Both supernovae and extreme solar flares can damage Earth’s ozone layer. But perhaps a black hole swallowing a neutron star somewhere not too far away gives a bigger punch – lasting a second or so.
Although the gamma radiation can only hurt your skin for this one second, it much rather spends its time separating oxygen and nitrogen atoms – so these can then bind to form nitrous oxide and carry out space’s evil scheme: N2O is [apart from an important greenhouse gas] also damaging to the ozone layer [through NO] and can help deplete it for weeks on end [considering its atmospheric half-life of around 50 days].
That theory we just learned from astrophysicist Brian Thomas of Washburn University who yesterday gave a lecture about space radiation related extinction events at the annual meeting of the Geological Society of America.
Without our ozone protection life would suffer ultraviolet radiation damage and species could go extinct.
Ten gamma bursts per gigayear?
Still, for now, there seems little reason to redream your Cold War nightmares – this didn’t happen last couple of weeks, so probably it won’t occur tomorrow either.
On geological timescales however the probability becomes much larger, think astrophysicists working on the subject. New research now focuses on short gamma bursts especially, Thomas tells us, very short-lived dramatic events in outer space, like the collision of two neutron stars or the collision of two black holes.
As our own Milky Way galaxy is a self-restoring system, it’s hard to find evidence of any of this happening in the distant past. Space observations have however spotted the events in other galaxies [the far, far away type] and from these conclude in our galaxy the short gamma bursts could occur once every 100 million years.
This means Earth must have experienced tens of such blasts in its history. To see if these can be correlated to the mass extinction events from the fossil record Thomas encourages the assembled Earth scientists to go look for iron-60 isotopes, a possible clue.
“I work with some paleontologists and we try to look for correlations with extinctions, but they are skeptical,” he said. “So if you go and give a talk to paleontologists, they are not quite into it. But to astrophysicists, it seems pretty plausible.”
Better safe than sorry: more carbon and less ozone
That’s any scientist’s trait, to always look for the answers within own respective disciplines. For geologists it is simply more exiting to reconstruct moments when ancient supercontinents formed or broke up. But let’s acknowledge thus far the Earth scientists don’t really seem lost for own extinction theories. And apart from that one non-Baptistina asteroid at the Cretaceous-Tertiary extinction the fossil record shows quite often species disappearances don’t need tiny iridium layers or rare iron isotopes – usually one big self-enhancing carbon anomaly seems quite capable of doing the job: warming/cooling, acidification, anoxia.
But if ozone depletion and UV damage would turn out to be of importance to any of the historic mass extinctions, we can also mark that one on the checklist of our Holocene-Anthropocene project. If really you want to write planetary history, you’ve got to be thorough about it – one thing we can’t be denied.
© Rolf Schuttenhelm | www.bitsofscience.org