One of the worst extinction events in the history of the earth may have been triggered by a supernova, the violent death of a distant star.
About 75% of all species on Earth died at the end of the Devonian period, almost 360 million years ago. Stones from this era retain many thousands of traces that appear to be burned by ultraviolet (UV) radiation, indicating that something seriously went wrong with our protective ozone layer.
The destructive power may have come from very far away, a new study suggests.
Related: Great images of supernova explosions
“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,” leads author Brian Fields, a professor of physics and astronomy at the University of Illinois, Urbana. Champaign, said in a statement.
“Instead, we represent that one or more supernova explosions, about 65 light-years away from Earth, could have been responsible for the prolonged loss of ozone, “Fields said.
“To put this in perspective: One of the closest threats to supernovae today is from the star Betelgeuse, which is more than 600 light-years away and well beyond the kill distance of 25 light-years, “said co-author Adrienne Ertel, a graduate student in the Fields research group, in the same statement.
Dying by exploding star?
Supernovae, which end the life of giant stars like Betelgeuse, can hit Earthly life with a powerful one-two punch. High energy UV, X-rays and gamma rays provide the first wallop, and the second comes from swarms of charged particles called cosmic rays which are accelerated by the explosion to enormous speeds. This combo could damage the Earth’s ozone layer for 100,000 years or so, student team members said.
Fossil evidence suggests that biodiversity declined substantially at the end of the Devonian some 300,000 years ago, which is often referred to as “The Age of Fishes” because of its vast fish diversity. That late Devonian extinction may have involved several different dramatic events – perhaps two or more near-supernova explosions.
“This is entirely possible,” said study author Jesse Miller, another graduate student in Fields’ lab. “Massive stars normally occur in clusters with other massive stars, and other supernovae are likely to occur shortly after the first explosion.”
The researchers suggested a way to test their hypothesis: 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 they can get here is through cosmic explosions,” studied co-author Zhenghai Liu, an undergraduate student at the University of Illinois at Urbana-Champaign. , said in the same statement.
Such a search has not yet happened, student team members said.
Supernova vs. earth
Fields and his team are not the first researchers to find possible links between supernovae and extinction events. For example, another group recently suggested that a supernova contributed to the small mass extinction at the end of the Pliocene period, about 2.6 million years ago.
Such ideas are not exactly outrageous, 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 became famous in the non-avian dinosaurs, was probably triggered when a comet or asteroid about 6 miles (10 kilometers) wide slaughtered in Earth.
“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.”
The Late Devonian and Late Cretaceous events are two of the five mass extinctions that scientists have long recognized. However, there is a growing consensus that we are now living through a sixth mass extinction – one caused primarily by humanity, with global warming and habitat destruction two of the biggest drivers.
De new research was published online Tuesday (Aug. 18) in the 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 alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
