The Pliocene-Pleistocene extinction event was preceded by a supernova explosion, which would have showered the Earth with harmful radiation, causing cancers and mutations in the planet’s largest animals.
Approximately 2.6 million years ago, at the beginning of the Pleistocene Epoch, Earth went through a mass extinction event that wiped out the giant beasts dwelling in the planet’s oceans. Among them was the fearsome Megalodon (Carcharocles megalodon), an enormous shark species that could grow up to 60 feet in length — or about the size of a school bus.
The intriguing thing about this mass extinction is that it seemed to coincide with a major celestial event, namely the death of a massive star found some 160 light-years from Earth, or about 50 parsecs, notes Science Daily.
In a new study published last month in the journal Astrobiology, a team of scientists explores whether there was any type of connection between the two destructive events that marked our planet’s distant past.
This is not the first time that researchers have examined a possible link between colossal stellar explosions, known as supernovae, and mass extinctions on Earth. As the Inquisitr previously reported, earlier this year another study argued that two nearby supernovae, which exploded 2.5 million and 8 million years ago, would have pummeled our planet with ionizing radiation, thereby depleting Earth’s ozone layer and influencing a series of mass extinctions that occurred later on.
This latest research suggests that one of these two supernovae may have also been behind the mass extinction event recorded at the boundary between the Pliocene and the Pleistocene, which killed off a third of the organisms living on Earth and brought on the demise of the ocean megafauna.
This particular supernova occurred a few hundred years after the start of the Pleistocene, or about 2.5 million years ago, and bathed the Earth in cosmic rays, showering the planet with a radioactive isotope known as iron-60. Recently uncovered in ancient seabed deposits from all around the world, this isotope couldn’t have formed on Earth, its only possible source of origin being a supernova explosion.
According to study lead author Adrian Melott, professor emeritus of physics and astronomy at the University of Kansas, the data offers a unique window into the history of our planet.
“We have evidence of nearby events at a specific time. We know about how far away they were, so we can actually compute how that would have affected the Earth and compare it to what we know about what happened at that time.”
The same cosmic event, which was likely part of a series of supernovae that shaped the Local Bubble — a cavity in our galaxy’s interstellar medium, located in the Orion Arm of the Milky Way, where our solar system also resides — was also responsible for a rain of penetrating particles known as muons.
Described as very large electrons, about 200 times more massive than the negatively charged components of atoms, muons are extremely invasive particles that penetrated more than half-a-mile into ocean waters. Once there, these particles lingered “for at least the lifetime of marine megafauna,” the authors wrote in their paper. Deep underwater, these muons caused cancers and mutations, particularly affecting larger animals, reports Science Daily, citing the University of Kansas.
“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,” explained Melott, who dedicated the last 15 years of his career to the study of Earth’s mass extinction events.
As he pointed out, Megalodon disappeared around the same time. “We can speculate it might have something to do with the muons,” remarked Melott.
The scientists are unsure whether the cause of all these phenomena was a single powerful supernova or an entire series of stellar explosions — perhaps the very supernovae chain that created the Local Bubble.
“I kind of favor a combo of the two — a big chain with one that was unusually powerful and close. If you look at iron-60 residue, there’s a huge spike 2.6 million years ago, but there’s excess scattered clear back 10 million years,” said Melott.
“There really hasn’t been any good explanation for the marine megafaunal extinction. This could be one. […] We now can get really definite about what the effects of radiation would be in a way that wasn’t possible before.”
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