A few million years ago, fish were swimming quite happily in Lake Tanganyika.

The lake itself – now classed as one of Africa’s Great Lakes, with its 673 km long expanse spanning four countries (Burundi, Tanzania, Zambia and the Democratic Republic of Congo) – housed a thriving ecosystem of aquatic life, and had done so for millions of years.

But then, suddenly, these fish found their lives threatened by a mysterious collection of viruses.

And a recent study from UC Santa Cruz has offered one explanation why.

The paper, which was recently published in The Astrophysical Journal Letters, purports that the sudden abundance of virus species that affected fish in the lake was due to something quite surprising.

The explosion of another star in our galaxy.

How did they come to this conclusion? Well, astronomers from the university were exploring the iron isotopes of a supernova that happened 2.5 million years ago.

The element (iron-60) was identified on the sea floor. This element is particularly interesting since it is radioactive, with it isotopes breaking down and becoming non-radioactive over time.

The iron-60 that they discovered was confirmed as forming over two time frames; some was 2.5 million years old, whilst others were 6.5 million years of age.

And where did it come from? The explanation, demonstrated by a simulated model the researchers created, is a supernova which caused the Earth to be pummelled by cosmic rays for up to 100,000 years, causing the 2.5 year old isotopes. The older iron-60 is a result of the Earth passing through the Local Bubble in space and being covered in stardust.

As lead-author Caitlyn Nojiri explained in a UC Santa Cruz statement, the examination of the iron-60 helped them to iron out a significant astronomical mystery:

“The iron-60 is a way to trace back when the supernovae were occurring,” Nojiri said. From two to three million years ago, we think that a supernova happened nearby.”

Following their discovery, the team hypothesized that the radiation from the supernova sufficiently powerful to affect the DNA of creatures on Earth, as Nojiri explained:

“It’s really cool to find ways in which these super distant things could impact our lives or the planet’s habitability. We saw from other papers that radiation can damage DNA. That could be an accelerant for evolutionary changes or mutations in cells.”

The effect? Nojiri and her fellow researchers explored how this new information could be applied to other scientific mysteries from across the world, resulting in their hypothesis that viruses already present in Lake Tanganyika mutated into a new threat.

Though this hypothesis warrants further research to confirm its validity, it seems quite likely, as Nojiri continued:

“We can’t say that they are connected, but they have a similar timeframe. We thought it was interesting that there was an increased diversification in the viruses.”

If this were true, it would solve a mystery that has had scientists scratching their heads for decades.

If you thought that was interesting, you might like to read about the mysterious “pyramids” discovered in Antarctica. What are they?