For a while we’ve known that supernova in the past few million years probably showered Earth with radiation. And a new study has looked at the impact they may have had on life on Earth.
As picked up by Astrobiology Magazine, a researcher has suggested that nearby stars exploding could have depleted our planet’s ozone layer. Dr Brian Thomas from Washburn University in Kansas looked at the effects of such events around the Pliocene-Pleistocene, about 5 million years ago.
We know of at least one supernova at a distance of 163 to 326 light-years (50 to 100 parsecs) from Earth about 2.5 to 8 million years ago, based on iron found in the fossil record, and there are likely more. At such a distance, while too far to have directly caused mass extinctions, increased ultraviolet radiation from them could have played a part.
“We conclude that biological impacts due to increased [ultraviolet] irradiance in this [supernova] case are not mass-extinction level but might be expected to contribute to changes in species abundances,” he wrote in the paper.
The issue stems from that ozone depletion. You might remember that a pretty intense ozone hole was found above the Antarctic back in 1985, resulting in a global effort to fix it. At the time, though, the ozone was depleted by up to 60 percent.
The ozone depletion caused by supernovae studied by Dr Thomas would not have been so severe. But they would have occurred over a much longer period of time, which could have been pretty disastrous for some life.
“While our [supernova] case results have smaller depletion values, the duration and spatial extent are much larger, with near global coverage, sustained for centuries,” he wrote.
Animals, even early human ancestors in Africa about 2.5 million years ago, could have been at risk of DNA damage as a result of the depletion. He looked at a number of other effects too, including cataracts and plant damage, and found they generally got worse, particularly in higher latitudes.
But he noted to Astrobiology Magazine that a supernova going off in our vicinity may not simply “wipe out everything,” but instead cause gradual changes. For example, between 58 and 77 percent of mammal species are thought to have been replaced between 3 and 1.8 million years ago.
It doesn't look like, in this time period, supernovae caused any mass extinctions on Earth. But they may well have played a part in some smaller extinction events.
(H/T: Astrobiology Magazine)