Our planet saw a lot of action as the Pliocene Period gave way to the Pleistocene 2.6 million years ago. The world cooled off, Africa dried out, the poles froze over lowering global sea levels, and a series of repeated glaciations, or ice ages, began.
This change in climate has been blamed for the simultaneous extinctions of a number of marine megafauna species, including the largest and most powerful predator to have ever lived—the megalodon. This giant prehistoric shark grew up to 60 feet long with teeth as long as your forearm and a bite force of 25,000 to 40,000 lbf (pounds of force).
A severe drop in species diversity would surely have impacted the sharks’ diet of whales, seals, and other large prey, and shallower seas may have isolated them from their coastal nursery areas. Yet some say megalodon populations were so abundant during the Pliocene that a much more globally devastating change would have been required to force them into extinction.
A published in Astrobiology presents some compelling evidence linking the megalodon extinction to another catastrophic event that took place 2.6 million years ago. Led by Adrian Melott, professor emeritus of physics and astronomy at the University of Kansas, the study proposes that a supernova, or perhaps a whole bunch of them, may be to blame. Sediment core samples taken from ancient seabeds show a huge spike in radioactive particles right around the time when the megalodon disappeared.
When a massive star uses up most of its hydrogen and helium, it implodes on itself, blasting powerful shockwaves far out into space. If this happens close to home—within 160 light-years of Earth, give or take—the high-energy cosmic rays penetrate the atmosphere. “They tear up molecules, they can rip electrons off atoms, and that goes on right down to the ground level,” Melott, increasing the planet’s radiation exposure by a factor of three.
Isotopes such as iron-60 are telltale signs of exploding star events, as are subatomic particles called muons, which form when cosmic radiation interacts with the atmosphere. Harmless in small amounts, muons are 200 times heavier than electrons and can penetrate hundreds of feet of solid rock without interacting. In high doses, however, they cause mutations and cancers in living cells. After a supernova, everything on Earth would have been exposed to 20 times the normal muon load. The larger the creature, the higher the chance of mutations. Megalodon, once the largest creature on earth, would have been a muon magnet.
Guess what else happened 2.6 million years ago? The earth’s magnetic field flipped. Magnetic north and magnetic south experienced a geomagnetic reversal, an event which marks the start of the Quaternary Period. Typically, cosmic rays are diverted by the magnetic field toward the poles, except during a reversal, when they become dispersed, further exposing land and especially sea creatures to unprecedented levels of muon radiation.
Even an 11-foot jaw loaded with seven-inch teeth can’t compete with that.