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One of the worst extinction events in Earth history may have been triggered by a supernova, the violent death of a distant star.
About 75% of all species on Earth have died by the end of the Devonian period, almost 360 million years ago. Rocks from this era retain several thousand spores that appear to be scorched by ultraviolet (UV) rays, indicating that something has gone wrong with our protective ozone layer.
The destructive force can come from far away, suggests a new study.
Related: Stunning images of supernova explosions
“Earth-based disasters such as large-scale volcanism and global warming can also destroy the ozone layer, but the evidence for these is inconclusive for the time interval in question,” lead author Brian Fields, professor of physics and astronomy at the University of Illinois, Urbana-Champaign, said in a press release.
“Instead, we suggest that one or more supernova explosions, about 65 light years from Earth, could have been responsible for the prolonged loss of ozone, ”Fields said.
“To put this in perspective: one of the closest supernova threats today comes from the star Betelgeuse, which is over 600 light years away and well outside the destruction distance of 25 light years, ”said co-author Adrienne Ertel, a graduate student of the Fields research group, in the same release.
Death by an exploding star?
Supernovas, which end the life of giant stars like Betelgeuse, can strike life on Earth with a powerful double punch. Highly energetic UV, X and gamma rays deliver the first sharp blow and the second comes from swarms of charged particles called cosmic rays which are accelerated to tremendous speeds by the explosion. This combo can damage the earth’s ozone layer for about 100,000 years, study team members said.
Fossil evidence suggests that biodiversity declined dramatically for about 300,000 years at the end of the Devonian, often referred to as the “Age of Fish” due to its great diversity of fish. So, the Late Devonian extinction may have involved several different dramatic events – perhaps two or more nearby supernova explosions.
“It’s entirely possible,” said study co-author Jesse Miller, another graduate student from Fields’ lab. “Massive stars generally occur in clusters with other massive stars, and other supernovae are likely to occur soon after the first explosion.”
The researchers suggested a way to test their hypothesis: to look for the radioactive isotopes plutonium-244 and samarium-146 in rocks and fossils from the Late Devonian period. (Isotopes are versions of chemical elements with different numbers of neutrons in their nuclei.)
“None of these isotopes occur naturally on Earth today, and the only way to get there is through cosmic explosions,” said study co-author Zhenghai Liu, an undergraduate student at the ‘University of Illinois at Urbana-Champaign, in the same release. .
Such research has yet to take place, study team members said.
Supernova vs. Earth
Fields and his team aren’t the first researchers to find possible links between supernovas and extinction events. For example, another group recently proposed that a supernova contributed to minor mass extinction at the end of the Pliocene era, about 2.6 million years ago.
Such ideas are not exactly beyond, given that we already have a documented case of dramatic death from above. The mass extinction at the end of the Cretaceous 66 million years ago, which was done for non-avian dinosaurs, was probably triggered when a comet or asteroid about 10 kilometers wide slammed on Earth.
“The main 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 fiercely.”
The events of the Late Devonian and the Late Cretaceous are two of the five mass extinctions that scientists have traditionally recognized. However, there is a growing consensus that we are now living sixth mass extinction – one caused mainly by humanity, global warming and habitat destruction being two of the main factors.
the new study was published online Tuesday (August 18) in Proceedings of the National Academy of Sciences.
Mike Wall is the author of “Out There” (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for extraterrestrial life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
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