Cretaceous–Paleogene extinction event
extinction event ending the Mesozoic Era
The Cretaceous–Paleogene (K–Pg) extinction event, formerly known as the Cretaceous–Tertiary (K–T) extinction event, was a major mass extinction of three-quarters (75%) of the plant and animal species on Earth which occurred around 66 million years ago. The event caused the extinction of all the non-avian dinosaurs and most other tetrapods weighing more than 25 kg (55 lb), excepting some ectothermic species such as sea turtles and crocodilians. It marked the ends of both the Cretaceous period and the Mesozoic era, and logged the beginning of the current geological era, the Cenozoic era.
In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary or K–T boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal iridium, which is more common in asteroids than in the Earth's crust.
It is generally thought that the K–Pg extinction resulted from the impact of a massive asteroid 10 to 15 km (6 to 9 mi) wide, creating the Chicxulub impact crater and devastating the global environment primarily through a lingering impact winter which halted photosynthesis in plants and plankton. The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180 km (112 mi) Chicxulub crater in the Gulf of Mexico's Yucatán Peninsula in the early 1990s. The timing of the ejecta layer, together with the match between fossil‑record ecological patterns and modeled environmental disruptions (such as darkness and cooling), supports the conclusion that the Chicxulub impact triggered the mass extinction.
A 2016 drilling project into the Chicxulub peak ring confirmed that it contained granite ejected within minutes from deep in the Earth, and that it contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region. The gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain.
Begin with the source’s own compact description: “Cretaceous–Paleogene extinction event” is extinction event ending the Mesozoic Era. The dossier treats that line as a proposition to test through Cretaceous, Paleogene and extinction, not as a finished interpretation.
Why this record matters
The phrase “extinction event ending the Mesozoic Era” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
Contemporary correspondence, administrative files and participant testimony can test how later narratives organized the event or institution. The source revision retrieved here is dated Sep 23, 2026. The linked authority identifier is Q55811. The Library of Congress control number is sh2020004499. 1 of 1 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank. The first chronological checks are 2016.
Later summaries often reconcile disputed chronology or motive more neatly than the contemporary record permits. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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Questions for further research
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This entry incorporates text from “Cretaceous–Paleogene extinction event” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.