New Limits for Combustion in Low Oxygen Redefine Paleoatmospheric Predictions for the Mesozoic

Numerous studies have sought to test combustion under varying concentrations of oxygen however, none have been able to assess the limits of combustion within a fully controlled and realistic atmospheric environment. Experimental burns were performed at 20 degrees centigrade at oxygen concentrations ranging from 9 to 21%, and at ambient and high (2000ppm) carbon dioxide, in a new experimental atmospheres and climate facility, equipped with a thermal imaging system and full atmospheric, temperature and humidity control. Our data reveal that the lower oxygen limit for combustion within the long-held “fire window” (12-35%) should be increased from 12 to 15%. These results, coupled with a new record of Mesozoic paleowildfires are incompatible with the prediction of prolonged intervals of super-low atmospheric oxygen levels (10-12%) in the Mesozoic. Paleowildfire provides a key proxy for testing super-low oxygen events in the geological record and must be studied in order to test hypotheses suggesting that short-term super-low oxygen periods drove faunal and floral diversity loss across major mass extinction events.