Lake Tanganyika, located along the East African Rift, is over 400 miles long, the deepest lake in Africa, and holds 16% of the world’s freshwater. Around two to three million years ago, the number of viruses infecting fish in the lake increased dramatically.
Researchers at UC Santa Cruz suggest the explosion of a distant star might have caused this.
A recent study by Caitlyn Nojiri and professors Enrico Ramirez-Ruiz and Noémie Globus analyzed iron isotopes to identify a 2.5 million-year-old supernova. The researchers linked this explosion to a radiation surge that hit Earth simultaneously. They believe the radiation was strong enough to break the DNA of living organisms, possibly causing the viruses in Lake Tanganyika to mutate into new species.
The researchers started by examining iron-60, a radioactive form of iron from exploding stars found on the seafloor. They determined its age by measuring how much it had turned into nonradioactive forms. They found two different ages: some iron-60 formed 2.5 million years ago, and other atoms formed 6.5 million years ago.
The first-ever discovery of an extraterrestrial radioactive isotope on Earth
To find the origin of the iron, they traced the movements of celestial bodies. Our solar system is in an ample open space called the Local Bubble. Earth entered this bubble and passed through its stardust-rich edge about 6.5 million years ago, which brought the older iron-60. Then, a nearby star exploded between 2 and 3 million years ago, adding the newer radioactive iron to our planet.
Nojiri said, “The iron-60 is a way to trace back when the supernovae occurred. We think a supernova happened nearby from two to three million years ago.”
When the team simulated the supernova, they discovered it bombarded Earth with cosmic rays for 100,000 years after the explosion. Their model provided a clear explanation for a previously unexplained spike in radiation on Earth around that time, which had been a mystery to astronomers for years.
The simulation of the supernova suggested that its cosmic rays hit Earth with enough force to break DNA strands. As radiation can damage DNA, this could accelerate evolutionary changes or cause cell mutations.
At the same time, the researchers found a study on virus diversity in one of Africa’s Rift Valley lakes. They noticed that the timing of the increased virus diversity matched the timeframe of the supernova. Although they can’t say if the events are connected, they found the coincidence intriguing.
Caitlyn Nojiri’s journey to becoming a published astronomer began at community college. She later transferred to UC Santa Cruz, where she received support from programs like UC LEADS and Lamat, which help underrepresented students in science. Nojiri is now applying for a Ph.D. in astrophysics.
Journal Reference:
- Caitlyn Nojiri, Noémie Globus, and Enrico Ramirez-Ruiz. Life in the Bubble: How a Nearby Supernova Left Ephemeral Footprints on the Cosmic-Ray Spectrum and Indelible Imprints on Life. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/ada27a
