At the close of the Permian, life suffered a blow beyond anything in the following hundreds of millions of years. Estimates indicate that roughly 80–90% of marine species and a large fraction of land vertebrates and insects disappeared. It is the most comprehensive of the five great extinctions and is sometimes called the "Great Dying."

The strongest explanation is the vast, long-lived volcanism in what is now Siberia (the Siberian Traps). The erupting basalt released enormous quantities of greenhouse gases; warming, ocean acidification, and oxygen depletion in the seas drove a self-reinforcing collapse. The exact sequence and the relative contributions are still studied; this was not a single trigger but a cascading system failure.

The abrupt change in the rock record shows that species did not merely decline — the structure of ecosystems collapsed. Recovery of biological diversity took millions of years. That gap also opened a door: in the Permian's aftermath, the lineages that would later lead to dinosaurs and mammals found room to expand.