UV-B RADIATION WAS THE DEVONIAN-CARBONIFEROUS BOUNDARY TERRESTRIAL EXTINCTION KILL MECHANISM

There is an unexplained terrestrial mass extinction at the Devonian-Carboniferous boundary (359 million years ago). The discovery in East Greenland of highly aberrant malformed land plant spores demonstrates that the extinction was coincident with elevated UV-B radiation demonstrating ozone layer reduction. Mercury data through the extinction level proves that, unlike other mass extinctions, there were no planetary scale volcanic eruptions. Significantly, the Devonian-Carboniferous boundary terrestrial mass extinction is embedded within a single lacustrine cycle that represents a major episode of climatic warming as seasonal rainfall reached into the interior of the Old Red Sandstone Continent to forms a large, stratified permanent lake. This represents the collapse of the short but intense final glacial cycle of the latest Famennian ice age. A mechanism for ozone layer reduction during rapid warming is increased convective transport of ClO. In this situation ozone loss during rapid warming becomes an inherent Earth System process with the unavoidable conclusion that we should be alert for such an eventuality in the future warming world. The discovery of these malformed spores at the Devonian-Carboniferous boundary in the absence of any evident Large Igneous Province has stimulated interest in previous explanations for elevated UV-B radiation including cosmic ray burst from a Supernova and a hyperactivity in the Earth's magnetic field.