Extraterrestrial impacts and wildfires

Small extraterrestrial impacts are inefficient at starting fires, and the evidence connecting larger impacts with wildfires is not secure. The association between impacts and wildfires has been re-assessed by reviewing records of recent small impacts, examining material incorrectly identified as ‘charcoal’ from the Miocene Ries impact crater, and charcoal from K–T boundary sediments. Fossil charcoal was collected from five well-researched K–T sites, and examined using scanning electron microscopy and reflected light microscopy. An important discovery was that a significant proportion (53%) of the charcoal fragments examined, from all five sites, displayed features interpreted as resulting from biodegradation prior to being charcoalified. Furthermore, there was a complete absence of morphological features recognised as resulting from the charring of living plants. The clear inference from this observation is that there could have been a significant time lag (months, years, and possibly decades) between plant mortality and the fire(s) that preserved them as charcoal, maybe involving accelerated drying-out due to impact-related atmospheric processes. These results do not support or oppose the extraterrestrial impact hypothesis, but do suggest that any putative impact(s) was not immediately followed by ‘global’ wildfires.