A new study carried out by scientists at the University of Illinois (USA) and published in the journal PNAS, concludes that 359 million years ago, the explosion of a supernova would have caused a mass extinction on Earth, which caused the collapse of the ozone layer and a warming that made 83% of the species disappear.
This great destroyer of life on Earth could have been a strange and distant phenomenon: a dying star, exploding across the galaxy, many light years away from our own remote planet. This supernova would therefore have caused a mass extinction event during the late Devonian period that would have nothing to do with terrestrial causes such as a volcanic eruption. The experts found radioactive isotopes in rocks that could confirm such an event.
Geological era: Devonian
During the late Devonian period (which ended about 354 million years ago), when most of life was found in the oceans, one of the worst mass extinctions in Earth’s history severely damaged its ecosystem. However, we have never been entirely clear what caused it.
To explain the event, the researchers looked at rocks with prehistoric plant spores . These spores appeared to have been severely burned by ultraviolet light, probably as a consequence of a prolonged lack of ozone in the atmosphere.
“Terrestrial catastrophes, such as large-scale volcanism and global warming, can also destroy the ozone layer, but the evidence for this is not conclusive for the time interval in question,” commented Brian Fields, leader of the paper. “Instead, we propose that one or more supernova explosions, some 65 light-years distant from Earth, could have been responsible for the prolonged ozone loss.”
There is no doubt that this macro-event would have illuminated the skies in an impressive way.
“Supernovae (SNe) are fast sources of ionizing photons: ultraviolet rays, X-rays and extreme gamma rays,” explain the authors and their cosmic rays could be strong enough to deplete the ozone layer and cause radiation damage. long-lived life forms within the Earth’s biosphere.
“To put this in perspective, one of the closest supernova threats today is the star Betelgeuse, which is more than 600 light years away and well beyond the 25 light-year death distance,” he clarified. Adrienne Ertel, co-author of the study.
The team also looked at other causes of ozone depletion, including meteorite impacts and gamma-ray bursts, but none of these factors would have caused long-term depletion.
Thus, this hypothesis, since we do not have any evidence that can confirm such an extreme, suggests that the violent supernova flooded our planet with dangerous UV, X and gamma rays, irradiating the ozone layer with effects that would have lasted up to 100,000 years, according to researchers. To confirm their suspicions, the team is now searching for the “smoking gun”: two specific radioactive isotopes of plutonium, originating in the late Devonian period, that could only have reached Earth from cosmic explosions: plutonium-244 and samarium-146.
“The overall message from our study is that life on Earth does not exist in isolation,” Fields explains . “We are citizens of a larger cosmos, and the cosmos intervenes in our lives, often imperceptibly, but sometimes fiercely.”
Referencia: Brian D. Fields, Adrian L. Melott, John Ellis, Adrienne F. Ertel, Brian J. Fry, Bruce S. Lieberman, Zhenghai Liu, Jesse A. Miller, Brian C. Thomas. Supernova triggers for end-Devonian extinctions. Proceedings of the National Academy of Sciences, 2020; 202013774 DOI: 10.1073/pnas.2013774117
