Isolated by mountains along the East African Rift is Lake Tanganyika. More than 400 miles long, it is the continent's deepest lake and accounts for 16% of the world's available freshwater. Between 2 and 3 million years ago, the number of virus species infecting fish in that immense lake exploded, and in a new study, UC Santa Cruz researchers propose that this explosion was perhaps triggered by the explosion of a distant star.

The researchers connected this stellar explosion to a surge of radiation that pummeled Earth around the same time, and they assert that the blast was powerful enough to break the DNA of living creatures—possibly driving those viruses in Lake Tanganyika to mutate into new species.

Cosmic correlation to mutations

When Nojiri and colleagues simulated what that supernova was like, they found that it hammered the Earth with cosmic rays for 100,000 years following the blast. The model perfectly explained a previously recorded spike in radiation impacting Earth around that time, which had been puzzling astronomers for years.