Gamma-Ray Bursts and the Earth: Exploration of Atmospheric, Biological, Climatic and Biogeochemical Effects

Gamma-Ray Bursts (GRBs) are likely to have made a number of significant impacts on the Earth during the last billion years. The gamma radiation from a burst within a few kpc would quickly deplete much of the Earth’s protective ozone layer, allowing an increase in solar UVB radiation reaching the surface. This radiation is harmful to life, damaging DNA and causing sunburn. In addition, NO2 produced in the atmosphere would cause a decrease in visible sunlight reaching the surface and could cause global cooling. Nitric acid rain could stress portions of the biosphere, but the increased nitrate deposition could be helpful to land plants. We have used a two-dimensional atmospheric model to investigate the effects on the Earth’s atmosphere of GRBs delivering a range of fluences, at various latitudes, at the equinoxes and solstices, and at different times of day. We have estimated DNA damage levels caused by increased solar UVB radiation, reduction in solar visible light due to NO2 opacity, and deposition of nitrates through rainout of HNO3. For the “typical” nearest burst in the last billion years, we find globally averaged ozone depletion up to 38%. Localized depletion reaches as much as 74%. Significant global depletion (at least 10%) persists up to about 7 years after the burst. Our results depend strongly on time of year and latitude over University of Kansas, Department of Physics and Astronomy, Lawrence, KS 66045-7582; [email protected], [email protected], [email protected], [email protected], [email protected] Laboratory for Atmospheres, NASA Goddard Space Flight Center, Code 613.3, Greenbelt, MD 20771; [email protected], [email protected] Laboratory for Astroparticle Physics, NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771; [email protected], [email protected] Also at Haskell Indian Nations University After August, 2005, at Washburn University, Department of Physics and Astronomy, Topeka, KS 66621; [email protected]