Mass Extinction And The Structure Of The Milky Way
  We use the most up to date Milky Way model and solar orbit data in order to
test the hypothesis that the Sun's galactic spiral arm crossings cause mass
extinction events on Earth. To do this, we created a new model of the Milky
Way's spiral arms by combining a large quantity of data from several surveys.
We then combined this model with a recently derived solution for the solar
orbit to determine the timing of the Sun's historical passages through the
Galaxy's spiral arms. Our new model was designed with a symmetrical appearance,
with the major alteration being the addition of a spur at the far side of the
Galaxy. A correlation was found between the times at which the Sun crosses the
spiral arms and six known mass extinction events. Furthermore, we identify five
additional historical mass extinction events that might be explained by the
motion of the Sun around our Galaxy. These five additional significant drops in
marine genera that we find include significant reductions in diversity at 415,
322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent
~60% of its time passing through our Galaxy's various spiral arms. Also, we
briefly discuss and combine previous work on the Galactic Habitable Zone with
the new Milky Way model.
