Researchers still need to find evidence to confirm whether this astronomical event would have affected our planet.
A study led by the University of Illinois, USA, suggests that exploding stars may have been responsible for the mass extinction that occurred 359 million years ago, marking the end of the Devonian period and the beginning of the Carboniferous.
Recently published in the Proceedings of the National Academy of Sciences, the article explores the possibility that harmful cosmic rays emitted by supernovae close to Earth may have affected the planet’s habitability.
To confirm this theory, researchers need to find radioactive isotopes in rocks from that period, such as plutonium-244 (Pu-244) and samarium-146 (Sm-146).
“Neither of these isotopes occurs naturally on Earth today, and the only way they can get here is via cosmic explosions,” explained researcher Zhenghai Liu, co-author of the study.
The scientists decided to focus on the Devonian-Carboniferous mass extinction because there are several fossil records of plant spores that appear to have been burned by ultraviolet light, indicating a long-lasting ozone-depletion event.
“Earth-based catastrophes such as large-scale volcanism and global warming can destroy the ozone layer, too, but evidence for those is inconclusive for the time interval in question,” said physics professor and study leader Brian Fields, from the University of Illinois. “Instead, we propose that one or more supernova explosions, about 65 light-years away from Earth, could have been responsible for the protracted loss of ozone.”
The researchers also took into account other astronomical events that can deplete ozone, such as meteorite impacts, solar eruptions, and gamma-ray bursts, but concluded that they do not last long enough to cause a mass extinction on the planet.
The explosion of a supernova, on the other hand, could be quite devastating. That’s because it would immediately bathe the Earth with harmful X-rays, ultraviolet light, and gamma-rays.
Debris from the supernova would also hit the Solar System, exposing the planet to long-lived irradiation from cosmic rays. The damage caused to the Earth and its ozone layer could last up to 100,000 years.
Currently, there are no imminent supernova threats near the Solar System. If Betelgeuse exploded in a supernova, for example, its kill distance would only reach 25 light-years away, while the star is 600 light-years from Earth.
Researchers still need to look for Pu-244 or Sm-146 in rocks dating from the Devonian-Carboniferous boundary to prove their theory. Fields’ team said their study aims to define evidence patterns in the geological record that would point to supernova explosions.
“The overarching 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 ferociously.”