do cosmic rays reach earth? where they occur most?

Answer 1

Yes, cosmic radiation from space is constantly bombarding the earth. It consists of both gamma radiation and other subatomic particles. This is one source of background radiation that is present in nature, another being radioactive substances from the earth.

I've heard that it's actually a good thing that cosmic radiation exists, because it increases genetic mutations, and has thus sped up evolution. (I'm not a biologist though)

Answer 2

Not the cosmic ray itself but usually what happens is that the cosmic ray hits a molecule in the atmosphere and causes a shower of secondary and tertiary particles. In fact they are particles and not some kind of ray.

http://en.wikipedia.org/wiki/Cosmic_rays

Answer 3

They do reach the earth, but not as many as thousands of years ago before the Van Allen Radiation belt formed which absorbs many of them. Coming from outer space they may come to any area of the earth. Check Van Allen Belt on Google .