1e:T406,The evolution of Earth's climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow ∼50 Wm^-2 increase in TSI over the last ∼420 million years (an increase of ∼9 Wm^-2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO₂. This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth's long-term habitability. Humanity's fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO₂ not seen since the early Eocene (50 million years ago). If CO₂ continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.1f:T53b,The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms.20:T1499,

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