Abstract: Giant planets are found far more often around metal-rich stars than metal-poor ones, yet most of the Milky Way's stars formed when the typical metallicity was well below solar. Whether those stars could build planets is a question about most of the planets ever formed, and the disks that would answer it are long gone. In this talk, I’ll present how I used thermochemical models to reconstruct what those disks looked like. The chemistry at low metallicity does not simply scale down with the iron content: the balance of oxygen and carbon in the old Galaxy's stars sets how much water ice a disk can make, and the carbon enhancement common among metal-poor stars can leave a disk surprisingly dry, even when it is oxygen-rich relative to iron. I'll then turn to TOI-7019 b, a transiting brown dwarf I discovered orbiting an ancient metal-poor star, and show how these models turn its host's composition into a testable prediction for what JWST should see in its atmosphere. Together, the models and the discovery point to the chemistry of the old Galaxy, and not just its iron content, as what decided where giant planets could form. Hosted by Professor Elisabeth Newton Zoom Link: https://dartmouth.zoom.us/j/93069806358?