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Top Comments: Supernovae May Have Caused Two of Earth's Five Great Extinctions [1]
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Date: 2025-04-03
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I have nothing unique to say regarding the tariffs or the stock market implosion, but, yes, I’m as anxious as anyone else about it. I’ve decided to retreat to my comfort zone—science (which faces its own challenges in the age of Trump).
A new report out of Keene University in England has found support for the notion that two of the great extinctions that have occurred on Earth, specifically the late Ordovician, which occurred 445 million years ago, and the late Devonian, which occurred 372 million years ago, were caused by supernovae of stars nearby our Solar System. The Ordovician extinction killed about 60 % of marine life at a time when most of life was found in the ocean. The Devonian extinction killed off about 70 % of life on the planet.
The researchers were attempting to count the number of supermassive stars (classified as OB stars) in the Milky Way within a radius of about 3,260 lightyears. Supermassive stars are the type of stars that undergo supernova explosions at the end of their lives. [Briefly, the process of nuclear fusion that generates the energy put out by the star ceases when it runs out of fuel. When there is no longer an energy output pushing against the mass of the star itself, the star begins to collapse, becoming hotter as it does so. Most of the material of the star then ricochets of the core of the star and causes a spectacular explosion, accompanied by various forms of intense radiation.] The purpose of the study was to determine the rate at which such stars form in the Milky Way, as subsequently, the rate at which they explode as well.
However, only supernovae that take place within about 65 lightyears are the ones that could cause an extinction. When they calculated the frequency of supernovae in our stellar neighborhood, it happened to agree with the frequency of mass extinctions on Earth. Now, we know that the most recent mass extinction, at the end of the Cretaceous, was caused by an asteroid impact, and we know that the Permian extinction (the biggest one) is usually blamed on excessive vulcanism and associated climate instability.
Were a supernova to occur near the Solar System, the Earth would be undergo intense irradiation. Such direct irradiation could be fatal to organisms exposed to it, but worse, the radiation would deplete the Earth’s stratospheric ozone layer, which shields the Earth from damaging ultraviolet radiation from the Sun. While the UV radiation from the Sun would not be as intense as the radiation from the supernova, it would last much longer, causing DNA damage in exposed organisms. As it happens, both of these extinctions are believed to be linked to ozone depletion.
Interestingly, while being too close to a supernova can cause an extinction event to occur, supernovae can also be said to seed the stuff of life. The explosions distribute the heavier elements created by the fusion process that fuels the star throughout the region, and the stuff of life is made out of those heavier elements.
This study is not definitive, but it shows that blaming an extinction on a nearby supernova is not crazy. Fortunately for us, the nearest class OB star to us (Antares and Betelgeuse) are too far away to damage the Earth when their times come for a supernova.
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