Glossary

The Cretaceous–Paleogene (K-Pg) extinction event is a mass extinction that occurred approximately 66 million years ago at the boundary between the Cretaceous and Paleogene periods. It is the most recent of the geological 'Big Five' mass extinctions. The primary cause was the impact of an asteroid roughly 10 km in diameter that struck what is now the Yucatán Peninsula of Mexico, forming the approximately 180–200 km wide Chicxulub crater. The impact ejected vast quantities of dust, soot, and sulfate aerosols into the stratosphere, triggering an 'impact winter' that blocked sunlight, shut down photosynthesis, and collapsed food chains globally. Approximately 75% of all species on Earth perished, including all non-avian dinosaurs, pterosaurs, most marine reptiles, ammonites, and many groups of marine invertebrates. Simultaneously, the extinction created vast empty ecological niches that catalyzed the adaptive radiation of mammals and birds, ultimately establishing the ecological foundations of the Cenozoic Era.

The Permian–Triassic extinction event is the most severe mass extinction in Earth's history, occurring approximately 251.9 million years ago at the boundary between the Permian and Triassic periods. High-precision U-Pb geochronology from the Global Stratotype Section and Point (GSSP) at Meishan, China, constrains the main extinction interval to just 61 ± 48 thousand years, between 251.941 ± 0.037 Ma and 251.880 ± 0.031 Ma. The event eliminated an estimated 57% of biological families, 81% of marine species, and approximately 70% of terrestrial vertebrate species. Several major taxonomic groups were driven to complete extinction, including trilobites, rugose and tabulate corals, fusulinid foraminifers, blastoid echinoderms, and eurypterids. The primary cause is widely attributed to the eruption of the Siberian Traps Large Igneous Province, specifically the initial pulse of widespread sill emplacement into the volatile-rich Tunguska sedimentary basin, which liberated massive volumes of greenhouse gases through contact metamorphism of organic-rich sediments. The resulting cascade of environmental disruptions included rapid global warming of approximately 10°C in sea surface temperatures, widespread ocean anoxia and euxinia, carbon cycle disruption evidenced by a sharp negative δ¹³C excursion, and possible ocean acidification. The extinction marks the boundary between the Paleozoic and Mesozoic eras and fundamentally restructured both marine and terrestrial ecosystems. Ecological recovery was protracted, with marine ecosystems requiring at least 5–10 million years and terrestrial vertebrate community diversity not being fully restored for approximately 30 million years, well into the Late Triassic.