List of extinction events and their significance

Identification and criteria

Mass extinctions are recognized in the fossil record by sudden reductions in diversity and abundance, changes in ecosystem structure, and disruption of long-running lineages. Scientists use stratigraphic correlation, shifts in isotopic chemistry, and extinction rate analyses to identify events. Quantifying increases in the extinction rate relative to background levels is central to defining an extinction event.

Major examples (the "Big Five")

• Ordovician–Silurian — an early large loss associated with glaciation, sea-level fall and habitat loss in shallow seas.
• Late Devonian — a prolonged interval of biotic turnover that heavily affected marine reef communities and many fish groups.
• Permian–Triassic — the most severe known extinction, producing extensive losses in marine invertebrates and terrestrial vertebrates and linked to massive volcanism and climate change.
• Triassic–Jurassic — a transition with large losses that helped open ecological space for archosaurs and dinosaurs.
• Cretaceous–Paleogene (K–Pg) — famous for the disappearance of non-avian dinosaurs, associated with an asteroid impact and major environmental change.

Other notable declines

Beyond the classic five, the fossil record shows regionally important crises, diversity troughs and shorter-lived biotic collapses. Some intervals show repeated pulses of extinction rather than a single instantaneous event; these can be driven by prolonged environmental stress such as ocean anoxia, sea-level fluctuation, or rapid climate shifts.

Causes and evidence

Proposed drivers include large bolide impacts, extensive volcanic eruptions (flood basalts), abrupt climate change, sea-level change, ocean oxygen loss and changes to carbon and other biogeochemical cycles. Geologists study rock layers, volcanic ash beds and chemical proxies (geology) to establish timing, while biologists assess the evolutionary consequences (evolution).

Ecological and evolutionary consequences

Mass extinctions reshape ecosystems by removing dominant groups and creating ecological opportunities for survivors. Recovery may take millions of years and often involves adaptive radiations, where surviving lineages diversify to fill vacated niches. These turnovers influence long-term patterns of biodiversity and the distribution of major clades.

Relevance to the present

Studies of past extinction events provide context for contemporary biodiversity loss. Human activities are driving habitat destruction, pollution, invasive species spread and rapid climate change that can accelerate extinction rates. Comparing modern trends with deep-time events helps conservation scientists identify vulnerabilities and targets for mitigation.

Further reading and data

For summaries, stratigraphic charts and datasets that track extinction and speciation through time, consult specialized reference works and databases. Primary resources include compilations of fossil occurrences, isotope records and extinction-rate analyses (extinction rate data). For introductory context on the disciplines involved see resources on geology and evolution, and general treatments of biodiversity and species concepts. Historical overviews and educational materials often situate these events within the wider history of life on Earth.