A real mystery is developing. In 2012 researchers found evidence that our planet had been struck by a blast of radiation during the Middle Ages, but there was debate over what kind of cosmic event could have caused this. Either a rare solar flare or an even bigger explosion, a gamma-ray burst seems to be the culprit. 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. Using tree rings and ice-core data, researchers were able to pinpoint that this would have occurred between the years AD 774 and AD 775, but the cause of the event was a puzzle.
Observations of deep space suggest that gamma ray-bursts are rare. They are thought to happen at the most every 10,000 years per galaxy, and at the least every million years per galaxy. If a cosmic explosion happened at the same distance as the 8th Century event, it could knock out our satellites. But if it occurred even closer – just a few hundred light-years away – it would destroy our ozone layer, with devastating effects for life on Earth.
Two teams of scientists, two different conclusions! That’s the way science works. Either more data, or a better developed theory will show which one is right. Until then, may the debate continue.