Megalodon Was Killed Off By Supernova Radiation That Caused Cancer and Mutations, Study Says

The megalodon—the biggest shark ever to exist—may have been driven to extinction by a supernova explosion 2.6 million years ago. Scientists have linked the celestial event to a mass extinction of marine megafauna by looking at a spike in radiation that would have caused major health problems for large sea creatures, including cancers and mutations.

The study, published in the journal Astrobiology, builds on previous work from 2016 and 2017 that linked a series of supernova—an exploding star—150 light years away to an extinction on Earth. During this extinction event, about 36 percent of the marine megafauna were wiped out.

Read more: Biggest mass extinction in Earth's history saw almost all life wiped out in the blink of an eye

After the supernova, Earth would have been bombarded with cosmic rays, showering the planet in muons—elementary particles similar to an electron. Muons are passing through us all the time and account for about a fifth of the radiation dose we receive. "When this wave of cosmic rays hits, multiply those muons by a few hundred," Adrian Mellot, lead author of the latest study, said in a statement. "Only a small faction of them will interact in any way, but when the number is so large and their energy so high, you get increased mutations and cancer—these would be the main biological effects.

"We estimated the cancer rate would go up about 50 percent for something the size of a human—and the bigger you are, the worse it is. For an elephant or a whale, the radiation dose goes way up."

Mellot, from the University of Kansas, and colleagues have looked at the event more closely and come to the conclusion that there was probably a series of supernovae producing a cascade of cosmic rays—rather than just a one off burst. They then worked out how different habitats would have been affected—and found creatures living in shallower waters would have had a higher dose of radiation.

They found the radiation would have persisted "for at least the lifetime of marine megafauna," adding that it is "reasonable to hypothesize that this increase in radiation load may have contributed to a newly documented marine megafaunal extinction at that time."

This extinction included the megalodon—a shark that could grow up to 60 feet in length. "They just disappeared about that time," Mellot said. "So, we can speculate it might have something to do with the muons. Basically, the bigger the creature is the bigger the increase in radiation would have been."

Brian C. Thomas, Professor, Physics and Astronomy at Washburn University, was one of the scientists who initially found the supernova and extinction link. Thomas, who was not involved in the latest study, said the paper was an "interesting addition" that helps fill in our understanding of the supernova impact picture.

"It's really [a] new twist on the usual story that a supernova destroys ozone, which increases ultraviolet light, which harms organisms, especially smaller ones," he told Newsweek. "Our work showed that in this case the UV effect is not that big, but this other impact isn't something people have really thought much about before and it could be significant. I'd say I do agree with the conclusions, which basically say that large ocean-dwelling organisms would be at greater risk from the supernova radiation. Of course it's hard to directly connect this with the extinction event, but I think it's reasonable to claim it's a contributor."

Other theories about why megalodon went extinct include climate change, a decline in food supply and being outcompeted by new marine predators. Finding conclusive evidence is challenging, however. Because shark skeletons—including megalodon—are made of cartilage, the only thing remaining of them is their teeth. As a result, scientists must try to reconstruct the ancient world they dominated to find major changes that could have led to the species decline.