My research focuses on young galaxies that formed in the first 2-3 billion years of cosmic time, with a particular emphasis on their chemical abundance patterns. These patterns allow us to determine how quickly galaxies evolved but are notoriously difficult to measure accurately. I recently developed a novel technique to compute gas temperatures, densities, and compositions from spectroscopic observations of individual galaxies, enabling the first detailed chemical studies of young galaxy populations. I also lead a key James Webb Space Telescope program that is delivering the most accurate measurements of early galaxy chemistry to date. As a Packard Fellow, I will develop innovative methods to characterize galaxies’ massive stars, which regulate the evolution of galaxies and the Universe as a whole; my objective is to create the first models of massive stars grounded in our knowledge of young galaxies. Such models are urgently needed to advance our understanding of the early Universe.