Extinction

Definition

Extinction is the termination of a kind of organism or of a group of kinds, usually a species. There have been at least five mass extinctions in the history of life on earth, and four in the last 350 million years in which many species have disappeared in a relatively short period of geological time.

History

Five Waves of Annihilation

Over the past 500 million years, life has been nearly erased five times. Each event reshaped the biosphere, opening niches for the survivors and setting the stage for entirely new forms of life to emerge.

The patterns differ — ice ages, volcanic catastrophes, asteroid impacts — but the outcome is always the same: most life dies, and what remains inherits a transformed world.

The Five Mass Extinctions

~445 million years ago

Ordovician–Silurian

One of the most severe extinctions in Earth's history, triggered by glaciation and sea-level drop as Gondwana drifted toward the South Pole.

~85% of species lost

~375 million years ago

Late Devonian

A prolonged series of pulses over millions of years, devastating marine life — particularly reef systems — driven by global cooling and anoxic oceans.

~75% of species lost

~252 million years ago

Permian–Triassic

The "Great Dying." The largest extinction event in Earth's history, linked to massive volcanic eruptions in Siberia and catastrophic greenhouse warming.

~96% of marine species lost

~201 million years ago

Triassic–Jurassic

Volcanic activity associated with the opening of the Atlantic Ocean released enormous CO₂, clearing the path for dinosaurs to dominate.

~80% of species lost

~66 million years ago

Cretaceous–Paleogene

A 10-km asteroid struck the Yucatán Peninsula, triggering wildfires, an impact winter, and the total collapse of food chains — ending the dinosaurs.

~76% of species lost

Now

The Sixth Extinction

The extinction risk of global warming is the risk of species becoming extinct due to climate change. This may be Earth's sixth major extinction — the Anthropocene extinction.

Unlike previous events, the current wave has a single author: human activity. Habitat destruction, pollution, invasive species, and accelerating climate change are compressing into decades what once took millions of years.

Historical Baseline

Background Rate

~0.1 species / million species-years

20th Century Average

Modern Rate

100× above baseline

Current Projection

Anthropocene Rate

Up to 1,000× above baseline

Cascades

Chains of Extinction

The extinction of one species' wild population can have knock-on effects, causing further extinctions. These cascades are especially common with the loss of keystone species: organisms whose role in their ecosystem is disproportionately large relative to their abundance.

Remove a keystone predator and prey populations explode, stripping vegetation, displacing other species. Lose a primary pollinator and the plants that depend on it cannot reproduce. Each loss rewrites the rules for every species that remains.