|Can a supernova explain an ancient mass extinction?|
This study suggests that cosmic rays from a nearby supernova triggered a mass extinction. New research explores whether astronomical phenomena were responsible for a large-scale extinction event 359 million years ago, at the boundary between the Devonian and Carboniferous periods.
Supernova mass extinctionThe study led by Brian Fields, professor of astronomy and physics at the University of Illinois, Urbana-Champaign. And published in Proceedings of the National Academy of Sciences, suggests that cosmic rays from a nearby supernova triggered that extinction. Certain radioactive isotopes in the Earth's rock record could confirm this scenario.
The team focused on the Devonian-Carboniferous boundary.Those rocks contain hundreds of thousands of generations of plant spores that appear to have been burned by ultraviolet light. Evidence of a long-lasting ozone depletion event.
Earth-based disasters, 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 frame in question," Fields said.Instead, we propose that one or more supernova explosions, about 65 light-years away from Earth, could have been responsible for the prolonged loss of ozone.
To put this in perspective, one of the closest supernova threats today is the star Betelgeuse, which is more than 600 light-years away.
Well beyond the death distance of 25 light-years," graduate student and study co-author Adrienne Ertel said in a statement.
The team explored other astrophysical causes of ozone depletion.Such as meteorite impacts, solar flares, and gamma-ray bursts.
"But these events end quickly and are unlikely to cause the lasting ozone depletion that occurred at the end of the Devonian period," said graduate student and study co-author Jesse Miller.A supernova, on the other hand, strikes a double blow, researchers said. The explosion bathes the Earth in harmful ultraviolet, X-ray, and gamma rays. Later, the supernova debris explosion hits the solar system, subjecting the planet to long-lasting radiation of cosmic rays accelerated by the supernova. The damage to the Earth and its ozone layer can last for up to 100,000 years.
However, fossil evidence indicates a 300,000-year decline in biodiversity that led to the Devonian-Carboniferous mass extinction. Suggesting the possibility of multiple catastrophes, even numerous supernova explosions.
Supernova mass extinction is entirely possible.Massive stars usually occur in clusters with other massive stars, and other supernovae are likely to occur shortly after the first explosion.
The team said the key to proving that a supernova occurred would be to find the radioactive isotopes plutonium-244 and samarium-146 in the rocks and fossils deposited at the time of the extinction.
None of these isotopes are naturally found on Earth today. The only way they can get here is through cosmic explosions," said undergraduate student and co-author Zhenghai Liu.
Supernova-born radioactive species are like green bananas," Fields said.When you see green bananas in Illinois, you know they're fresh and didn't grow here. Like bananas, Pu-244 and Sm-146 decompose over time. So, if we find these radioisotopes on Earth today, we will know they are fresh and not from here, the green bananas of the isotope world. And, therefore, the smoking guns of a nearby supernova.
Researchers mention that the species that inhabited the Earth at that time did not die from radiation but from a lack of ozone that could result from different reasons:
- Meteorite impacts.
- Solar flares.
- Gamma-ray bursts.
To thoroughly test this theory, researchers have to find the radioactive isotopes plutonium-244 and samarium-146 in the rocks and fossils from the explosion. But none are currently found naturally on Earth and could only be reached through cosmic blasts.