Abstract
The presence of charcoal in the geological record offers a new approach to assessing oxygen levels in palaeoatmospheres. Charcoal is formed by the incomplete combustion of woody tissues. The combustion of wood is supported by the generation of the combustible gases carbon monoxide and methane during the pyrolysis process. As the combustion ranges of these gases are restricted with decreasing oxygen availability to a level below which no combustion will occur, the production of charcoal and its appearance in the geological column constitute a record of changing oxygen availability through time. We show here that the occurrence of charcoal in rocks from the Lower Carboniferous onwards suggests that atmospheric oxygen never fell below 0.3 of present atmospheric level (PAL) during this time. Detrital charcoal formed by forest fire must have contributed an appreciable fraction to inert carbonaceous matter in sediments (kerogen) during post-Devonian time.
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