Gamma-Ray Bursts as a Threat to Life on Earth

TL;DR

Gamma-ray bursts could have caused significant atmospheric and biological impacts on Earth over the last billion years, including ozone depletion, increased UV radiation, and climate effects, with implications for understanding past extinction events.

Contribution

This study uses a two-dimensional atmospheric model to quantify the effects of gamma-ray bursts on Earth's atmosphere and biosphere, providing new estimates of potential impacts.

Findings

GRBs can deplete Earth's ozone layer significantly.

Increased UVB radiation damages DNA and affects life.

NO2 from GRBs can cause global cooling and nitrate deposition.

Abstract

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 kiloparsecs would quickly deplete much of the Earth's protective ozone layer, allowing an increase in solar ultraviolet 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. In this paper I give a concise review of this work and discuss current and future work on extending and improving our estimates of the terrestrial impact of a GRB.