I remember a theory of a rouge planet, or possibly gas giant or burned out sun in such a huge orbit that it took a hundred thousand years or so for it to cycle back through the solar system. Other theories show at approximately the same time something so big coming thru that it's mere gravitational interaction blew Mars and Earth into a different orbit, and another puts creation of the Ort Cloud at about that time period with something about comets having such a similar path that they might be from some such origin. Be kind of interesting if it turned out all of them happened due to the same object making a visit here.