The Earth is located inside a 1,000 light-year void called the Local Bubble, which was created by a series of supernovae over the eons. Deposits of iron-60 in deep-sea crust samples tell us that one happened about 5 million years ago, and then another went off 2 million years ago. In a new study, researchers calculate that cosmic radiation levels increased by up to a factor of 30 for about 100,000 years after the explosion, increasing mutation rates in organisms.