Life › Life & humans today
Extinction & mass extinctions
1796 (Cuvier); 'Big Five' named 1982· Theory or idea· Earth, climate & extinctions
Well establishedStrong fossil, genetic or geological evidence.
The idea that species can die out forever, proven in 1796, and that rare catastrophes have wiped out most species at once.
See it on the Life map →What happened
Until the late 1700s, many naturalists believed no species could vanish; Thomas Jefferson hoped explorers might find living mastodons out West. In 1796 Georges Cuvier showed that mammoth and mastodon bones belonged to lost species, making extinction a fact. Later fossil counts revealed a steady 'background' loss plus rare catastrophes. In 1982 David Raup and Jack Sepkoski identified the 'Big Five' mass extinctions, each killing roughly three-quarters or more of species in a geological instant.
Why it matters
It showed life has a history of losses as well as gains: more than 99% of all species that ever lived are extinct, and extinctions repeatedly cleared the way for new groups.
The evidence (fossils, genes, rocks)
Cuvier's comparisons of fossil and living elephants (1796); Raup and Sepkoski's 1982 tally of marine fossil families through time; later databases with over a million fossil records.
Still debated
Whether the Big Five share a common cause (most involve rapid carbon release and warming, one an asteroid), and whether the Late Devonian was a true mass extinction.
Inside this (3)
Connections (8)
▸Late Ordovician mass extinction is one of the Big Five in Extinction & mass extinctionsWell established
The connection
About 445–443 million years ago, a short, sharp ice age chilled seas and drained shallow shelves, then warming followed. In two pulses about 85% of marine species died, including many trilobites, brachiopods and graptolites. Raup and Sepkoski counted it as the first of the Big Five, and it is usually ranked second-largest.
When and how
Recorded in fossil beds worldwide; included in David Raup and Jack Sepkoski's 1982 analysis of marine fossil families at the University of Chicago.
The evidence
Glacial deposits in North Africa, then near the South Pole, oxygen-isotope cooling signals and a sharp drop in fossil diversity at sections such as Dob's Linn, Scotland.
Debates and open questions
What triggered the glaciation: falling carbon dioxide from early land plants and rock weathering, volcanic eruptions, or toxic metals; a nearby gamma-ray burst has little evidence.
▸Late Devonian extinction is one of the Big Five in Extinction & mass extinctionsWell established
The connection
The Late Devonian saw two main crises, about 372 and 359 million years ago, that devastated reefs, armored fish and many marine groups; roughly 70–80% of species vanished overall, estimates vary. It made the Big Five list in 1982, though the drop may reflect fewer new species appearing as much as more dying.
When and how
The Kellwasser (372 million years ago) and Hangenberg (359 million) events, named after German rock layers; counted in Raup and Sepkoski's 1982 tally.
The evidence
Black, oxygen-poor shale layers, carbon-isotope shifts and fossil counts show the losses; dating ties them to the end of two Devonian stages.
Debates and open questions
Causes are unclear: oxygen loss as land plants flushed nutrients into seas, volcanic eruptions, cooling, or several combined. Whether it was a true mass extinction is also argued.
▸The Great Dying (end-Permian extinction) is one of the Big Five in Extinction & mass extinctionsWell established
The connection
The end-Permian extinction 252 million years ago is the largest in the record, killing roughly 80–90% of marine species. It anchors the very concept of mass extinction: an event so large that whole ways of life, such as trilobites and Paleozoic reefs, simply ended. Raup and Sepkoski ranked it first of the Big Five by size.
When and how
Defined at Meishan, China, the reference section for the Permian–Triassic boundary; quantified in 1982 by Raup and Sepkoski and in later fossil databases.
The evidence
Precise uranium-lead dates on volcanic ash at Meishan show the main die-off took perhaps 60,000 years or less; fossil counts across hundreds of sections confirm its scale.
Debates and open questions
Whether land and sea extinctions happened at the same moment, and which killer, heat, acid or oxygen loss, did most of the damage.
▸End-Triassic extinction is one of the Big Five in Extinction & mass extinctionsWell established
The connection
About 201 million years ago, eruptions as the supercontinent Pangaea began to split released carbon and wiped out roughly three-quarters of species, including many crocodile-line reptiles and large amphibians. Dinosaurs survived and soon dominated. It is the fourth of the Big Five and shows how extinctions open opportunities for survivors.
When and how
Central Atlantic Magmatic Province lavas, now found in Morocco, eastern North America and Brazil; boundary section at Kuhjoch, Austria; counted in the 1982 Big Five.
The evidence
Uranium-lead dates show the eruptions and extinction coincide within tens of thousands of years; fossil pollen, footprints and marine fossils record the losses.
Debates and open questions
Some researchers argue its losses were more drawn out than a single mass event; how much it truly cleared the way for dinosaurs is also debated.
▸K–Pg extinction: end of the non-bird dinosaurs is one of the Big Five in Extinction & mass extinctionsWell established
The connection
The K–Pg event is the most recent of the 'Big Five' mass extinctions that David Raup and Jack Sepkoski picked out in 1982 from counts of marine fossil families. It is also the only one with a confirmed asteroid cause, which made it the model case when scientists began asking what triggers mass extinctions.
When and how
University of Chicago, 1982; K–Pg ranks alongside the end-Ordovician, late Devonian, end-Permian and end-Triassic events.
The evidence
Databases of fossil marine families and genera show five sharp spikes in extinction rates above background; K–Pg is one of the clearest, though smaller than the end-Permian.
Debates and open questions
Whether the Big Five share common causes, and whether today's species losses amount to a sixth mass extinction, are actively debated.
▸A sixth mass extinction? would add a sixth to Extinction & mass extinctionsDebated
The connection
Each of the Big Five removed roughly three-quarters or more of species within a geologically short time. Some biologists argue that current loss rates, if continued, would reach that level within a few centuries. That would make the present the sixth mass extinction, and the first caused by a single species.
When and how
Term popularized by Richard Leakey and Roger Lewin's The Sixth Extinction (1995) and Elizabeth Kolbert's 2014 Pulitzer-winning book; quantified by Anthony Barnosky's team in Nature, 2011.
How sure are we?
Comparisons of modern extinction rates with fossil background rates; Barnosky's 2011 study estimated Big Five-level loss could come in about 240–540 years if threatened species are lost.
Debates and open questions
Comparing modern and fossil rates is tricky, since fossils miss many species and short time spans; some scientists argue the 'mass extinction' label is premature.
▸Georges Cuvier proved the reality of Extinction & mass extinctionsWell established
The connection
In 1796 Cuvier compared elephant skulls and jaws and showed that Indian and African elephants were separate species, and that mammoths and the American mastodon differed from both. Animals so large could hardly be hiding unseen, so they must be extinct. Extinction became accepted fact, and Cuvier went on to argue that repeated catastrophes had ended whole faunas.
When and how
Paris, 1796, in a lecture at the new National Institute; expanded in his Researches on Fossil Bones (1812) and Paris Basin work with Alexandre Brongniart.
The evidence
Cuvier's anatomy holds up: modern fossil studies and ancient DNA confirm mammoths and mastodons as distinct, extinct relatives of living elephants.
Debates and open questions
His sudden catastrophes were later set aside for gradual change, then partly revived when asteroid impacts and mass extinctions were recognized from 1980.
▸Mary Anning supplied evidence for Extinction & mass extinctionsWell established
The connection
Anning's ichthyosaurs, plesiosaurs and pterosaur were unlike anything alive. Cuvier had argued extinction from mammoths; her finds showed whole vanished groups of reptiles, supporting the view that Earth had passed through earlier worlds with different life. Henry De la Beche's 1830 painting Duria Antiquior, the first scene of prehistoric life, was based on her finds.
When and how
Lyme Regis, England, 1811–1840s; her specimens were studied in London by the Geological Society and discussed in Paris by Cuvier.
The evidence
Her surviving specimens and the papers describing them; De la Beche sold prints of Duria Antiquior to raise money for her.
Debates and open questions
How much credit she received in her lifetime versus later; her own recorded words suggest she felt others profited from her work.