Gamma Rays from UltraCompact Minihaloes: Effects on the Earth's
  Atmosphere and Links to Mass Extinction Events
  Recent studies of the effects on the Earth's atmosphere by astrophysical
sources, such as nearby gamma-ray bursts or supernovae, have shown that these
events could lead to severe changes in atmospheric composition. Depletion of
ozone, the most notable of these changes, is extremely dangerous to living
organisms as any decrease in ozone levels leads to an increase in the
irradiance of harmful solar radiation at the Earth's surface. In this work we
consider dark matter as an astrophysical source of gamma rays, by the
annihilation and decay of WIMPs found within dark compact halo objects known as
UltraCompact Minihaloes (UCMHs). We calculate the fluence of gamma rays
produced in this way and simulate the resulting changes to terrestrial ozone
levels using the Goddard Space Flight Center 2D Atmospheric Model. We also
calculate the rate at which such events would occur, using estimates for the
mass distribution of these haloes within the Milky Way. We find that the ozone
depletion from UCMHs can be significant, and even of similar magnitude to the
levels which have been linked to the cause of the Late-Ordovician mass
extinction event. However, the probability of such encounters over the Earth's
entire history is relatively low. This suggests that, while dark compact
objects like UCMHs could have had an impact on the Earth's biosphere, other
astrophysical phenomena like gamma-ray bursts or supernovae seem a more likely
source of these effects.
