soot, the chain length of polycyclic aromatic hydrocarbons, and the presence of carbon cenospheres were said to be inconsistent with burning the terrestrial biosphere. These assertions either are incorrect or have alternate explanations that are consistent with global firestorms. We show that the apparent charcoal depletion in the Cretaceous-Paleogene layer has been misinterpreted due to the failure to correct properly for sediment deposition rates. We also show that the mass of soot potentially released from the impact site is far too low to supply the observed soot. However, global firestorms are consistent with both data and physical modeling.