Earth's history is defined by five catastrophic, and sometimes mysterious, mass extinctions

Science · Published 7 October 2026 Swipe more like this →

In short: While we understand the asteroid that ended the dinosaurs, many of Earth's greatest biological collapses remain unsolved. From the 'Great Dying' to the vanishing of the megalodon, these events reshaped life on a geological timescale, often driven by shifts in carbon cycles and climate.

A mass extinction is defined by the loss of approximately 75% of species within a short geological window—typically less than 2.8 million years. While the Cretaceous-Paleogene extinction 66 million years ago is widely attributed to an asteroid, it is actually an exception. Most mass extinctions are driven by major disruptions to the carbon cycle, such as massive volcanic eruptions that release heat-trapping gases, leading to global warming, ocean acidification, and anoxia.

The Ordovician-Silurian extinction, occurring roughly 443 to 444 million years ago, wiped out about 85% of species. Scientists suggest this was triggered by plummeting temperatures and massive glaciation, potentially caused by the weathering of the Appalachian Mountains, which sucked carbon dioxide from the atmosphere and caused sea levels to drop. Conversely, the Devonian extinction 374 million years ago killed about three-quarters of species, primarily marine invertebrates, though the exact trigger remains unknown.

The most devastating event was the Permian-Triassic extinction, or the 'Great Dying,' 250 million years ago. Beyond these global catastrophes, smaller-scale mysteries persist. The megalodon, a shark reaching over 60 feet and 100 tons, vanished between 28 and 1.5 million years ago, possibly due to oceanic cooling or the loss of its whale prey. Similarly, the Rocky Mountain locust disappeared less than 30 years after its devastating 1873–1877 swarms, potentially due to changes in buffalo habitats or agricultural irrigation.

Today, researchers are investigating whether human activity is triggering a sixth mass extinction, as species are currently vanishing at an unprecedented rate compared to the natural background extinction rate.

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