Several global extinction events occurred during the Devonian period, which lasted from 359 million to 419.2 million years ago, and it also ended. The collective events resulted in the loss of 70 to 80 percent of all animal species present during the Devonian, for the most part affecting marine life.
The beginning of the Carboniferous period, occurred after, and lasted between 299 million to 359.2 million years ago.
No single cause has previously been associated with Devonian extinctions, but new research suggests that multiple supernovae may have caused the decline in ozone levels with the definitive extinction event that ended the Devonian period.
The research team focused on the boundary between the Devonian and Carboniferous periods, because rocks from this time reveal something intriguing. The plant spores contained in it appear to have been burned by ultraviolet light. Ozone levels in the Earth’s stratosphere are also falling at this time.
“Earth-based disasters such as large-scale volcanism and global warming can also destroy the ozone layer, but evidence for this is not one-sided for the time interval in question,” said Brian Fields, author of the study and University of Illinois at Urbana-Champaign astronomy and physics professor, in a statement.
“Instead, we suggest that one or more supernova explosions, about 65 light-years away from Earth, could have been responsible for the prolonged loss of ozone.”
The “kill distance” for supernovae is about 25 light-years away. A supernova, like multiple explosions, from 65 light-years away would not diminish life on Earth, but it could hit our planet with enough radiation to damage the ozone layer and expose Earth to ultraviolet rays and cosmic rays.
In striking distance
Gamma-ray bursts, solar flares and the impact of meteorites hitting Earth could also extract ozone, but they do not seem likely in this case.
“But these events are ending rapidly and are likely to cause the prolonged ozone depletion that occurred at the end of the Devonian period,” said Jesse Miller, study co-founder and University of Illinois at Urbana-Champaign student, in a statement.
An exploding star, like multiple exploding stars, would immediately cause damage by hitting Earth with UV, gamma and X-rays. And about a thousand years later, the actual supernova puddle would hit our solar system, radiating Earth with high levels of intense cosmic rays.
This type of damage could last 100,000 years, according to Adrian L. Melott, study co-author and physicist at the University of Kansas.
“The cosmic rays of such a supernova will produce moons in the atmosphere, which are a very penetrating type of radiation, “Melott said. They could cause internal damage in large animals and in organisms up to half a mile in the ocean. “
There was also likely to be an excess of lightning, which could cause wildfires and lead to climate change.
Following the event of mass extinction 359 million years ago, evidence in the fossil record suggests that the Earth’s biodiversity has been declining for more than 300,000 years – the other events for extinction of the Devonian period.
This is why scientists believe that multiple supernovae are responsible for what happened on Earth, which is very likely.
“Very massive stars are typically born in large associations, and they live short lives, so they will probably go away at the same time,” Melott said.
Proving that supernovae were the cause of these mass extinctions will find radioactive isotopes in the rock record from this time period, such as plutonium-244 and samarium-146. Supernovae would have found traces of these in rocks and fossils on Earth.
“None of these isotopes occur naturally on Earth today, and the only way they can get here is through cosmic explosions,” Zhenghai Liu, study co-author and University of Illinois, Urbana-Champaign student, said in a statement.
“When you see green bananas in Illinois, you know they’re fresh, and you know they’ve not grown here,” Fields said. “Like bananas decay in the time Pu-244 and Sm-146. So when we find the radioisotopes on Earth today, we know that they are fresh and not from here – the green bananas of the isotope world – and thus the smoke guns of a near supernova. “
“For more than a decade, my colleagues and I have been interested in the possibility of ionizing radiation events that cause extinction events on Earth,” Melott said.
“The overwhelming message of our study is that life on earth does not exist in isolation,” Fields said. “We are citizens of a larger cosmos, and the cosmos intervenes in our lives – often imperceptibly, but sometimes cruelly.”
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