Scientists are claiming to have found a potential cause of the cyclical mass extinctions Earth has experienced throughout its history. By examining the "roller-coaster" like way the sun orbits the center of our galaxy, scientists discovered that the times when our solar system is at its highest or lowest in relation to the galactic plane corresponded exactly with periods of mass extinction on Earth. It's thought that during those times the entire solar system is more vulnerable to exotic, and dangerous, cosmic rays emanating from intergalactic space. More research must be done, of course, but to my knowledge it's definitely a plausible explanation of these mysterious events.