The cichlid fish in Lake Tanganyika never knew what was coming. How could they? A star from dozens of lightyears away was to blame for what would soon happen.
Cosmic rays from a nearby supernova would soon rain down on the unsuspecting cichlids, tearing apart their DNA, causing the fish to mutate and opening the door for myriad viruses to infect their population. Or so we think, anyway.
That's the scenario posited by a team led by former University of California (UC) Santa Cruz undergraduate Caitlyn Nojiri.
During her studies of astrophysics, Nojiri became fascinated with cosmic rays, showers of high-energy particles from deep space, and their effects on Earth.
Nojiri cites a 2003 Belgian election that went haywire due to a cosmic ray as one of her early interests. In that case, a cosmic ray is thought to have caused a slight flip in the electronic voting system, incorrectly adding votes to the tally.
"It's insane that something is from space can have that kind of an impact on our electronics," Nojiri told Space.com. "So we're thinking, okay, how does that have a potential impact on other aspects of our life?"
That question initiated her research with UC Santa Cruz professor Enrico Ramirez-Ruiz and postdoctoral fellow Noémie Globus.
"Our project was to model the propagation of cosmic rays from supernova sources to see their potential impacts on life on Earth," Nojiri explained.
A cosmic fishing trip
One particular supernova caught the attention of Nojiri and colleagues.
A study dating iron-60, an isotope of iron that is a byproduct of supernovas, in the seafloor indicated that a nearby supernova likely bombarded the Earth with cosmic rays some 2.5 million years ago.
Simulating the supernova with computer models, the team suggested that the radiation from this stellar explosion pummeled the our planet for around 100,000 years after the event. That radiation was potentially strong enough to break apart DNA.
"But we're not biologists," laughed Nojiri. Thus, the team dug into biology papers to look for clues. And that's when they came across a 2024 study about the cichlids in Lake Tanganyika.
Not only is Lake Tanganyika Africa's largest and deepest lake, but it's also one of the world's 20 most ancient lakes, having formed between 9 million and 12 million years ago.
Lake Tanganyika is perhaps best known by scientists for its incredible biodiversity. More than 2,000 species live in the lake, including some 250 types of cichlids.
With its ancient age and rich biodiversity, Lake Tanganyika is an evolutionary biologist's dream.
That 2003 study indicates that about 2.5 million years ago, cichlids underwent rapid species diversification, which might have impacted virus evolution in the lake, too. This is interesting as Lake Tanganyika's cichlids are disproportionately affected by viruses compared to other fish.
That 2.5-million-year timeframe coincides with Nojiri's supernova, supporting the theory that its DNA-busting radiation might be responsible for the diversity of cichlids and their associated viruses.
"There could have been other factors, but it's definitely interesting," Nojiri pointed out.
Of course, there needs to be far more research to prove this is a case of causation rather than mere correlation, but that research is plausible.
"You could expect to see diversification potentially in other places as well," Nojiri, now looking to continue her studies of astrophysics at the doctoral level, concluded.
So, who's ready for a cosmic fishing trip?
The team's research was published in The Astrophysical Journal Letters.
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