WILDFIRE EFFECTS: Large impact cratering events can produce wildfires over vast portions of the Earth's surface.  In the case of the Chicxulub impact event that has been linked to dinosaur extinction, the wildfires affected vast portions of the world and sent plumes of smoke into that atmosphere that darkened the planet.
    Soot from the fires was carried by winds around the world and eventually settled to the ground where it accumulated on top of the debris that was ejected from the Chicxulub crater and also distributed globally.

    These wildfires were devastating.  Not only did they consume vegetation, they also destroyed important habitats and food resources for animals, possibly leading to the collapse of the food chain in continental regions.  This and other impact-generated environmental effects led to the extinction of over 75% of the species.
 

THE EVIDENCE: The first evidence of these fires was found by Wendy Wolbach, Ed Anders, Roy Lewis, and Iain Gilmour at the University of Chicago.  They found traces of the soot in the rocky remnants of the impact event that were scattered in places like Denmark, New Zealand, Spain, Turkmenia, and the United States, far from the point of impact in what is now Mexico.
  The fossil record also contains a biological signature of the wildfires. A detailed study by Tschudy and Chuck Pillmore with the U.S. Geological Survey discovered a fern-spore spike in the rock record.  This is an anomolous concentration of the spores shed by growing ferns, relative to the pollen shed by other types of plants (e.g., angiosperms) that grew soon after the impact event.
    The anomalously high amount of fern spores indicates that ferns were the first large plants to regrow on the fire-ravaged landscape. Many years later, other plants, like flowering bushes and eventually trees, began to grow.
This fire-recovery pattern is similar to that seen in some parts of the world today.  For example, after a forest fire in New England, ferns are often the pioneering plant that grows first.  Many years are needed for birch forests, and eventually hardwood maple forests, to recover.
ATMOSPHERIC HEATING: Jay Melosh at the University of Arizona and several of his colleagues realized that the post-impact fires were produced when impact ejecta superheated the atmosphere.  Some of the debris ejected from the Chicxulub crater rose above the Earth's atmosphere before it rained back down to Earth.  The particles of material in the ejecta plume, just like falling meteors, heated the atmosphere.  There was so much debris falling through the atmosphere at the same time, that it heated the atmosphere to far higher temperatures than individual meteors. A large fraction of this heat was radiated to the ground, raising surface temperatures to several hundreds of degrees and causing vegetation to burst into flames.

    New model calculations of these processes by David Kring (Univ. Arizona) and Daniel D. Durda (Southwest Research Institute) show how the fires were ignited, initially around the impact site and, soon afterwards, at a spot on the opposite side of the Earth where a concentrated stream of debris rained back down on Earth.  As the Earth rotated below the impact ejecta, the fires spread to the west of these two locations over the following hours to days.  Fires were ignited in North America, South America, Africa, and Asia. Depending on the trajectory of the impacting asteroid or comet, and details in the expanding plume of impact ejecta, fires may have also been ignited in Antarctica or Europe.

    These wildfires poured vast amounts of pollutants into the atmosphere. Based on the amount of soot found in sediments deposited soon after the impact event, it has been estimated that ten trillion metric tons of carbon dioxide (CO2), one-hundred billion tons of methane (CH4), and one trillion tons of carbon monoxide (CO) were pumped into the atmosphere.  These pollutants contributed to the environmental catastrophe of the Chicxulub impact event and may have been partly reponsible for the mass extinction event.
 
 


This web site is part of the NASA/UA Space Imagery Center's Impact Cratering Series.
Concept and content by David A. Kring and Jake Bailey.
Movie of impact generated wildfires compiled by Daniel D. Durda.
Design, graphics, and images by Jake Bailey and David A. Kring.
All information and images are the property of the Space Imagery Center.
    To obtain usage permission, contact the Data Manager - Maria Schuchardt at mariams@pirl.lpl.arizona.edu