Gamma Ray Burst HOW DEADLY WOULD A NEARBY GAMMA RAY BURST BE? Despite the obvious doom and gloom associated with mass extinctions, they have a tendency to capture our imagination. After all, the sudden demise of the dinosaurs, presumably due to an asteroid strike, is quite an enthralling story. But not all mass extinctions are quite as dramatic and not all have an easily identified culprit. The Ordovician extinction — one of the “big five” in Earth’s history — occurred around 450 million years ago when the population of marine species plummeted. Evidence suggests that this occurred during an ice age and a gamma ray burst is one of several possible mechanisms that may have triggered this extinction event. Gamma ray bursts (GRBs) are the brightest electromagnetic blasts known to occur in the Universe, and can originate from the collapse of the most massive types of stars or from the collision of two neutron stars. Supernovae are stellar explosions that also can send harmful radiation hurtling towards Earth. Both GRBs and supernovae are usually observed in distant galaxies, but can pose a threat if they occur closer to home, where they can strip the Earth’s upper atmosphere of its protective ozone layer leaving life exposed to harmful ultraviolet radiation from the Sun. A new paper, titled “Ground-Level Ozone Following Astrophysical Ionizing Radiation Events – An Additional Biological Hazard?” published in the journal Astrobiology took a look at the ramifications of a nearby GRB or supernova and the effects on life. The research was funded by the Exobiology and Evolutionary Biology element of the NASA Astrobiology Program.