Stability of atmospheric CO2 levels across the Triassic/Jurassic boundary

The Triassic/Jurassic boundary, 208 million years ago, is associated with w idespread extinctions in both the marine and terrestrial biota. The cause o f these extinctions has been widely attributed to the eruption of flood bas alts of the Central Atlantic Magmatic Province(1-4). This volcanic event is thought to have released significant amounts of CO2 into the atmosphere, w hich could have led to catastrophic greenhouse warming(5-7), but the eviden ce for CO2-induced extinction remains equivocal. Here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations, spann ing a 20-Myr period across the Triassic/Jurassic boundary. Using a standard diffusion model(8,9), we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000-4,000 p.p.m. increase(4,5). The relative stability of atmospheric CO2 across this boundary suggests th at environmental degradation and extinctions during the Early Jurassic were not caused by volcanic outgassing of CO2. Other volcanic effects-such as t he release of atmospheric aerosols or tectonically driven sea-level change- may have been responsible for this event.