In Ends of the World: Gamma-Ray Bursts, I raised the possibility that millions of years ago, Earth may have experienced a catastrophic gamma-ray burst, an immense beam of energy that forms when high-mass stars collapse, or after a collision between binary neutron stars.
Well, a new study claims that it actually may have happened, but much more recently than I’d thought: The 8th Century.
“Last year, a team of researchers found that some ancient cedar trees in Japan had an unusual level of a radioactive type of carbon known as carbon-14.
In Antarctica, too, there was a spike in levels of a form of beryllium – beryllium-10 – in the ice.
These isotopes are created when intense radiation hits the atoms in the upper atmosphere, suggesting that a blast of energy had once hit our planet from space.”
– Gamma-ray burst ‘hit Earth in 8th Century’, BBC News
Whatever the cause of this increase in radiation, scientists were able to narrow the event down to between AD 774-775. The Middle Ages.
The curious thing, however, is that this particular gamma-ray event (if it was a gamma-ray) did not have a catastrophic impact on the planet, as one would expect. To account for this, researchers calculated the distance from Earth the burst would have been to leave the traces of radiation they observed. They concluded it was “3,000 to 12,000 light-years away.”
Just far enough, apparently, for our atmosphere to shield us from a potential mass-extinction event.
I don’t know.
Maybe we got lucky. Maybe they’re wrong (it could have, for example, been a major solar flare). While the chances of being blasted by a gamma-ray burst again are slim, we shouldn’t get comfortable: these things can melt our atmosphere, boil our planet’s surface, and leave anyone who survives vulnerable to other harmful cosmic rays.
A bad day on Earth, indeed.
Image Credit: NASA/DOE/Fermi LAT Collaboration, Capella Observatory.