Hot acidic Late Permian seas stifle life in record time

The end of Permian time (252–251 Ma) hosts the largest mass extinction in Earth history, yet events heralding this global catastrophe remain intensely disputed. We present a chemostratigraphic marker, the 187Re/188Os ratio, which soars to unprecedented levels approaching the Permo-Triassic boundary. These ratios are tied to profound trace element changes and a precise Re–Os time record at 252 Ma preserved in black shales from East Greenland and the mid-Norwegian shelf. Within a 36-meter shale section, an 80-fold increase in Re concentrations (two-fold for Os) signals seawater conditions that became increasingly inhospitable to life. Unwavering initial 187Os/188Os ratios of 0.6 preclude mafic volcanism and meteorite impact as the direct cause of Late Permian anoxia. We argue that extraordinarily high 187Re/188Os ratios are the hallmark of simultaneously rising ocean temperature and acidity, leading to loss of oxygen and the stifling of life in latest Permian time.