The Milky Way is not a passive backdrop to life on Earth; its structure and high-energy environment leave measurable imprints in both astrophysical data and the geological record. In this talk, I will outline our current understanding of the Galaxy’s mass distribution, spiral structure, and the role of dark matter in shaping its dynamics. Variations in cosmic-ray flux, driven by the Solar System’s motion through spiral arms and its vertical oscillation about the Galactic plane, are recorded in meteorites and cosmogenic isotopes. The latter variations stem from the controversial (yet very real) influence of cosmic rays on cloud radiative properties, supported by physical mechanisms, laboratory experiments, and atmospheric-chemistry studies. An apparent inconsistency between geological and astronomical measurements turns out to arise from a previously unaccounted dynamical effect. Once included, it leads to surprising implications for the dark-matter content of the Galactic disk. Together, these results indicate that Earth’s climate history provides a unique, independent probe of the Milky Way’s structure and the nature of dark matter.