How do you wipe out an entire species of 60 ft long giant sharks? Blow up a star, of course. According to a recent paper, supernovas may have been the cause of a number of unexplained mass extinctions throughout earth's history, including the monstrous and fantastically named giant shark species Megalodon, a relative of the great white shark, whose mysterious extinction some 2.6 million years ago has long puzzled scientists.
There are enough out there to confidently say that stars are exploding all the time. Luckily for us, space is big and our lives are relatively short, so the chance of us getting blasted by a supernova are pretty small. Still, sometimes it happens (roughly every 100 million years) and the earth gets whacked by a cloud of radiation that once made up some other poor solar system's sun. Scientists have been looking for evidence of how cosmic events like supernovas impact earth and the recent study attempts to discover the role that they play in the rise and fall of species here on earth and the impact that they might have had on evolution. If you guessed that an exploding star would be really good at killing things, you're right!
According to Adrian Melott, astrophysicist at the University of Kansas and the author of the new paper, the mass extinction of megafauna like the Megalodon lines up with evidence of a supernova impacting earth. Isotopes of iron-60, which is extremely rare on earth yet common in supernovas, were found on the sea floor and the surface of the moon. Dating these isotopes reveals that, if they were dropped here by a supernova, that supernova rolled through our solar system 2.6 million years ago—right about when the Megalodon checked out. According to Melott:
“A lot of things would not leave a definite residue. [Iron-60] is smoking-gun evidence of something happening.”
The blast from a supernova could end species in a few ways. Other theories on how supernovas could impact mass extinctions point to indirect causes. The blast from a supernova could strip the earth's ozone layer, for example, leaving species vulnerable to solar radiation and destroying ocean food sources like plankton and coral reefs. Cosmic rays could also seed clouds and create a "cosmic-ray winter," according to Henrik Svensmark of the Technical University of Denmark, which would also result in the destruction of food sources.
Melott thinks that the supernova may have been a much more direct cause of the extinction, however. Supernovas release highly charged radioactive particles called muons. Getting hit by a cloud of muons probably wouldn't feel like much at first, but the radiation exposure would soon cause irreparable genetic damage and mutations that, depending on the species, could be catastrophic. The bigger the animal, the worse the impact would be. For an animal the size of a human, the muon storm would increase cancer rates by 50 percent. Considering that the Megalodon was about the size of a school bus, it would get hit pretty hard.
As evidence for his theory, Melott points to the sudden extinction of 36 percent of ocean species 2.6 million years ago at the end of the Pliocene era and the beginning of the Pleistocene. The extinct species were largely coastal dwelling, where the impact from muon radiation would be the most devastating. Unfortunately, highly radioactive particles like muons don't leave any record of their presence, so it's hard to tell just how catastrophic an impact it was. Yet there does seem to be a correlation between a supernova and a mass extinction, so it is likely that there was some sort of connection.
So, if you have a fear of shark infested waters, just remember: there's always something bigger and badder on its way (but probably not for another 97 million years).