An ancient supernova might have caused one of the mass extinctions on Earth eons ago.

The extinction of the dinosaurs was probably caused by an asteroid. Though scientists have generalized that it was a potential trigger to one of the mass extinctions, yet there has been many more mass extinctions over the eons. There’s this extinction that’s quite recent — both in it’s timescale and in it’s discovery — that occurred roughly 2.6 million years ago, that killed off a staggering number of marine life and resulted in what’s known as the Pliocene epoch. Now here’s the catch: how did it happen? New research suggests that it was an ancient supernova. Like what?

 

Related media: Pliocene Epoch – Florida Fossils: Evolution of Life and Land

 

Once Upon An Element

Let’s clear up the mystery: There’s a matter of evidence that the Earth is abundant with iron-60 — an isotope of (you guessed it) iron. An isotope is just an atom of an element with an unusual amount of neutrons in it’s nucleus; iron-60 has 34 neutrons and 26 protons, whereas the iron in your blood — also known as iron-56 — has 30 neutrons and 26 protons.

Now here’s the story: In the 1990s, an astrophysicist named Brain Fields (and that’s the smartest-looking name for an astrophysicist ever) suggested that finding this particular isotope (iron-60) in the fossil record could tell researchers when exactly supernovae occurred over the eons in Earth’s history. That’s because iron-60 is radioactive; it eventually decays into cobalt and then nickel over eons.

What this means is that, if any iron-60 atoms formed together with our planet, then it would have long ago metamorphosized into another element. So if iron-60 atoms are present on Earth, then it probably got here from interstellar space — specifically from the dead remnant of an exploding star, a supernova — studying more iron-60 could help us find out when that supernova occurred.

 

Whence Cometh Iron-60?

In 2016, two papers were published on Nature suggesting this very same isotope (iron-60) as evidence of such an ancient supernova. The first paper was from a team of scientists in Australia, who found evidence of iron-60 isotopes in an ancient seabed, and were able to successfully trace their origin to that of supernovae that occurred roughly from 325 lightyears away. The other paper was from a team of scientists in Germany, and were also able to figure out precisely, the time these supernovae occurred — roughly 2 million years ago, and the other, roughly 7 million years ago, respectively.

Moreover, for a supernova to have serious effects on our planet, it has to be in the “kill zone” of at least 30 lightyears away before that explosion could be a real threat to life on Earth. So the scientists noticed that 325 lightyears is really far away, but not so far away that iron-60 couldn’t make an interstellar trip to Earth. However, according to yet again another paper by the University of Kansas, these far-to-reach supernovae could have done the same amount of damage despite that it reached the Earth at a very lesser instantaneous pace.

“I’ve been doing research like this for about 15 years, and always in the past it’s been based on what we know generally about the universe — that these supernovae should have affected Earth at some time or another,” Adrian Melott, an astrophysicist at the University of Kansas, and the team’s led author, said in a statement.

“This time, it’s different. 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 — it’s much more specific.”

 

The Interstellar Atrocities

First and foremost, the research team provided ample evidence for the occurrence of such ancient supernovae in the form of the Local Bubble — a hollowed-out space that comprises of interstellar gas and dust, debris, and cosmic rays found between stars also known as the interstellar medium.

In the event of a supernova, a star tears itself in the most violent event you could ever imagine. As a result, it totally wipes out almost all of the gas and dust in it’s range, which creates a “bubble.” But when multiple stars explode next to each other, those bubbles get (you guessed it) combined. (Now, you just take a second to imagine what a multiple number of supernovae would look like). That’s exactly what our Local Bubble looks like, and that’s what these scientists thought might have occurred — the idea of multiple supernovae, let’s call that a “multinova.”

But here’s the real catch: How on Earth in the amazing world of science does a “multinova” explain what caused the mass extinction of all marine megafauna — like the megalodon, a species of shark that was the size of a school bus — at the end of the Pleistocene? Hmmm!

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So What’s Really The Culprit?

In order to explain all this, the scientists at last pushed the blame on the muon — a subatomic particle a few hundred times more massive than that of an electron. These heavily dense yet whatever in the nano name of the quantum world, hit the surface of the Earth most often. They get here via auroras from interstellar space that coincide with our atmosphere. You have muons passing through you all the time — they’re just sparse enough not to cause any real damage.

“Nearly all of them pass through harmlessly, yet about one-fifth of our radiation dose comes by muons,” says Melott. “But when this wave of cosmic rays hits, multiply those muons by a few hundred. Only a small fraction 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.”

Finally, the scientists made an estimate in comparison with the size of a human, the muons would trigger cancer rates up to roughly 50 percent; and the bigger the animal size, the worse that rate gets. The Pleistocene extinction event decimated about 36 percent of genera — plural for genus, the organism classification above species — most of which were in coastal areas where large surface-dwelling marine animals lived. The muons couldn’t have done as much damage as in deeper waters, but they could still reach hundreds of meters down. Although the damage wouldn’t have been as quick as an asteroid impact or a volcanic eruption, yet it definitely could have happened.

“There really hasn’t been any good explanation for the marine megafaunal extinction,” Melott said. “[and] This could be one.”

 

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Written by: Nana Kwadwo, Fri, Mar 08, 2019.

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