The forces leading to the origin and persistence of complex life on Earth are a fundamental question in modern science. Why did complex life emerge on our planet, and how did it spread across Earth’s surface? How did animals’ first habitats shape their biology, behavior, and future? I work to answer these questions by integrating sedimentology and geochronological data from multiple radioisotopic systems. In this talk, I will share new age constraints on Earth’s largest negative carbon isotope excursion and discuss how they illuminate the potential drivers of this geochemical event and its effects on early animals. I will also present insights into how sedimentation rates, a key control on Earth’s biogeochemical systems, changed during the rise of early animals. These results derive, in part, from new geochronological constraints I have worked to establish in Oman. Finally, I describe a hypothesis connecting expanding shallow marine environments with early animal diversification, highlight the major challenges to this hypothesis, and identify the still-outstanding data needed to test it.