Extinct Species

More than 99% of every species that has ever existed on Earth is already extinct — meaning extinction, not survival, is actually the historical norm.

Cheat Sheet

Extinction, the complete disappearance of a species, is a natural part of life's history — over 99% of all species that have ever existed on Earth are now extinct.
Mass extinction events, periods where a large share of species die out in a relatively short geological time, have occurred at least five times in Earth's history, most famously the event that ended the dinosaurs' reign.
The most widely supported explanation for the dinosaur extinction roughly 66 million years ago is a massive asteroid impact, combined with resulting climate disruption, though other contributing factors are still debated.
Unlike the mass extinctions of the deep past, the current elevated rate of species loss is widely attributed primarily to human activity, including habitat destruction, climate change, and overexploitation.
Scientists distinguish between background extinction, the normal, gradual rate of species loss over time, and mass extinction events, which occur at a dramatically accelerated rate.
Some conservation efforts focus specifically on "de-extinction" research, using genetic techniques to attempt reviving traits or, controversially, entire extinct species, though this remains scientifically and ethically contested.

The 60-Second Version

Extinction, the complete disappearance of a species, is a natural part of life's history — over 99% of all species that have ever existed on Earth are now extinct. Mass extinction events, periods where a large share of species die out in a relatively short geological time, have occurred at least five times in Earth's history, most famously the event that ended the dinosaurs' reign. The most widely supported explanation for the dinosaur extinction roughly 66 million years ago is a massive asteroid impact, combined with resulting climate disruption, though other contributing factors are still debated. Unlike the mass extinctions of the deep past, the current elevated rate of species loss is widely attributed primarily to human activity, including habitat destruction, climate change, and overexploitation. Scientists distinguish between background extinction, the normal, gradual rate of species loss over time, and mass extinction events, which occur at a dramatically accelerated rate. Some conservation efforts focus specifically on "de-extinction" research, using genetic techniques to attempt reviving traits or, controversially, entire extinct species, though this remains scientifically and ethically contested.

The Long Version

Extinction as the Historical Norm

Given the sheer span of Earth's roughly 3.7-billion-year history of life, the overwhelming majority, over 99%, of every species that has ever existed has already gone extinct, a reflection of how normal species turnover actually is across deep evolutionary time, rather than an unusual or rare occurrence.

The Five Mass Extinction Events

Beyond the ordinary, gradual background rate of extinction, Earth's history includes at least five identified mass extinction events, periods of geologically rapid, widespread species loss affecting a large share of life on the planet simultaneously. The most well-known is the event that ended the roughly 165-million-year reign of the dinosaurs, though earlier, even more severe mass extinctions occurred deeper in Earth's history.

What Actually Killed the Dinosaurs

The leading scientific explanation for the mass extinction roughly 66 million years ago centers on a massive asteroid impact, evidenced by a large impact crater and a distinct global sediment layer containing material consistent with an extraterrestrial impact, which likely triggered catastrophic climate disruption, including reduced sunlight and dramatic temperature swings that most large dinosaur species couldn't survive. Some researchers also point to contributing factors like large-scale volcanic activity occurring around the same time.

Today's Elevated Extinction Rate and Its Cause

Unlike the deep-past mass extinctions driven by asteroid impacts or volcanic activity, the current elevated rate of species loss, which many researchers argue may constitute an ongoing sixth mass extinction, is attributed primarily to human activity: habitat destruction, climate change, overexploitation through hunting and fishing, and the introduction of invasive species to new environments.

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Glossary

Mass extinction: A relatively short geological period in which a large share of Earth's species die out.
Background extinction rate: The normal, gradual rate of species loss occurring outside of mass extinction events.
Asteroid impact hypothesis: The leading scientific explanation for the extinction event that killed the dinosaurs roughly 66 million years ago.
De-extinction: Genetic research efforts aimed at reviving traits or species that have gone extinct.
Endangered species: A species currently at significant risk of extinction, distinct from one that has already gone extinct.