"Actually, this isn't correct. The KT event happened 65 million years ago and the earth goes around the Milky Way once every 230 million years.
But that's irrelevant. That spot in the Milky Way didn't stand still, it orbits with us so it's not like we would be coming back into the same hazards again. The hazards orbit with us. They can't remain stationary.
Furthermore, those hazards are much more local. They are the asteroids which are part of our solar system. It is very unlikely that the earth would ever be hit by an orphan asteroid (inter-stellar, i.e. not already orbiting Sol
#39 | Posted by goatman at 2013-10-07 08:55 AM |"
It's true the Milky Way has a rotational period of ~230 My and any hazards in the Solar System's 'neighborhood' would also move along with it. However, there's some evidence indicating that the Solar System goes around the Milky Way along a path that peridically takes it above-through-below the plane of the Milky Way. As such, the Solar System's neighborhood would then experience a varying density/gravity environment such that the frequency of asteroid bombardments could periodically vary. See below:
"Since the mid-1980s, a number of authors have claimed to have identified periodic variations in the impact rate. Using crater data, notably the age estimates for the different craters, they derive a regular pattern where, every so-and-so-many million years (values vary between 13 and 50 million years), an era with fewer impacts is followed by an era with increased impact activity, and so on.
One proposed mechanism for these variations is the periodic motion of our Solar System relative to the main plane of the Milky Way Galaxy. This could lead to differences in the way that the minute gravitational influence of nearby stars tugs on the objects in the Oort cloud, a giant repository of comets that forms a shell around the outer Solar System, nearly a light-year away from the Sun, leading to episodes in which more comets than usual leave the Oort cloud to make their way into the inner Solar System and, potentially, towards a collision with the Earth."