Scientists just found ash from a supernova in bacteria fossils, suggesting an exploding star may have been responsible for an extinction event millions of years ago.
When a star goes supernova, its core collapses. Then it explodes and ejects a huge cloud of the radioactive isotope iron 60. There is no natural way to get iron 60 on Earth, according to the research.
Previously, scientists have found evidence of supernova dust in ocean sediment. Now researchers have taken a closer look at that sediment and discovered iron 60 inside tiny fossils of magnetotactic bacteria.
The fossils first appeared about 2.6 million to 2.8 million years ago. Our solar system spent close to one million years passing through the could of supernova debris, according to study co-author Shawn Bishop.
This supernova rain happened around the same time a big extinction event wiped out several types of mollusks on Earth, according to the research. The scientists can't say for sure whether the supernova triggered this extinction, but the evidence seems to suggest it.
It's also puzzling that the Earth took so long to travel through the supernova debris, since an exploding star sends material flying initially at millions of miles per hour.
"There's a mystery there," Bishop told Business Insider. "Can the ejecta from a supernova explosion be spread out in time? This is something that needs to be explained and understood."