120 Paleontology II: Paleobotany and Behavior

Monday, 10 October 2011
1:30 PM - 5:30 PM
Room 205AB

THE FIREOX MODEL AND THE BASELINE FLAMMABILITY OF EARTH'S ECOSYSTEMS ESTIMATED FROM PALAEOATMOSPHERIC OXYGEN OVER THE PAST 350 MILLION YEARS

Paper number: 120-6
Program: Technical Sessions
Time: 2:45 PM – 3:00 PM

Authors

Abstract

Atmospheric oxygen is estimated to have varied greatly throughout Earth’s history and has been capable of influencing wildfire activity wherever fuel and ignition sources were present. Several studies have estimated atmospheric oxygen concentrations during Earth’s past. These studies reveal periods of both super- and sub- ambient atmospheric oxygen and, in some cases, superlow atmospheric oxygen (<15%) since the evolution of terrestrial life. Such estimates point to periods in Earth’s history when fire activity could have been significantly enhanced, suppressed, or even entirely switched off. The close-knit relationship between atmospheric oxygen concentration and fire means that it is essential to understand what minimum value of atmospheric oxygen limits combustion in order to estimate whether or not fire has ever been switched off during times of low atmospheric oxygen in Earth’s past.

We have used a strong electrical ignition source to ignite smoldering fires in one of the worlds most flammable natural plant based substances – dry peat. We measured the self-sustained propagation of these smoldering fires in atmospheres of different oxygen concentrations. These data have been used to build the FIREOX model that we use to estimate the baseline intrinsic flammability of Earth’s ecosystems according to variations in atmospheric oxygen over the past 350 million years (Ma). Our aim is to highlight times in Earth’s past when fire has been capable of influencing the Earth system. We reveal that fire activity would be greatly suppressed below 18.5% atmospheric oxygen, entirely switched off below 16% atmospheric oxygen, and rapidly enhanced between 19–22% atmospheric oxygen. We reveal that fire activity would have been high during the Carboniferous (350–300 Ma) and Cretaceous (145–65 Ma) periods; intermediate in the Permian (299–251 Ma), Late Triassic (285–201 Ma), and Jurassic (201–145 Ma) periods; and surprisingly low to lacking in the Early–Middle Triassic period between 250–240 Ma. Today fires consume huge quantities of biomass in all ecosystems and play an important role in biogeochemical cycles. Therefore these baseline variations in Earth’s flammability have far-reaching consequences for the evolution of life and Earth’s biodiversity over geological timescales.