On the link between cosmic rays and terrestrial climate

We discuss the problem of cosmic ray diffusion in the Milky Way and show that the spiral arm dynamics gives rise to a ∼ 150 Myr periodic modulation of the cosmic ray density in the vicinity of the solar system. We show that these predicted variations are recorded in the exposure ages of Iron meteorites. Given the suspected cosmic ray-climate link, we argue that spiral arm passages are also responsible for the periodic appearance of ice age epochs on Earth. This hypothesis is supported by the clear correlation between ice age epochs and the meteoritic record and also between longer term activity in the Milky Way and glacial activity on Earth.