Abstract

The end of the Triassic period was marked by one of the largest and most enigmatic mass-extinction events in Earth's history¹ and, with few reliable marine geochemical records, terrestrial sediments offer an important means of deciphering environmental changes at this time. Tanner et al.² describe an isotopic study of Mesozoic fossil soils which suggests that the atmospheric concentration of carbon dioxide (pCO₂) across the Triassic–Jurassic boundary was relatively constant (within 250 p.p.m.v.), but this is inconsistent with high-resolution evidence from the stomatal characters of fossil leaves³. Here I show that the temporal resolution of the fossil-soil samples may have been inadequate for detecting a transient rise in pCO₂. I also show that the fossil-soil data are consistent with a large increase in pCO₂ across the Triassic–Jurassic boundary when variations in the stable carbon isotope (denoted as ¹³C) in terrestrial plant leaves are taken into account. These factors suggest that the linkage between pCO₂, global warming and the end-Triassic mass extinction remains intact.