PermianTriassic

The Permian-Triassic, often abbreviated as PermianTriassic, refers to the boundary between the Permian and Triassic periods and the mass extinction event that marks this boundary. It is one of the most significant events in Earth history, transforming life on land and in the oceans.

Dating and magnitude: The boundary occurred about 251.9 million years ago. The associated extinction event, commonly known as the Great Dying, was the most extensive loss of life in Earth's history. Estimates suggest up to 96% of marine species and 70% of terrestrial vertebrate species became extinct. The recovery of biodiversity spanned millions of years and led to major reorganizations of ecosystems.

Causes and evidence: The extinction is generally considered to have resulted from multiple interacting stressors. A leading hypothesis points to massive volcanism in the Siberian Traps, releasing large volumes of greenhouse gases and aerosols that drove rapid warming, ocean acidification, and widespread anoxia. Other contributing factors may have included climate change, disruption of ocean circulation, methane release from destabilized clathrates, sea-level fluctuations, and ecological cascades. The geological record shows accompanying signals such as negative carbon isotope excursions and various geochemical anomalies, though no single cause is universally accepted.

Stratigraphy and boundaries: The Permian-Triassic boundary is globally recognized in the rock record. The Global Boundary Stratotype Section and Point (GSSP) for this boundary is established at the Meishan section in Sichuan Province, China, marking the base of the Triassic.

Impact and recovery: The extinction reshaped ecosystems, eliminating many dominant groups and opening ecological niches. Recovery proceeded gradually during the Early to Middle Triassic, with rapid diversification of some lineages and the later rise of archosaurs and the first true dinosaurs in the late Triassic.