Some 300,000 tons of the element iridium was laid down in the Earth's crust at this time, and high levels of iridium have also been found in asteroids. Suggested explanations have included high volcanic activity blocking sunlight and poisoning the atmosphere, and supernova explosions. But there's no geological evidence for coincident volcanic activity, and supernova explosions don't occur close enough at a sufficiently high rate. Dar was the first to suggest that collapsing neutron stars might be to blame. He and his colleagues have studied the likely effects of the cosmic ray jets flung out by neutron star collapses, and their conclusions, to be published next week in the journal Physical Review Letters, make chilling reading.
Cosmic rays are a very serious threat.
Entering the Earth's atmosphere, the jets create showers of lethal high-energy subatomic particles known as muons. As they rain down on the Earth, the muons have enough energy to irradiate and kill almost every living thing in their way. Such an intense dose would destroy the central nervous system, causing death within a couple of days. The cosmic ray burst can last up to a month, during which time muons would also destroy the ozone layer, irradiate the environment and damage vegetation, severing the food chain. Thanks to the Earth's rotation, and radiation borne on atmospheric winds, the effect would be quickly spread around the globe.