A new paper in the Proceedings of the National Academy of Sciences theorizes that cosmic rays from supernovae may be responsible for at least one mass extinction event.

The event in question occurred between the Devonian and Carboniferous periods around 359 million years ago. Rocks dated to this time contain numerous plant spores that show evidence of long-lasting ozone depletion. While more terrestrial events could lead to that type of ozone catastrophe, the evidence for those is inconclusive at best. The researchers proposed that a supernova, or possibly more than one, from about 65 million light-years away, is the real culprit.

According to the article: A supernova…delivers a one-two punch. The explosion immediately bathes Earth with damaging UV, X-rays, and gamma rays. Later, the blast of supernova debris slams into the solar system, subjecting the planet to long-lived irradiation from cosmic rays accelerated by the supernova. The damage to Earth and its ozone layer can last for up to 100,000 years. However, fossil evidence indicates a 300,000-year decline in biodiversity leading up to the Devonian-Carboniferous mass extinction, suggesting the possibility of multiple catastrophes, maybe even multiple supernovae explosions.

To prove their theory, the team hopes to find a couple of radioactive isotopes — plutonium-244 and samarium-146 — in the rocks and fossils of the time period. Since these isotopes do not occur naturally on Earth, they had to have come from space in a cosmic explosion.

Lead author Brian Fields explains that these isotopes are like green bananas: When you see green bananas in Illinois, you know they are fresh, and you know they did not grow here. Like bananas, Pu-244 and Sm-146 decay over time. So if we find these radioisotopes on Earth today, we know they are fresh and not from here – the green bananas of the isotope world – and thus the smoking guns of a nearby supernova.

We here at CosmoQuest wish the team luck in their search for these isotopes. I’m honestly pretty excited to see where this story goes.

More Information

University of Illinois, Urbana-Champaign press release 

“Supernova Triggers for End-Devonian Extinctions,” Brian D. Fields et al., 2020 Aug. 18, Proceedings of the National Academy of Sciences