This talk places new constraints on ocean temperature change across the Neoproterozoic to Phanerozoic transition, when the fossil record documents some of the most dramatic changes in the history of complex life. Traditional δ18O data blur temperature with changes in seawater composition; clumped isotopes break that ambiguity. Using stratigraphically anchored, fabric-targeted sampling, we reconstruct nearshore seawater temperatures and, where possible, infer ice volume from seawater δ18O.

Results reveal large, directional climate shifts with ecological consequences. In the Tonian and Cryogenian, clumped-isotope data from Oman and elsewhere indicate near-modern tropical temperatures before and after Snowball Earth glaciations, suggesting dynamic hydrologic and climatic transitions. During the Ediacaran, post-glacial warming followed by ≥20 °C cooling likely expanded oxygenated habitats and set the stage for early animal diversification. In the Ordovician, ~15 °C of long-term tropical cooling over ~40 Myr culminated in brief but extensive glaciation, providing the climate context for the Great Ordovician Biodiversification Event.

By pairing clumped-isotope temperatures with age control and complementary proxies, we build a quantitative framework linking climate and habitability, showing how temperature change guided life’s evolutionary trajectory through deep time.