The Big Five: Earth's Mass Extinction Events

Five times in the last 500 million years, life on Earth has been pushed to the brink. These mass extinctions — defined as events that eliminated more than 75% of species in a geologically short time — dramatically reshaped the biosphere, ending dominant lineages and opening the door for new ones.

1. End-Ordovician Extinction (444 Mya)

Species lost: ~85% of marine species

The earliest of the Big Five struck at the end of the Ordovician Period. A severe glaciation — triggered by the movement of the supercontinent Gondwana over the South Pole — caused sea levels to plummet and ocean temperatures to drop. Marine organisms adapted to warm, shallow seas were devastated.

The extinction unfolded in two pulses: the first caused by glaciation and habitat loss, the second by the rapid warming and ocean anoxia that followed as glaciers melted. Trilobites, brachiopods, and graptolites suffered enormous losses, though all three groups eventually recovered.

2. Late Devonian Extinction (372–359 Mya)

Species lost: ~75% of species

The Late Devonian extinction was not a single event but a series of pulses spanning millions of years, with the Kellwasser event (372 Mya) and Hangenberg event (359 Mya) as the most severe. Reef ecosystems were devastated — coral reefs essentially vanished and did not recover for 100 million years.

The causes remain debated. Possible triggers include massive volcanic eruptions, the spread of land plants (which altered weathering and nutrient cycles), oceanic anoxia, and possible bolide impacts. The Late Devonian extinction particularly affected tropical marine organisms.

3. Permian–Triassic Extinction (252 Mya)

Species lost: ~90% of marine species, ~70% of terrestrial vertebrate species

The "Great Dying" is the worst mass extinction in Earth's history. It came devastatingly close to ending complex life entirely. The primary cause was massive volcanism in the Siberian Traps — an eruption lasting roughly a million years that released enormous quantities of CO₂, methane, and toxic gases.

The cascading effects were catastrophic: extreme global warming, ocean acidification, ocean anoxia, ozone depletion, and toxic metal poisoning. Marine ecosystems collapsed. On land, the diverse synapsid and amphibian faunas of the Permian were nearly wiped out.

Recovery took 10 million years — the longest of any mass extinction. But the empty niches eventually allowed archosaurs (including dinosaurs) to rise to dominance.

4. End-Triassic Extinction (201 Mya)

Species lost: ~76% of all species

At the Triassic–Jurassic boundary, another volcanic catastrophe struck — this time the Central Atlantic Magmatic Province (CAMP), associated with the breakup of Pangaea. The eruptions released vast amounts of CO₂, causing rapid warming, ocean acidification, and widespread anoxia.

Many large amphibians, early archosaur groups, and most non-dinosaurian large reptiles went extinct. Crucially, dinosaurs survived — and with their competitors eliminated, they diversified explosively in the Jurassic, beginning their 135-million-year reign.

5. Cretaceous–Paleogene Extinction (66 Mya)

Species lost: ~75% of species, including all non-avian dinosaurs

The most famous mass extinction ended the Age of Dinosaurs. A ~10 km asteroid struck what is now the Yucatan Peninsula in Mexico, creating the Chicxulub crater. The impact released energy equivalent to billions of nuclear weapons, triggering global wildfires, a "nuclear winter" of dust and soot, acid rain, and a years-long collapse of photosynthesis.

Non-avian dinosaurs, pterosaurs, marine reptiles, and ammonites vanished. But small mammals, birds, crocodilians, and many plant groups survived, setting the stage for the Cenozoic radiation of mammals.

Patterns and Lessons

Several patterns emerge from studying mass extinctions:

• Volcanism and impacts are the primary triggers, but their damage is inflicted through climate change, ocean chemistry disruption, and ecosystem collapse
• Recovery takes millions of years — typically 5–10 million years for ecosystems to return to pre-extinction diversity levels
• Generalists survive — organisms with broad diets, wide geographic ranges, and tolerance for environmental variation tend to fare better
• Extinctions create opportunity — every mass extinction was followed by an adaptive radiation as surviving lineages diversified into empty niches

Are We in a Sixth Extinction?

Many scientists argue that human activities — habitat destruction, pollution, climate change, and overexploitation — are driving a sixth mass extinction. Current species loss rates are estimated at 100–1,000 times the background rate. While the scale does not yet match the Big Five, the trajectory is concerning.

The fossil record teaches us that mass extinctions are survivable — life has always recovered — but that recovery operates on timescales of millions of years.

Explore the timeline of these events with our Geologic Timeline Explorer, or learn about what are fossils and how they document Earth's dramatic history.