Watch: How Gamma Ray Bursts Could Wipe Out Life on Earth
To sci-fi fans, gamma rays are best known as the driver of Hulk's origin story. But while there's no scientific proof that gamma radiation can turn you into a giant green superhero (yet), gamma ray bursts could theoretically be responsible for the realization of another sci-fi trope: an apocalypse.
Gamma ray bursts are huge explosions that are associated with supernovae, and are likely the result of the cores of extremely massive stars collapsing into black holes. They are the brightest electromagnetic events observed in the universe thus far, and they're fairly common. Massive stars, or "cosmic snipers," are firing gamma ray bursts all the time, and they often hit Earth. We detect approximately one per day, but so far they've all originated outside of our galaxy, which is too far away to hurt us. However, if it were ever within the Milky Way, scientists theorize that it could cause a mass extinction event.
But even a more distant GRB could still end life on Earth. And it wouldn't need to score a head-shot to kill us."
According to the above video, even if the GRB originated from a few thousand light years away, the burst would be a hundred light years wide by the time it reaches Earth. Since the ozone layer is only suited to protecting us from ultraviolet radiation, the gamma radiation would overwhelm it, leaving life on Earth to be killed by deadly solar radiation. The ozone layer would replenish itself eventually, but it would take long enough that the Sun would burn the Earth completely sterile, at least when it comes to complex life forms.
And because gamma ray bursts are so common, they may be the reason why intelligent life (and life in general) seems to be so rare in the Universe. There's no way to prove this yet, but it's possible that GRBs have wiped out life forms en masse in other galaxies. As a result, scientists believe that only 10% of galaxies are potentially habitable for complex life.