Mass extinction events are dramatic, widespread losses of species that have occurred multiple times throughout Earth's history, fundamentally reshaping the course of evolution.
- Occur when a significant proportion of Earth's species go extinct in a geologically short period.
- Have happened at least five major times in the last 540 million years, known as the "Big Five."
- Each event drastically altered ecosystems, enabling new groups to rise and diversify.
A mass extinction event is when a large proportion of species die out in a relatively short geological time.
The Big Five Mass Extinctions
The "Big Five" mass extinctions are the most significant biodiversity crises in Earth's history, each marking the end of major eras and dramatically reshaping life.
| Name | When (Ma) | % Species Lost | Main Groups Affected |
|---|---|---|---|
| Ordovician-Silurian | ~443 | ~85% | Marine invertebrates |
| Late Devonian | ~372-359 | ~75% | Marine life, reef builders |
| Permian-Triassic (P-T) | ~252 | ~96% | Marine and terrestrial species |
| Triassic-Jurassic | ~201 | ~80% | Marine reptiles, ammonites |
| Cretaceous-Paleogene (K-Pg) | ~66 | ~76% | Dinosaurs, ammonites, many others |
- Ordovician-Silurian: Ice age triggers; mainly marine species lost.
- Late Devonian: Possibly driven by plants altering soils; marine ecosystems hit hard.
- Permian-Triassic: "Great Dying"; volcanic eruptions and greenhouse gases; almost all marine species and many terrestrial species vanished.
- Triassic-Jurassic: Volcanism and climate change; paved way for dinosaur dominance.
- Cretaceous-Paleogene: Asteroid impact and volcanism; ended non-avian dinosaurs and many others.
The Permian-Triassic extinction is known as the 'Great Dying.'
Causes of Mass Extinctions
Multiple factors, often acting together, can drive mass extinctions by disrupting climate, habitats, and ecosystems on a global scale.
| Cause | Description | Example |
|---|---|---|
| Asteroid Impact | Sudden, catastrophic environmental change | K-Pg extinction (66 Ma) |
| Volcanism | Prolonged eruptions release greenhouse gases | P-T extinction (Siberian Traps) |
| Climate Change | Rapid shifts in global temperatures | Various |
| Sea Level Changes | Alteration of marine habitats | Ordovician-Silurian |
| Anoxia | Oxygen depletion in oceans | Late Devonian |
| Biological Factors | Emergence of new species affecting ecosystems | Late Devonian (land plants) |
- Asteroid Impact: Causes “nuclear winter,” blocking sunlight and halting photosynthesis.
- Volcanism: Emits CO2 and SO2, causing warming, acid rain, and ocean acidification.
- Climate Change: Rapid warming or cooling stresses species’ ability to adapt.
- Sea Level Changes: Flood or expose continental shelves, disrupting marine life.
- Anoxia: Oxygen-poor “dead zones” suffocate marine organisms.
- Biological Factors: New organisms may outcompete or disrupt existing ecosystems.
The Cretaceous-Paleogene extinction was caused by an asteroid impact and volcanism.
Impact on Dinosaurs
Mass extinction events directly influenced dinosaur evolution by ending competitors and paving the way for their rise and fall.
- After the Permian-Triassic extinction, early archosaurs (distant dinosaur relatives) diversified.
- The Triassic-Jurassic extinction removed many reptile rivals, enabling true dinosaurs to dominate.
- The Cretaceous-Paleogene extinction ended the reign of non-avian dinosaurs, allowing mammals to rise.
The Triassic-Jurassic extinction paved the way for dinosaur dominance.
Conclusion
Mass extinctions are pivotal episodes in Earth's history, driving profound changes in biodiversity and enabling new life forms to flourish.
- Major die-offs reshape ecosystems and evolutionary trajectories.
- Understanding past extinctions helps us learn about resilience and vulnerability in life.
- Dinosaurs were both beneficiaries and victims of mass extinctions.
Mass extinctions cause a drastic loss of species and major changes in ecosystems.
Asteroid impacts, volcanism, and climate change are known causes of mass extinctions.
The Permian-Triassic extinction is called the 'Great Dying.'
The Cretaceous-Paleogene extinction led to the extinction of non-avian dinosaurs.