From: Adrian Melott [view email]
Date: Tue, 29 Mar 2005 16:18:37 GMT   (226kb)

It is likely that one or more gamma-ray bursts within our galaxy have strongly irradiated the Earth with X-ray and gamma-ray photons in the last Gy. This produces significant atmospheric constituent ionization and dissociation, resulting in ozone depletion and DNA-damaging ultraviolet solar flux reaching the surface for up to a decade. Here we show the first detailed computation of two other significant effects. Visible opacity of NO2 is sufficient to reduce solar energy at the surface up to a few percent, with the greatest effect at the poles. This may be a sufficient climate perturbation to initiate glaciation. Rainout of dilute nitric acid is a primary atmospheric removal mechanism for odd nitrogen compounds, which can temporarily boost fertility in terrestrial and shallow water ecosystems. These results support the hypothesis that the late Ordovician mass extinction may have been initiated by a gamma-ray burst, in that it was accompanied by glaciation, 13C isotope abundance excursions, and followed by significantly expanded terrestrial flora.

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