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.