Paper: astro-ph/0505472
Date: Mon, 23 May 2005 13:14:53 GMT (2081kb)
Title: Gamma-Ray Bursts and the Earth: Exploration of Atmospheric, Biological,
Climatic and Biogeochemical Effects
Authors: Brian C. Thomas (KU), Adrian L. Melott (KU), Charles H. Jackman
(GSFC), Claude M. Laird (KU), Mikhail V. Medvedev (KU), Richard S. Stolarski
(GSFC), Neil Gehrels (GSFC), John K. Cannizzo (GSFC), Daniel P. Hogan (KU),
and Larissa M. Ejzak (KU) (KU = University of Kansas, GSFC = NASA Goddard
Space Flight Center)
Comments: 68 pages, 20 figures, 12 tables; Submitted to ApJ
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Gamma-Ray Bursts (GRBs) are likely to have made a number of significant
impacts on the Earth during the last billion years. 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 $\mathrm{NO_2}$ opacity, and deposition of nitrates
through rainout of $\mathrm{HNO_3}$. 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 which the burst occurs. We find DNA
damage of up to 16 times the normal annual global average, well above lethal
levels for simple life forms such as phytoplankton. The greatest damage occurs
at low to mid latitudes. We find reductions in visible sunlight of a few
percent, primarily in the polar regions. Nitrate deposition similar to or
slightly greater than that currently caused by lightning is also
observed,
lasting several years. We discuss how these results support the hypothesis that
the Late Ordovician mass extinction may have been initiated by a GRB.