History of life on Earth: Mass extinctions

Mass extinction

An event in which a large number of different species become extinct over a relatively short geological period.

Number of major mass extinctions

Five major mass extinctions have occurred throughout Earth's history.

Ordovician mass extinction

Occurred approximately 444 million years ago and was caused by climate changes. Many trilobites became extinct.

Devonian mass extinction

Occurred approximately 383–359 million years ago and was associated with ice ages, global cooling and glaciation. Almost all life forms died out.

Permian mass extinction

Occurred approximately 252 million years ago. It was the most severe mass extinction and was caused by volcanic eruptions.

Triassic mass extinction

Occurred approximately 201 million years ago and was caused by acid rain and a decrease in oxygen in water, destroying many marine life forms.

Cretaceous mass extinction

Occurred approximately 66 million years ago and resulted in the extinction of dinosaurs. It was caused by an asteroid impact that blocked sunlight.

Most severe mass extinction

The Permian mass extinction, approximately 252 million years ago.

Mass extinction of dinosaurs

The Cretaceous mass extinction, approximately 66 million years ago.

Sixth mass extinction

The current biodiversity crisis, which is caused largely by human activities.

Human activities contributing to the sixth mass extinction

Illegal veld fires, illegal hunting and habitat destruction.

Environmental disaster theory

The theory that mass extinctions are caused by environmental disasters such as meteor impacts, severe volcanic activity, radiation from exploding stars or killer diseases.

Failure to adapt theory

The theory that organisms become extinct because they fail to adapt to environmental or habitat changes such as temperature changes, sea-level changes and continental drift.