Did a supernova cause the Devonian mass extinction event?

359 million years ago the Earth suffered one of its worst extinction events, and a team of researchers at the University of Illinois think that it might be caused by a series of supernova explosions no more than 35 light years away.

Every once in a while something disastrous happens to life on Earth. The biggest episodes we call extinction events. The latest big one happened about 65 million years ago, and was a very rough time for dinosaurs but turned out pretty awesome for the mammals. But that extinction event was just the latest in a long series of interruptions in the multitude of life on the planet. One of the earliest extinction events happened at the boundary of the Devonian and Carboniferous periods about 359 million years ago.

We’re not exactly sure what triggered that extinction event. There’s no clear smoking gun like there is for the asteroid impact evidence of the one that killed most of the dinosaurs. But a team of researchers from the University of Illinois are proposing a radical and otherworldly explanation: supernovae.

An artist’s impression of Betelgeuse. Its surface is covered by large star spots, which reduce its brightness. During their pulsations, such stars regularly release gas into their surroundings, which condenses into dust. Image Credit: MPIA graphics department

The key piece of evidence leading to this hypothesis is the fact that fossils of plants remaining from that tumultuous era show signs of nasty sunburns: excess UV exposure. The ozone layer of the Earth does a fantastic job of blocking almost all the UV radiation from the sun, so the fact that these critters were getting an extra dose means that our ozone layer had to be depleted. There are a lot of potential geological processes that can scrub away our ozone layer, and there’s also one celestial one.

The intense radiation from a close enough supernova blast can strip away our ozone, leaving the surface of the Earth exposed to the UV onslaught from the sun. In general, intense UV radiation isn’t too great for living beings, hence an extinction event.

The researchers estimated that a single supernova blast within 65 light years could have been enough to suppress our ozone layer for about 100,000 years. The fossil record indicates that life was having a tough go at it for three times that length, however, so the researchers speculate that the supernova wasn’t alone. This isn’t a crazy idea, as stars do tend to cluster and big stars do tend to go off as supernova relatively close by.

But as of yet this is an untested hypothesis. The next step is to find evidence in those fossil layers of an excess of certain radioactive elements like plutonium-244. This element isn’t naturally produced on the Earth, and so the only way for it to exist in that layer of sediment is for it to have been put there as the shock-wave of the supernova washed over our planet.

If you’re worried about the next supernova blast, don’t stress out. The nearest supernova candidate to the Earth is the star Betelgeuse, which is located a safe 600 light years away.