For years, researchers have puzzled over evidence that a supernova exploded somewhere in Earth’s vicinity a couple million years ago. The evidence is a concentration of 60Fe, an isotope of iron produced by supernovae, found around the Earth.
Now, a new study presents additional evidence of a supernova explosion near Earth 2.5 million years ago. This time, its a concentration of 53Mn, another radioisotope produced by supernovae.
The study presenting the findings is titled “Supernova-Produced 53Mn on Earth.” The lead author of the paper is Dr. Gunther Korschinek from the Technical University of Munich.
The study is centered on what are called Ferromanganese crusts. They’re made of rock, but look more like chocolate cake. They’re deposits of marine sediments that grow over time, as iron and manganese oxides precipitate out of the seawater. They keep a record of the chemicals in the source water as they form over time. Besides being a potential source of valuable minerals, they’re also valuable evidence for scientists. The team of researchers behind this study examined samples of these ferromanganese crusts and found not only 60Fe, but also 53Mn.
The 60Fe found on the Earth is potential evidence of a supernova explosion in Earth’s rough vicinity. 60Fe is known as an extinct radionuclide. Because its half life is 2.6 million years, any 60Fe on Earth should have decayed into Nickel long ago. Finding it now means it was produced in more recent times, in astronomical terms.
It’s not just the discovery of 53Mn that’s significant; it’s the concentration. Some 53Mn is expected to drift down to Earth as cosmic dust. But it’s unusual to find more of it, like the researchers behind this study did. And its presence means there definitely was a supernova explosion in Earth’s vicinity, about 2.5 million years ago.
“This is investigative ultra-trace analysis,” said Korschinek. “We are talking about merely a few atoms here.” Remarkably, the measurements not only detect the presence of 53Mn, but can also help understand the size of the star it came from. “But accelerator mass spectrometry is so sensitive that it even allows us to calculate from our measurements that the star that exploded must have had around 11 to 25 times the size of the sun,” Korschinek added.
It was too far away to cause a mass extinction, but it likely did shower the Earth with cosmic rays. That likely affected the climate.
“However, this can lead to increased cloud formation,” says co-author Dr. Thomas Faestermann. “Perhaps there is a link to the Pleistocene epoch, the period of the Ice Ages, which began 2.6 million years ago.”
So while it may not have been ultra-calamitous for Earth, it did have an effect.
Some researchers think that the supernova explosion at that time did trigger at least a partial extinction, called the Pliocene marine megafauna extinction. They point to not only the presence of elevated levels of 60Fe, but also to a feature out in space called the Local Bubble. It’s a gigantic, cavernous hole in the interstellar medium caused by one or more supernovae explosions. Now, the discovery of 53Mn just strengthens that hypothesis.