Several supernova explosions about 65 light-years away may have contributed to the ozone depletion and several subsequent extinctions at the Devonian-Carboniferous border, about 359 million years ago, according to a new paper published in the Procedures of the National Academy of Sciences.
A rendering of an artist from a supernova explosion. Image credit: ESA / Hubble / L. Calcada / NASA’s Goddard Space Flight Center.
Devonian-Carboniferous boundary rock samples contain deformed plant spores that appear to be sunburned by ultraviolet light – evidence of an event with long-lasting ozone.
“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 Professor Brian Fields, a researcher in the Department of Ecology & Evolutionary Biology and the Biodiversity Institute at the University of Kansas.
“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.”
Professor Fields and colleagues investigated various astrophysical causes for this ozone depletion, such as meteorite impact, solar flares and gamma-ray bursts.
“But these events end quickly and are likely to cause the long-term ozone depletion that occurred at the end of the Devonian period,” said Jesse Miller, a student at the Illinois Center for Advanced Studies of the Universe and the Department of Astronomy. the University of Illinois.
A supernova, on the other hand, delivers a one-two punch: it bathes Earth instantly with damaging UV, X-rays and gamma rays; later, supernova punches strike the solar system, subjecting the planet to long-lived radiation from cosmic rays, accelerated by the supernova. The damage to Earth and its ozone layer can last up to 100,000 years.
But fossil evidence points to a 300,000-year decline in biodiversity leading to the extinction of Devonian-Carboniferous, suggesting the possibility of multiple disasters, perhaps even multiple supernova explosions.
“It is entirely possible. “Mass stars usually occur in clusters with other massive stars, and other supernovae are likely to occur soon after the first explosion,” Miller said.
The key to proving that a supernova happened would be to find the radioactive isotopes plutonium-244 and samarium-146 in the rocks and fossils that were deposited at the time of extinction.
“None of these isotopes occur naturally on Earth today, and the only way they can get here is through cosmic explosions,” said Zhenghai Liu, an undergraduate student at the Illinois Center for Advanced Studies of the Universe and the Department. astronomy at the University of Illinois.
“Plutonium-244 and samarium-146 decay over time,” Professor Fields said.
“So when we find the radioisotopes on Earth today, we know that they are fresh and not from and therefore the smoke guns of a nearby supernova.”
Scientists have yet to find plutonium-244 and samarium-146 in Devonian-Carboniferous boundary rocks.
“The overwhelming message of our study is that life on earth does not exist in isolation,” Professor Fields said.
“We are citizens of a larger cosmos, and the cosmos intervenes in our lives – often imperceptibly, but sometimes cruelly.”
_____
Brian D. Fields and others. Supernova triggers for end-Devonian extinctions. PNAS, published online August 18, 2020; doi: 10.1073 / pnas.2013774117
