IF A SUPERNOVA went off near Earth, that would be bad. From a distance of less than, say, 25 light-years, the resulting bombardment of fast-moving atomic nuclei, known as cosmic rays, would destroy the layer of atmospheric ozone that stops most of the sun’s harmful ultraviolet light reaching Earth’s surface. In combination, these two kinds of radiation, cosmic and ultraviolet, would then kill many forms of life.
If a supernova went off not quite so close by, though, that might be interesting. It would have effects, but more subtle ones. Indeed, a paper published in the latest edition of the Journal of Geology, by Brian Thomas of Washburn University, in Kansas, and Adrian Melott of the University of Kansas, suggests that a series of such stellar explosions may have nudged humanity’s forebears down from their trees and up onto their hind legs.
The chain of events Dr Thomas and Dr Melott propose starts with the observation that between 14 and 20 supernovas have gone off in Earth’s vicinity over the past 8m years. These explosions, of young, massive stars, are believed to have happened in the Tucana-Horologium stellar group, currently about 130 light-years from Earth.
One reason for believing these supernovas occurred is that the shock waves from them swept away nearby interstellar gas and the...