Lake Tanganyika, located along the East African Rift, is one of the most fascinating and significant bodies of water on Earth. Spanning over 400 miles, it is the deepest lake on the continent and holds about 16% of the world’s available freshwater. This immense lake, isolated by mountains and surrounded by dense ecosystems, has long intrigued scientists. Between 2 and 3 million years ago, the diversity of viruses infecting the fish in the lake dramatically increased, but the causes of this sudden surge in viral species have remained unclear—until now. A recent study conducted by UC Santa Cruz researchers presents a bold hypothesis: that the virus explosion was potentially triggered by the explosion of a distant star.
The Research and Discovery
The research, published in The Astrophysical Journal Letters, was led by Caitlyn Nojiri, a recent undergraduate, with contributions from Professor Enrico Ramirez-Ruiz and postdoctoral fellow Noémie Globus. Their study involved iron isotopes to pinpoint a supernova explosion that occurred around 2.5 million years ago, coinciding with the sudden appearance of new viral species in Lake Tanganyika. By studying these isotopes, the researchers aimed to trace the origins of the cosmic radiation that may have reached Earth and sparked evolutionary changes.
The team’s primary focus was a form of radioactive iron, known as iron-60, which is produced in the aftermath of stellar explosions. This iron isotope is rare on Earth and typically found in seafloor sediments. The researchers analyzed iron-60 samples, determining that some of the isotopes were about 6.5 million years old, while others were around 2.5 million years old. These findings indicated that Earth was impacted by two distinct events: first, a period when the solar system passed through a region rich in cosmic dust (about 6.5 million years ago), and second, a supernova explosion that released a fresh batch of radioactive iron roughly 2.5 million years ago.
The Cosmic Impact
What makes this discovery particularly intriguing is that the second event, the supernova, occurred around the time when significant biological changes were happening on Earth, specifically in Lake Tanganyika. The researchers hypothesized that the radiation from this supernova, which lasted for 100,000 years, bombarded Earth with cosmic rays. These rays would have been strong enough to disrupt DNA at a cellular level, potentially triggering mutations that could have accelerated the evolution of species, including viruses.
“We saw from other studies that radiation can damage DNA,” Nojiri explained. The intense radiation from the supernova might have provided a catalyst for the viruses in Lake Tanganyika to mutate rapidly, diversifying into many new species. While the researchers cannot definitively claim a direct connection, they found it notable that the virus diversification in the Rift Valley lakes seems to align with the timeframe of the supernova’s radiation surge.
This new correlation opens up a fascinating avenue of research into how cosmic events can have far-reaching effects on life on Earth, not just through astronomical phenomena but also through the evolutionary and biological changes they may provoke.
A Deeper Dive into the Past
To understand how these supernovae events might have affected Earth, the researchers dug into stellar history. Their investigation revealed that the Earth entered a massive, open-space region of the Milky Way known as the Local Bubble, a vast cavity in the interstellar medium that contains relatively few stars. As the solar system passed through the bubble’s stardust-rich exterior about 6.5 million years ago, the planet was seeded with iron-60 from earlier stellar explosions. This earlier influx of iron-60 traces the Earth’s passage through this cosmic region.
Then, around 2.5 million years ago, one of the stars near Earth went supernova, emitting an even greater burst of cosmic rays. The explosion delivered a new influx of radioactive iron to the planet, marking the beginning of a period of intense cosmic bombardment. This radiation, in turn, could have significantly impacted the Earth’s atmosphere, ecosystems, and the species that inhabited it, possibly triggering evolutionary changes at a cellular level.
The models and simulations run by the researchers revealed that these cosmic rays likely hit Earth with enough energy to break DNA strands and cause significant genetic mutations. Given that viruses are highly susceptible to genetic changes, it is possible that this cosmic radiation acted as a driving force behind the mutation and diversification of viruses in Lake Tanganyika.
A Surprising Link: The Explosion of Lifeforms
The study not only reveals the immense power of stellar explosions but also raises questions about the role of cosmic rays in evolutionary processes on Earth. A more subtle yet fascinating implication of this research is how lifeforms and the environment interact with external cosmic influences. It suggests that changes in the cosmos—like supernovae—can affect life on Earth in ways that are both unexpected and profound.
The timing of the supernova’s explosion correlates with a period when the Earth was experiencing significant biological changes, including the emergence of new species. These shifts could have been part of a larger evolutionary puzzle, influenced not only by natural selection and environmental pressures but also by the cosmic events that shaped the planet’s destiny.
In Lake Tanganyika, this might have been the catalyst for the explosive increase in virus diversity that occurred during this period. The mutated viruses that emerged may have had a dramatic impact on the ecosystems in the lake, influencing the survival and adaptation of its fish species, and possibly even contributing to the formation of new viral strains.
Caitlyn Nojiri’s Journey
The research was spearheaded by Caitlyn Nojiri, who, despite not initially intending to pursue a career in astronomy, found herself deeply involved in this groundbreaking project. Nojiri’s academic journey took an unconventional path—she spent a long time at community college, unsure of her future. However, when she joined UC Santa Cruz, her life took a dramatic turn, thanks in part to the guidance of Professor Enrico Ramirez-Ruiz.
Encouraged by Ramirez-Ruiz to apply for UC LEADS, a program aimed at helping underrepresented students excel in science, Nojiri found herself immersed in research. Through the program, Nojiri gained the skills and confidence needed to contribute to cutting-edge projects, including this one, which ultimately resulted in her becoming the first UC Santa Cruz undergraduate to be invited to present her work at the prestigious CCAPP Seminar at Ohio State University.
“I was just trying to learn, and now I’m contributing to important discoveries in astrophysics,” Nojiri said, reflecting on her journey. She also took part in Lamat, a research program for students from nontraditional backgrounds. According to Ramirez-Ruiz, it is vital to have diverse voices in science, as people from different walks of life bring unique perspectives to solving complex problems. This, he believes, is exemplified by Nojiri’s work and her ability to approach problems in novel ways.
The Power of Cosmic Events on Earth
The study conducted by UC Santa Cruz highlights the fascinating ways in which distant stars and supernovae can impact life on Earth in ways that extend beyond the immediate cosmos. The connection between cosmic radiation and evolutionary change on Earth is just beginning to be understood, with much more research likely to follow in the future.
This study also underscores the intricate connections between astronomy, evolution, and biology. It serves as a reminder that the universe is far from being a collection of isolated events; rather, it is a dynamic and interconnected system where cosmic phenomena may have profound effects on the planet’s habitability and the evolutionary paths of lifeforms.
In the grand scheme of the cosmos, Earth is just a tiny dot in an unfathomably vast universe. Yet, through the efforts of researchers like Nojiri and her colleagues, we are starting to unravel how these distant cosmic events have shaped and will continue to shape the very nature of life on Earth. Supernovae, it seems, are not just explosions of stars; they are agents of change, perhaps even directing the course of life in ways we are only just beginning to understand.
Reference: Caitlyn Nojiri et al, 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 (2025). DOI: 10.3847/2041-8213/ada27a