“The Jan/Feb 98 Issue of Planetary Report has an article by Michael Rampino “The Shiva Hypothesis”. This describes a 30 million year cycle of mass extinctions over the past 540 million years (see diagram). One hypothesis is that this corresponds the the solar system oscillating through the galactic plane as it orbits the Milky Way. Rampino notes that the last crossing of the galactic plane occurred a few million years ago and it has been suggested that this led to a disturbance of comets in the Oort Cloud, some of which could now be approaching the inner solar system.”
Our next trip through the Galactic plane: 2012AD
Fascinating. Maybe the Mayans are right?
That was Eugene Shoemaker’s view also, I think (qualifier due to screwing that up before).