Ancient supernovae buffeted Earth's biology with radiation dose, researcher says

Supernova
This image shows the remnant of Supernova 1987A seen in light of very different wavelengths. ALMA data (in red) shows newly formed dust in the centre of the remnant. Hubble (in green) and Chandra (in blue) data show the expanding shock wave. Credit: ALMA/NASA

Research published in April provided "slam dunk" evidence of two prehistoric supernovae exploding about 300 light years from Earth. Now, a follow-up investigation based on computer modeling shows those supernovae likely exposed biology on our planet to a long-lasting gust of cosmic radiation, which also affected the atmosphere.

"I was surprised to see as much effect as there was," said Adrian Melott, professor of physics at the University of Kansas, who co-authored the new paper appearing The Astrophysical Journal Letters, a peer-reviewed express scientific journal that allows astrophysicists to rapidly publish short notices of significant original research.

"I was expecting there to be very little effect at all," he said. "The supernovae were pretty far way—more than 300 light years—that's really not very close."

According to Melott, initially the two stars that exploded 1.7 to 3.2 million and 6.5 to 8.7 million years ago each would have caused blue light in the night sky brilliant enough to disrupt animals' sleep patterns for a few weeks.

But their major effect would have come from radiation, which the KU astrophysicist said would have packed doses equivalent to one CT scan per year for every creature inhabiting land or shallower parts of the ocean.

"The big thing turns out to be the ," Melott said. "The really high-energy ones are pretty rare. They get increased by quite a lot here—for a few hundred to thousands of years, by a factor of a few hundred. The are the ones that can penetrate the atmosphere. They tear up molecules, they can rip electrons off atoms, and that goes on right down to the ground level. Normally that happens only at high altitude."

Melott's collaborators on the research are Brian Thomas and Emily Engler of Washburn University, Michael Kachelrieß of the Institutt for fysikk in Norway, Andrew Overholt of MidAmerica Nazarene University and Dimitry Semikoz of the Observatoire de Paris and Moscow Engineering Physics Institute.

The boosted exposure to cosmic rays from supernovae could have had "substantial effects on the terrestrial atmosphere and biota," the authors write.

For instance, the research suggested the supernovae might have caused a 20-fold increase in irradiation by muons at ground level on Earth.

"A muon is a cousin of the electron, a couple of hundred times heavier than the electron—they penetrate hundreds of meters of rock," Melott said. "Normally there are lots of them hitting us on the ground. They mostly just go through us, but because of their large numbers contribute about 1/6 of our normal radiation dose. So if there were 20 times as many, you're in the ballpark of tripling the radiation dose."

Melott said the uptick in radiation from muons would have been high enough to boost the mutation rate and frequency of cancer, "but not enormously. Still, if you increased the you might speed up evolution."

Indeed, a minor mass extinction around 2.59 million years ago may be connected in part to boosted cosmic rays that could have helped to cool Earth's climate. The new research results show that the cosmic rays ionize the Earth's atmosphere in the troposphere—the lowest level of the atmosphere—to a level eight times higher than normal. This would have caused an increase in cloud-to-ground lightning.

"There was climate change around this time," Melott said. "Africa dried out, and a lot of the forest turned into savannah. Around this time and afterwards, we started having glaciations—ice ages—over and over again, and it's not clear why that started to happen. It's controversial, but maybe cosmic rays had something to do with it."


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Journal information: Astrophysical Journal Letters

Citation: Ancient supernovae buffeted Earth's biology with radiation dose, researcher says (2016, July 11) retrieved 22 July 2019 from https://phys.org/news/2016-07-ancient-supernovae-buffeted-earth-biology.html
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Jul 11, 2016
2 million years ago the Amazon rain forest was pampas, steppes, grasslands. The planet didn't die in that climate change and human produced CO2 is no supernova equivalent.

The climate changes, it's what chaotic systems do.

Jul 11, 2016
"I was expecting there to be very little effect at all," he said. "The supernovae were pretty far way—more than 300 light years—that's really not very close."

Yes, the expectations of astronomers keep them in the dark about the big problem: the cosmic ray superwave periodically emanating from the galactic core. The last rather minor wave likely caused the last ice age and is now illuminating the Crab Nebula.

Jul 11, 2016
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Jul 11, 2016
The inmates have officially taken over the asylum.

Jul 11, 2016
Note that cat-astro-phe means "falling (cata-) star (-astro)", and dis-aster can also be interpreted in a similar manner as tracing back to "bad (dus-) star (-aster)".

False equivalency. First, human language wasn't around to describe anything when these supernovae made their purported impact on Earth. Secondly, it was only when astrology came into general practice as an attempt to attribute events on Earth with the "Heavens" that such ideas took root. Of course, we know now that astrology is nothing more than a steaming pile of irrational hooey.

Jul 11, 2016
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Jul 11, 2016
. First, human language wasn't around to describe anything when these supernovae made their purported impact on Earth.

But maybe... It caused the mutations that evolved into the ability to generate language... All that electricity in the air...:-)

Jul 11, 2016
Note that cat-astro-phe means "falling (cata-) star (-astro)", and dis-aster can also be interpreted in a similar manner as tracing back to "bad (dus-) star (-aster)".

Actually, no. May I suggest you look online for etymologies before making such statements? (It's not that hard...)
In this case, multiple reputable references state the derivation to be (paraphrasing for brevity):
From Greek katastrophē, from kata = "down" and strephein = "turn" and subsequently Latin catastropha, a "reversal of what is expected". Nothing whatsoever to do with stars, falling or otherwise. In modern usage as meaning a sudden disaster the word is apparently first recorded in 1748.

Jul 11, 2016
In addition, while "disaster" is indeed a reference to stars or planets, it is astrological in terms of a position of a star or planet in one's zodiacal horoscope causing a malign influence. The "dis" part is perjorative (ill or bad) but taken from Greek and Latin "dis" and later Middle English and French "des". (In effect "bad luck from the stars' influence".)

Jul 11, 2016
Note that cat-astro-phe means "falling (cata-) star (-astro)"

No, it's from kata (down) strophe (turning).
edit: I see that malapropism beat me to it!

Jul 12, 2016
2 million years ago the Amazon rain forest was pampas, steppes, grasslands. The planet didn't die in that climate change and human produced CO2 is no supernova equivalent.

The climate changes, it's what chaotic systems do.

And yet there was a minor mass extinction event at the same time.

Nice strawman by the way. No one says the world would die, dummy, it is that many species will be unable to adapt in time to avoid extinction.

Climate change is caused by something you stupid old twit. In the case of today, it is caused by humans putting gigatonnes of CO2 into the air every year.

Clearly, you know about the same of climate or climate science as Freeman Dyson. At lease he admits it. .

Why do you even bother?

Jul 12, 2016
"There was climate change around this time," Melott said. "Africa dried out, and a lot of the forest turned into savannah.


So, under the savannah hypothesis, these supernovas are the main factor responsible for the evolution of hominins.

The climate changes, it's what chaotic systems do.


"The mass extinction rate changes, it's what chaotic systems do."

Yes, but now the climate change is known to 99.9 % certainty to be caused by our society (mainly CO2 release) by the latest review.

It is also suspected that the attendant mass extinction has the same driving force.

But the point is that not only are we responsible, we can change the outcome. It is now also the economical choice as far as I know from the press releases, since from now on climate change and extinctions will cost us more than preventing them.

What are we waiting for? Not the climate science deniers, obviously! They have no sensible position in this.

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