In 1983, a scientist named Richard Muller came up with an interesting theory to explain the almost regular interavals between mass extinctions on Earth.
Roughly every 26 million years, the Earth suffers a massive extinction event in which whole species and ecosystems disappear. It's widely believed and accepted by the scientific community that the extinction events are precipitated by the impacts of comets and asteroid impacts, but what Muller devised to explain the almost regular event was rather scandalous - what if the sun had an evil twin brother?
Muller theorized that, orbiting the sun at a great distance, is another star - possibly a red or brown dwarf which orbits the sun once every 26 million years at a distance of 1 to 3 light years (this is very distant when you consider that the closest known star, Proxima Centauri, is only 4.2 light years away!) When the star, which Muller named Nemesis after the Greek goddess of divine retribution, gets close to the sun thanks to an irregular orbit, it disturbs the Oort Cloud, the grouping of icy comets and bodies at the edge of our solar system, and sends them on a collision course towards the inner planets.
For more info http://slightlywarped.com/crapfactory/a ... iltwin.htm
Don't try to troll me 'coz you're going straight to my ignore list.