When people think of extinction, they often picture the asteroid that ended the reign of the dinosaurs 66 million years ago. Yet long before that catastrophe, Earth endured four earlier mass extinction events—each one a planetary crisis that wiped out the majority of life.
These events were not isolated tragedies but turning points in Earth’s history. Each extinction reshaped ecosystems, eliminated dominant species, and opened opportunities for survivors to evolve into new forms of life. Collectively, they remind us of both the fragility and resilience of life on a planetary scale.
What Counts as a Mass Extinction?
Scientists define a mass extinction as a period when Earth loses at least 75% of species in a relatively short geological timeframe. These events differ from background extinctions, the slower and constant disappearance of species over time.
Over the past 500 million years, Earth has experienced five major mass extinctions. Four of them occurred before the age of dinosaurs, making them some of the deadliest and least familiar catastrophes in natural history.
1. The Ordovician-Silurian Extinction (≈443 Million Years Ago)
The first major extinction occurred about 443 million years ago, near the end of the Ordovician period. At that time, Earth’s oceans were filled with diverse marine life, including trilobites, brachiopods, and early coral reefs.
What Caused It?
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A short, intense ice age is believed to have locked up massive amounts of water in glaciers.
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This drop in sea levels destroyed shallow marine habitats where most life thrived.
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As the climate shifted back to warmth, ecosystems were stressed further, compounding losses.
Impact
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Roughly 85% of marine species vanished.
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Entire reef systems collapsed, reshaping early ocean ecosystems.
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Yet some lineages, including early jawed fish, survived and diversified afterward.
2. The Late Devonian Extinction (≈372–359 Million Years Ago)
The Devonian period is often called the “Age of Fishes,” as seas teemed with armored fish, early sharks, and the ancestors of amphibians venturing onto land. But this age ended in a series of drawn-out crises spanning nearly 20 million years.
What Caused It?
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Widespread ocean anoxia (loss of oxygen in seas), possibly triggered by massive plant expansion on land altering carbon cycles.
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Volcanic activity and rapid climate fluctuations.
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Asteroid impacts may have also contributed.
Impact
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About 75% of all species were wiped out.
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Reef-building organisms were devastated, and fish diversity plummeted.
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The event cleared the way for land vertebrates to rise, setting the stage for future terrestrial ecosystems.
3. The Permian-Triassic Extinction (≈252 Million Years Ago)
Known as “The Great Dying,” this was the most catastrophic extinction event in Earth’s history. Occurring 252 million years ago, it nearly ended life itself.
What Caused It?
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Colossal volcanic eruptions in Siberia released massive amounts of carbon dioxide and methane.
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Resulting global warming, ocean acidification, and anoxia created hostile conditions.
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Some evidence points to methane hydrate releases and ecosystem collapse as amplifying factors.
Impact
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Up to 97% of all species perished.
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Terrestrial ecosystems collapsed, with only a handful of species surviving.
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Marine life was nearly obliterated, from trilobites to giant amphibians.
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Only about 3% of species endured, but they became the ancestors of all life forms that followed—including reptiles, mammals, and eventually humans.
4. The Triassic-Jurassic Extinction (≈201 Million Years Ago)
By the late Triassic period, early dinosaurs had appeared, but they were not yet dominant. Other reptilian groups, such as crocodile-like archosaurs and giant amphibians, controlled much of the land. That changed abruptly around 201 million years ago.
What Caused It?
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Widespread volcanic eruptions associated with the breakup of Pangaea released greenhouse gases.
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Resulting climate change destabilized ecosystems and caused ocean acidification.
Impact
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About 80% of species went extinct.
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Many large reptiles disappeared, clearing ecological space.
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Dinosaurs quickly rose to dominance, beginning their 135-million-year reign.
5. The Fifth Extinction: Dinosaurs’ End (66 Million Years Ago)
While technically beyond the “before the dinosaurs” scope, the Cretaceous-Paleogene extinction deserves mention. An asteroid impact near modern-day Mexico unleashed global firestorms and climate collapse. Dinosaurs (except birds) perished, but mammals flourished in the aftermath.
Survivors: The “Living Fossils”
Despite the devastation, certain species endured multiple mass extinctions. Some, like horseshoe crabs, sharks, and coelacanths, remain remarkably unchanged after hundreds of millions of years. Their survival strategies—adaptability, resilience, or ecological flexibility—earned them the nickname “living fossils.”
Lessons From Ancient Catastrophes
Understanding these past extinctions is not only about history—it is about perspective. They remind us that:
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Life is fragile yet resilient. Catastrophes can erase most species, but survivors adapt and thrive.
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Evolution is shaped as much by loss as by innovation. Extinctions open ecological niches for new forms of life.
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Today’s biodiversity is the result of countless near-deaths and recoveries.
Studying these events also provides cautionary insights into modern environmental change. While today’s species face human-driven pressures rather than volcanic super-eruptions, the outcome—a dramatic loss of biodiversity—could echo the past if left unchecked.
Conclusion: Earth’s Deadliest Days, Our Shared Inheritance
Long before the asteroid that ended the age of dinosaurs, Earth endured multiple mass extinctions that reshaped the trajectory of life. From the icy seas of the Ordovician to the fiery devastation of the Permian, each crisis destroyed—but also created.
The ecosystems we know today, from forests to coral reefs to human societies, exist only because a small fraction of life survived these earlier apocalypses. By studying them, we not only uncover the resilience of life but also recognize our responsibility to protect it for the future.
