A new study suggests that cosmic radiation from a supernova explosion 2.5 million years ago may have accelerated viral evolution in Africa's deepest lake.

Over 400 miles long, Lake Tanganyika, between Burundi, Democratic Republic of Congo, Tanzania and Zambia, is the world's second-largest freshwater lake. Between two and three million years ago, the number of virus species infecting fish in the lake mysteriously mushroomed. That timeframe coincides with the passing of the solar system through the wall of what astronomers called the Local Bubble. Although it's a relatively empty region of space, its exterior is busy with stardust -- the remains of stars.

Stardust comes from supernovae, powerful stellar explosions that release vast amounts of energy and cosmic rays into space. When these cosmic rays reach Earth, they can affect the planet's atmosphere and climate, potentially impacting biodiversity.

A supernova is the self-destruction of massive supergiant stars. The explosion -- which can outshine entire galaxies -- typically sees the star run out of nuclear fuel and suffer a core collapse under its own gravity. The star's outer layers are pushed into deep space, spreading elements around a galaxy and theoretically seeding the formation of new stars.

The new paper, published in Astrophysical Journal Letters, examined iron isotopes (iron-60) to identify a 2.5 million-year-old supernova and connected it to a radiation surge that affected Earth around the same time. Their theory states that the blast was powerful enough to break the DNA of living creatures and possibly cause viruses in Lake Tanganyika to mutate into new species. From simulations of the supernova, the researchers found that Earth suffered from cosmic rays for 100,000 years.

"The iron-60 is a way to trace back when the supernovae were occurring," said Caitlyn Nojiri, co-author of the paper and an undergraduate student at the University of California, Santa Cruz. "From two to three million years ago, we think that a supernova happened nearby."

This is not the first time supernovae have been linked to life on Earth. Research published in 2022 indicates a significant link between supernova explosions and the evolution of complex life on Earth. The study found a correlation between the frequency of supernovae over the last 3.5 billion years and the fraction of organic matter buried in Earth's sediments, suggesting that supernova events may influence Earth's climate and the development of life.

Another study published in 2023 using meteorite evidence suggests that our early solar system survived a nearby supernova explosion as it was forming 4.6 billion years ago. Despite the intense radiation and shockwaves, the early solar system not only survived -- thanks to its "birth cocoon" of a filament of molecular gas -- but may have assimilated elements from the explosion.

During the solar system's first 100,000 years, a supernova may have gone off within the "kill zone" -- a region thought to stretch to about 50 light-years.

Earth's ozone layer would be destroyed if there was a supernova right now any closer than 50 light-years from the solar system, allowing the sun's ultraviolet radiation to quickly extinguish all life. The nearest star to the solar system, which is thought to be on the verge of a supernova, is Betelgeuse in the constellation Orion, which is about 550 light-years distant.