The Core Idea
Five Resets in the History of Life
The 'Big Five' mass extinctions are the five most severe extinction events identified in the fossil record, each eliminating a substantial fraction of all species alive at the time — ranging from roughly 75% to as much as 96% of species, depending on the event. These aren't simply larger versions of the ordinary background extinction rate that happens constantly; they represent sudden, catastrophic disruptions, typically driven by a specific identifiable cause like massive volcanism, glaciation, or an asteroid impact.
Studying these five events matters far beyond simple historical interest — many scientists argue that a sixth mass extinction, driven by human activity, is underway right now, with current extinction rates estimated at 100 to 1,000 times the normal background rate, making the Big Five directly relevant to understanding today's biodiversity crisis.
💡 Memory Trick
The Big Five, in chronological order: End-Ordovician, Late Devonian, End-Permian, End-Triassic, K-Pg — remember it as 'Old Dogs প Try Killing' (or more simply, just picture five dominoes falling one after another across geologic time, each one bigger than the last except the third, which stands out as the single biggest domino of all five — the End-Permian, aka 'the Great Dying,' the worst extinction in Earth's history). Anchoring the End-Permian firmly in the middle as 'the worst one' is the single most important fact to lock in about this whole topic.
The Five Events
Cause and Severity of Each
1
End-Ordovician (444 Ma)
Roughly 85% of species lost, driven by rapid glaciation and associated sea level drop.
Example: this extinction marks the boundary between the first and second Paleozoic periods.
2
Late Devonian (375–360 Ma)
Roughly 75% of species lost, associated with widespread ocean anoxia (oxygen-depleted seawater).
Example: this event unfolded more gradually than the other four, occurring over an extended window rather than a single sharp event.
3
End-Permian ('The Great Dying', 252 Ma)
The single worst extinction in Earth's history — roughly 96% of marine species and 70% of terrestrial species lost. Caused by massive Siberian Traps volcanism, triggering volcanic winter and ocean acidification.
Example: the End-Permian extinction is so severe that some researchers describe it as the closest life on Earth has ever come to being completely wiped out.
4
End-Triassic (201 Ma)
Roughly 80% of species lost, driven by massive volcanism associated with the Central Atlantic Magmatic Province.
Example: this extinction cleared ecological competition, helping enable the subsequent rise of dinosaurs to dominance in the Jurassic.
5
K-Pg (66 Ma)
Roughly 76% of species lost, caused by the Chicxulub asteroid impact combined with ongoing Deccan Traps volcanism. Best known as the extinction that eliminated the non-avian dinosaurs.
Example: the K-Pg extinction is the most famous of the Big Five largely because it ended the age of dinosaurs and opened the door for mammalian dominance.
A Possible Sixth
The Modern Extinction Debate
Many researchers argue Earth may currently be experiencing a sixth mass extinction, this time driven by human activity (habitat destruction, climate change, pollution, and overexploitation) rather than volcanism or asteroid impact. Current species extinction rates are estimated at 100 to 1,000 times the normal background rate — a pace that, if sustained, could eventually rival the severity of the historical Big Five.
🖥️ Applied Scenario
A student is given the estimated cause and severity of an unlabeled extinction event and must identify which of the Big Five it describes.
1
The event shows roughly 96% marine species loss and evidence of massive volcanic activity in what is now Siberia. This is identified as the End-Permian extinction — the worst of the Big Five.
2
A second event shows roughly 76% species loss and a thin layer of iridium-enriched sediment at the boundary, along with evidence of Deccan Traps volcanism. This is identified as the K-Pg extinction, caused by the Chicxulub asteroid impact.
3
The student notes that while both events involved volcanism to some degree, only the K-Pg extinction shows direct asteroid impact evidence (the iridium layer), distinguishing it clearly from the purely volcanism-driven End-Permian event.
📌 Exam Application
Exams commonly give you a percentage species loss and/or a specific cause (volcanism, glaciation, asteroid, ocean anoxia) and ask you to identify which of the Big Five it describes — memorize both the approximate severity and the specific cause of each event, since these details are what actually distinguish them from each other.
⚠️ Most Common Mass Extinctions Mistakes
Don't assume every mass extinction was caused by an asteroid — only the K-Pg extinction has strong direct asteroid impact evidence; the other four were driven primarily by volcanism, glaciation, or ocean chemistry changes. Also don't underestimate the End-Permian extinction's severity relative to K-Pg — despite K-Pg being far more famous (thanks to the dinosaurs), the End-Permian was actually considerably more severe.
✓ Quick Self-Test
1) List the Big Five mass extinctions in chronological order. 2) Which extinction was the most severe, and what caused it? 3) What evidence specifically points to an asteroid impact for the K-Pg extinction?
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