Short gamma ray bursts could cause mass extinction

Short gamma ray bursts could be more damaging to life on Earth than longer ones, says a Washburn University astrophysicist who’s been studying data from the SWIFT satellite.

Gamma ray events such as those caused by supernovae can deplete stratospheric ozone, allowing the most powerful and damaging forms of ultraviolet radiation to reach the Earth’s surface.

However, says astrophysicist Brian Thomas, the one-second bursts of gamma rays caused by the collision of two black holes or neutron stars are even more harmful.

“We find that a kind of gamma ray burst – a short gamma ray burst – is probably more significant than a longer gamma ray burst,” says astrophysicist Brian Thomas of Washburn University. “The duration is not as important as the amount of radiation.”

Such events don’t happen often – about once per 100 million years in any given galaxy. But if one did happen here, the results would be devastating.

The first effect, says Thomas, would be to deplete the ozone layer by knocking free oxygen and nitrogen atoms so they can recombine into ozone-destroying nitrous oxides. These long-lived molecules keep destroying ozone until they rain out, potentially devastating the ozone layer that protects life on Earth.

And, says Thomas, it’s very likely that Earth has been exposed to such events scores of times over its history. He now hopes to establish whether any evidence of this has been left behind.

Astronomical evidence isn’t likely, he says, because the galaxy spins and mixes pretty thoroughly every million years, so any remnants of blasts are probably long gone from view.

There might, though, be evidence in the ground here on Earth.

Some researchers are looking at the isotope iron-60, for instance, which has been argued as a possible proxy for radiation events.

If isotopes like iron-60 can reveal the strata of the events, it then becomes a matter of looking for extinction events that correlate and examining which species died and which survived.

“I work with some paleontologists and we try to look for correlations with extinctions, but they are skeptical,” said Thomas. “So if you go and give a talk to paleontologists, they are not quite into it. But to astrophysicists, it seems pretty plausible.”