Earlier this spring, astronomers used telltale evidence in seafloor sediments and moon-dust to study two nearby supernovae that blew up a few hundred light years away. One exploded between 1.5 and 3.2 million years ago and the other 6.5 to 8.7 million years ago.

Adrian Melott, a physicist at the University of Kansas, wondered about the timing of the more recent supernova. Its date range includes the timeline of a minor extinction event at the endstart of the Pleistocene, about 2.59 million years ago, one that was long thought to be caused, in part, by a cooling climate and dramatic regional changes in Africa and central America. Melott and others had wondered whether a supernova could shower enough particles and radiation on Earth to cause mass extinctions. Thanks to the new research on supernova history, they could now look into it in earnest.

Melott ran computer simulations that suggested that even mild star-explosions would shower Earth with radiation for hundreds of thousands of years, provided they were local. They would also ionize the atmosphere to a level eight times higher than normal, which would trigger an increase in cloud-to-ground lightning.

“I really expected to conclude that there wasn’t much chance of an effect, because of the distance, but it turned out to be more substantial than I expected,” Melott says.

While Melott and his coauthors were working on this paper, which appears today in The Astrophysical Journal Letters, another supernova archaeology team was refining the most recent research on the two local supernovae from 1.5 and 3.2 million and 6.5 to 8.7 million years ago. Brian Fields, Brian Fry and John Ellis argue that those supernovae were closer than scientists thought — maybe only 150 light years distant, not 325. If that’s true, the radiation effect would be even stronger, Melott says.

The immediate radiation dose wouldn’t be terrible, roughly comparable to the amount you’d receive in a CT scan. But it wouldn’t be a one-shot deal. Instead, the radiation would rain down for hundreds of thousands of years. Melott says the particles would largely include muons, which are a sister particle of the electron and have more energy, so they can penetrate deeper, including into the oceans. They would also add up to a bigger effect on large animals, like mammoths, maybe, or humans. All told, supernova radiation could triple the everyday background radiation from cosmic rays.

“It would trivially increase your chances of cancer, but if you do it to every organism on Earth, for hundreds of thousands of years, there might be something you could see,” Melott says. “If you could have good enough statistics to look for bone cancer in fossils, for instance, you might be able to do that.” Melott said he had worked on research into whether this was actually possible.