A flood of high-energy radiation and cosmic rays from one or more nearby supernova blasts may have triggered at least one of Earth’s mass extinctions, researchers say, wrecking the planet’s protective ozone layer for an extended period some 359 million years ago
“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 Brian Fields, an astronomy and physics professor at the University of Illinois, Urbana-Champaign.
“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 research is outlined in the Proceedings of the National Academy of Sciences.
Fields and his students focused on the boundary between the Devonian and Carboniferous periods where hundreds of thousands of generations of plant spores appear to be damaged, or sunburnt, by ultraviolet light, an indication of a damaged ozone layer that may have persisted for several hundred thousand years.
The researchers considered a variety of explanations, ranging from large asteroid impacts impacts to solar flares and gamma ray bursts, “but these events end quickly and are unlikely to cause the long-lasting ozone depletion that happened at the end of the Devonian period,” said graduate student and study co-author Jesse Miller.
But a supernova would have delivered a one-two punch, bathing Earth in high energy ultraviolet radiation, X-rays and gamma rays followed by debris slamming into the solar system, compressing the heliosphere and subjecting Earth to long-lived radiation from cosmic rays. Damage to the planet’s ozone layer could have persisted for up to 100,000 years.
The fossil record indicates a 300,000-year decline in biodiversity preceding the mass extinction. But Miller said multiple catastrophes, including more than one supernova event, are “entirely possible.”
“Massive stars usually occur in clusters with other massive stars, and other supernovae are likely to occur soon after the first explosion,” he said.
One way to prove a nearby supernova occurred is to look for radioactive isotopes of plutonium-244 and samarium-146 in rocks found near the boundary between the Devonian and Carboniferous periods. Neither isotope occurs naturally on Earth today and, if present, they would represent “the smoking guns of a nearby supernova,” Fields said.