The birth of the idea of extinction
Into the 18th century many people held that species made by God could not vanish. In 1796 the French anatomist Georges Cuvier showed that mammoth bones belonged to a species different from living elephants, the first proof that extinction is real. Cuvier believed Earth had suffered repeated sudden "revolutions", whereas Charles Lyell and Charles Darwin, in the 1859 Origin of Species, treated extinction as a gradual process over long spans of time. In 1982 David Raup and Jack Sepkoski at the University of Chicago statistically analysed the fossil record of thousands of marine families and picked out five extinctions far above the background rate — the "Big Five".
| Extinction | When (million years ago) | Species lost (est.) | Leading explanation |
|---|---|---|---|
| End-Ordovician | ~445 | ~85% | Glaciation and sea-level fall |
| Late Devonian | ~372 | ~75% | Ocean anoxia and other factors |
| End-Permian | ~252 | 90%+ | Siberian Traps eruptions, warming, acidification |
| End-Triassic | ~201 | ~75–80% | Central Atlantic volcanism |
| End-Cretaceous | ~66 | ~75% | Asteroid impact (Chicxulub) |
The asteroid that ended the dinosaurs
In 1980 the physicist Luis Alvarez, his geologist son Walter and colleagues found that 66-million-year-old clay at Gubbio, Italy, held dozens of times the normal amount of iridium, rare in Earth's crust, and argued that an asteroid about 10 km wide had wiped out the dinosaurs. The idea met fierce resistance until the roughly 180-km Chicxulub crater on Mexico's Yucatán Peninsula was identified in 1991. The impact unleashed enormous tsunamis, wildfires, and dust and sulfate aerosols that blotted out the sun and halted photosynthesis. Whether the huge Deccan Traps eruptions in India also contributed is still being studied. Birds are the surviving descendants of dinosaurs.
The Great Dying and the sixth extinction
At the end of the Permian, about 252 million years ago, more than 90% of marine species disappeared. In 2014 Seth Burgess and colleagues used high-precision dating to show the extinction unfolded within about 60,000 years, overlapping with vast Siberian volcanic eruptions; floods of carbon dioxide appear to have driven rapid warming, ocean acidification and oxygen loss. After each mass extinction, natural selection and adaptive radiation filled empty niches, opening the ages of dinosaurs and later mammals. In 2011 Anthony Barnosky and colleagues, and in 2015 Gerardo Ceballos and colleagues, warned that habitat destruction, overexploitation and climate change are now removing vertebrates tens to hundreds of times faster than the background rate, so a sixth mass extinction may be under way. Elizabeth Kolbert's The Sixth Extinction won the 2015 Pulitzer Prize. Because nowhere near 75% of species have yet been lost, researchers stress that action now can still prevent it.
FAQ
- Did all the dinosaurs die out at once?
- Non-bird dinosaurs vanished in a geologically very short time after the impact 66 million years ago. Birds, a branch of the dinosaurs, survived and number more than 10,000 species today.
- Are we really in a sixth mass extinction?
- Extinction rates are approaching mass-extinction levels, but the share of species lost is still far below the Big Five. Scientists therefore describe it as under way or beginning — and preventable with conservation.
Sources reviewed: 2026-10-26
References
- Cuvier, G. (1812). Recherches sur les ossemens fossiles de quadrupèdes. Paris: Deterville.
- Darwin, C. (1859). On the Origin of Species by Means of Natural Selection. London: John Murray.
- Alvarez, L. W., Alvarez, W., Asaro, F., & Michel, H. V. (1980). Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science, 208(4448), 1095–1108.
- Raup, D. M., & Sepkoski, J. J. (1982). Mass extinctions in the marine fossil record. Science, 215(4539), 1501–1503.
- Hildebrand, A. R., et al. (1991). Chicxulub crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatán Peninsula, Mexico. Geology, 19(9), 867–871.
- Erwin, D. H. (2006). Extinction: How Life on Earth Nearly Ended 250 Million Years Ago. Princeton: Princeton University Press.
- Burgess, S. D., Bowring, S., & Shen, S. (2014). High-precision timeline for Earth's most severe extinction. PNAS, 111(9), 3316–3321.
- Barnosky, A. D., et al. (2011). Has the Earth's sixth mass extinction already arrived? Nature, 471(7336), 51–57.
- Ceballos, G., et al. (2015). Accelerated modern human-induced species losses: Entering the sixth mass extinction. Science Advances, 1(5), e1400253.
- Kolbert, E. (2014). The Sixth Extinction: An Unnatural History. New York: Henry Holt.