A shower of matter from space millions of years ago could have led to drastic changes in the Earth's climate, followed by the extinction of life on a massive scale, which also killed off the dinosaurs... Incidentally, cosmic weather might also be a decisive factor in the speed of evolution. The cosmic rays from which we are protected by the solar wind are so full of energy that they can change the DNA of living beings.

This article looks at how "clouds of interstellar matter" can interfere with the solar wind, and allow more cosmic rays to hit earth, therefore causing more mutations!