Investigations into the impact of astronomical phenomena on the
  terrestrial biosphere and climate
  This thesis assesses the influence of astronomical phenomena on the Earth's
biosphere and climate. I examine in particular the relevance of both the path
of the Sun through the Galaxy and the evolution of the Earth's orbital
parameters in modulating non-terrestrial mechanisms. I build models to predict
the extinction rate of species, the temporal variation of the impact cratering
rate and ice sheet deglaciations, and then compare these models with other
models within a Bayesian framework. I find that the temporal distribution of
mass extinction events over the past 550 Myr can be explained just as well by a
uniform random distribution as by other models, such as variations in the
stellar density local to the Sun arising from the Sun's orbit. Given the
uncertainties in the Galaxy model and the Sun's current phase space
coordinates, as well as the errors in the geological data, it is not possible
to draw a clear connection between terrestrial extinction and the solar motion.
In a separate study, I find that the solar motion, which modulates the Galactic
tidal forces imposed on Oort cloud comets, does not significantly influence
this cratering rate. My dynamical models, together with the solar apex motion,
can explain the anisotropic perihelia of long period comets without needing to
invoke the existence of a Jupiter-mass solar companion. Finally, I find that
variations in the Earth's obliquity play a dominant role in triggering
terrestrial deglaciations over the past 2 Myr. The precession of the equinoxes,
in contrast, only becomes important in pacing large deglaciations after the
transition from the 100-kyr dominant periodicity in the ice coverage to a
41-kyr dominant periodicity, which occurred 0.7 Myr ago.
