Mass Extinctions in Earth History
Compare the five major mass extinction events in Earth history (End-Ordovician, Late Devonian, End-Permian, End-Triassic, K-Pg), describe proposed kill mechanisms for each (glaciation, oceanic anoxia, volcanic mega-eruptions, asteroid impact), and explain why mass extinctions, while catastrophic, also open ecological space for subsequent evolutionary radiations
What a learner can do afterwards
- Names all five major mass extinctions in chronological order with approximate dates
- Describes the End-Permian extinction as the most severe and links it to the Siberian Traps volcanic eruption and its atmospheric consequences
- Explains how each mass extinction was followed by an adaptive radiation, e.g. the K-Pg extinction removing non-avian dinosaurs allowed mammals to diversify and eventually produce humans
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The K-Pg asteroid impact ended the non-avian dinosaurs about 66 million years ago. It was the latest of the five major mass extinctions called the Big Five. The earliest was the End-Ordovician, about 444 million years ago. Between them came the Late Devonian, End-Permian, and End-Triassic events. Late Devonian extinctions severely affected marine life, including reefs; widespread low-oxygen seas were one important pressure. These events had different causes, though some effects were similar.
The End-Permian extinction, about 252 million years ago, is generally considered the most severe of the Big Five. Siberian volcanic eruptions released gases that warmed Earth and disrupted the oceans, including oxygen loss. Estimates of species losses vary. Stanley's 2016 study estimated about 81% of marine species were lost. Older estimates often gave 90 to 96%. This chart shows the 2016 estimate, not a count of all species on Earth.
Mass extinctions destroy species, but surviving lineages can later diversify into available ecological roles. This is adaptive radiation. It depends on suitable resources and opportunities, not empty space alone. After K-Pg, mammals diversified as ecosystems recovered. In an island example, surviving birds with enough food might spread into different habitats; isolated populations could later evolve into new forms. Recovery and diversification can take millions of years.
The Big Five had different causes. The End-Permian was the most severe; estimates of its losses vary. Survivors can diversify as ecosystems recover.
More to read
27.4 The Evolutionary History of the Animal Kingdom
The Big Five are five major extinction intervals, not occasions when all animal life disappeared. The End-Permian crisis about 252 million years ago is generally considered the most severe and is linked to Siberian volcanism and environmental disruption. Loss estimates vary: Stanley (2016) estimated about 81% of marine species, below older estimates of 90 to 96%. After the K-Pg crisis 66 million years ago, surviving mammal lineages diversified as ecosystems recovered.
Are we in a modern mass extinction?
Researchers compare present extinction rates with background rates and with past crises. Estimates depend on which species are counted, the time interval, and gaps in the records. Human activity contributes to many current threats, including habitat loss and overexploitation. Studying these pressures helps identify actions that could reduce further losses.
Dino Doom
An asteroid struck near present-day Mexico about 66 million years ago. Dust and other material reduced sunlight, disrupting plants and food webs. Non-avian dinosaurs died out, while some bird lineages survived. Flight alone does not explain survival: many flying animals also disappeared. The crater, iridium-rich boundary layer, and fossil changes provide evidence linking the impact with the extinction.
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