For tens of millions of years, Earth’s oceans were crowded with 5,000-lb. (2,200 kilograms) turtles, whale-size sea cows and sharks as large as school buses. Then, about 2.6 million years ago, they started dying in droves.
The mass die-off known as the Pliocene marine megafauna extinction may have wiped out more than a third of Earth’s large marine species (including the beloved megalodon — a Jaws-like shark that measured up to 80 feet, or 25 meters, long). Today, scientists still don’t know exactly why it happened. Climate change was definitely a factor; it was the start of a new Ice Age in which glaciers began replacing oceans, and coastal food sources were severely diminished. But did climate change alone cause this deadly event, or are there more pieces to this deadly puzzle? [Wipeout: History’s Most Mysterious Extinctions]
A new paper scheduled to be published in the 2019 edition of the journal Astrobiology suggests one bold possibility: Perhaps exploding stars helped slay the giants of the deep.
According to Adrian Melott, lead study author and professor emeritus of physics and astronomy at the University of Kansas, there is evidence that a nearby supernova — or possibly a string of multiple supernovas — coincided with the start of the great die-off that rid the world of its largest marine life. If these stellar explosions were strong enough and close enough to Earth, they could have drenched the world in stellar radiation, gradually raising the incidence of mutation rates and cancers among Earthly fauna for hundreds of years. The larger an animal was, Melott wrote in the new study, the more radiation they were likely to absorb, thus worsening their chances for survival.
“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,” Melott said in a statement. “For an elephant or a whale, the radiation dose goes way up.”