Global temperature records span less than two centuries, but proxies like tree rings and isotope ratios help reconstruct past climates. However, going back beyond a million years is challenging due to fewer preserved proxies. Notable exceptions include the Paleocene-Eocene Thermal Maximum (PETM). Recently, researchers combined proxy records and climate models to reconstruct Earth’s climate over the last half-billion years, revealing a strong link between carbon dioxide and global temperatures. This study focused on oxygen isotope ratios in sea organism shells, despite uncertainties about the constancy of these isotopes in oceans over time.