Life on Earth has faced catastrophic collapses five times over the past 500 million years. Each event wiped out a significant percentage of species, resetting the evolutionary trajectory of the planet. Understanding these mass extinction events in Earth history helps scientists assess the current biodiversity crisis. This article examines each of the five major extinctions, their causes, the survivors, and the long recovery periods that followed. While the immediate triggers differ, each event shares a common pattern: rapid environmental change that outpaced the ability of most species to adapt, followed by millions of years of ecological rebuilding.
Mass Extinction Events in Earth History: The Ordovician-Silurian Extinction and Glaciation
The first of the five major extinctions occurred approximately 443 million years ago, at the boundary between the Ordovician and Silurian periods. This event unfolded in two distinct pulses and is the only mass extinction known to have been driven primarily by glaciation.
Causes of mass extinction events in Earth history
The primary driver was a rapid shift from a greenhouse climate to an icehouse climate. The supercontinent Gondwana moved toward the South Pole, triggering extensive glaciation. As ice sheets expanded, sea levels dropped by an estimated 100 to 150 meters. This drained shallow continental seas where most marine life lived, eliminating the habitats that sustained the majority of species at the time.
The second pulse occurred when the glaciers melted rapidly, leading to anoxic conditions in the oceans. Oxygen levels plummeted, suffocating many organisms that had survived the first pulse. This two-phase pattern of cooling followed by warming and anoxia is a recurring theme in mass extinction events in Earth history, though the timescale varies.
mass extinction events in Earth history and what was lost
This extinction eliminated approximately 85 percent of marine species, a figure supported by research published in Science (Sheehan, 2001). The victims included many trilobite families, brachiopods, echinoderms, and graptolites. Reef-building organisms suffered heavily, as the loss of shallow-water habitats disproportionately affected sessile filter feeders. The event hit shallow-water communities harder than deep-water communities, which provided a refuge for some groups.
Recovery and Survival After Mass Extinction Events in Earth History
Survivors included some brachiopods, cephalopods, and primitive fish. Conodonts, early jawless vertebrates, also persisted. Recovery took roughly 5 to 10 million years, during which time ecological communities slowly reassembled. The Silurian period that followed saw the diversification of jawed fishes and the first land plants, setting the stage for terrestrial ecosystems.
Exploring Mass Extinction Events in Earth History: The Late Devonian Extinction
The Late Devonian extinction was not a single event but a series of extinction pulses spread over 20 million years, peaking around 372 million years ago. This prolonged duration distinguishes it from the other major extinctions, which occurred over shorter intervals.
Causes
The most likely cause involves ocean anoxia combined with the spread of land plants. Early vascular plants, such as ferns and lycophytes, expanded rapidly during the Devonian. Their root systems accelerated soil formation and rock weathering. This process drew down atmospheric carbon dioxide, causing global cooling. Nutrient runoff from the new soils also triggered algal blooms that depleted marine oxygen, creating dead zones along continental margins. Unlike the asteroid impact that ended the Cretaceous, this extinction demonstrates how biological innovations can inadvertently destabilize planetary systems.
The Toll of Mass Extinction Events in Earth History
Species extinctions in the marine realm reached roughly 70 to 80 percent. The victims included many coral species, stromatoporoids (ancient reef builders), and almost all jawless fishes. Trilobites lost many families but did not go extinct entirely. The famous Dunkleosteus, a large armored fish, disappeared at the end of this interval. Reef ecosystems collapsed and did not fully recover until the Mesozoic.
What Survived and Recovery
Surviving groups included many lobe-finned fishes, amphibians, and the first reptiles. Recovery was slow because the extinction occurred in pulses over a long time span, preventing a single recovery window. The Carboniferous period that followed saw the rise of vast coal swamps and the diversification of amphibians and insects.
The Permian-Triassic Extinction: The Great Dying
The Permian-Triassic extinction, approximately 252 million years ago, stands as the most severe biodiversity crisis in Earth history. It is often called the Great Dying. No other extinction event approached its magnitude in terms of species loss or ecosystem disruption. This event remains a critical case study among mass extinction events in Earth history.
Causes
The leading hypothesis points to massive volcanic eruptions in the Siberian Traps, a region in present-day Russia. These eruptions lasted for roughly 1 million years and released enormous volumes of carbon dioxide, sulfur dioxide, and methane. The immediate effects included global warming of 5 to 8 degrees Celsius, ocean acidification, and widespread anoxia.
The warming triggered the release of methane clathrates from seafloor sediments, further amplifying the greenhouse effect. Scientists estimate that the event wiped out 90 to 96 percent of marine species and 70 percent of terrestrial vertebrate species, according to research by Benton (University of Bristol) and colleagues (Benton & Newell, 2014, Gondwana Research). The combination of multiple kill mechanisms working in concert made this the deadliest of all mass extinction events in Earth history.
What Was Lost
The Great Dying eliminated most coral species, trilobites entirely, and many brachiopod and mollusk groups. On land, many synapsids (the ancestors of mammals) disappeared. The dominant herbivorous and carnivorous reptiles of the Permian went extinct. In the oceans, reef systems vanished entirely, and it took more than 10 million years for complex reef-building organisms to reappear.
What Survived and Recovery
Survivors included some species of bivalves, gastropods, and the conodonts that had persisted through earlier extinctions. Early ancestors of dinosaurs, such as archosaurs, also survived. Recovery was exceptionally slow. Ecosystems did not stabilize for 5 to 10 million years, and some functional groups took even longer to reestablish. The first dinosaurs appeared in the Triassic period that followed.
The Triassic-Jurassic Extinction: Volcanism and Ocean Acidification
The fourth major extinction occurred approximately 201 million years ago, at the Triassic-Jurassic boundary. This event cleared the way for dinosaur dominance, though the dinosaurs themselves were not the primary beneficiaries of the extinction, they simply outcompeted the surviving groups in the recovery period.
Causes
Massive volcanic activity in the Central Atlantic Magmatic Province (CAMP) is the primary cause. The eruptions coincided with the breakup of the supercontinent Pangaea. They released vast amounts of carbon dioxide, causing global warming of 3 to 4 degrees Celsius. Ocean acidification and anoxia followed. The emissions from CAMP were similar in scale to the Siberian Traps but occurred over a shorter timeframe, which may explain the sharper extinction pulse.
What Was Lost
Species extinction rates in the marine realm reached about 75 percent. Many ammonite groups, conodonts, and coral species disappeared. On land, many large amphibians and early crocodile relatives went extinct. The extinction hit the pseudosuchians (crocodile-line archosaurs) harder than the early dinosaurs, giving the latter a competitive advantage in the recovery period.
What Survived and Recovery
Survivors included the earliest dinosaurs, which had already appeared in the late Triassic. Pterosaurs, marine reptiles, and many lizard ancestors also persisted. Recovery occurred relatively quickly, within 1 to 2 million years, likely because the extinction did not completely dismantle ecological networks. The Jurassic period that followed saw dinosaurs diversify into many ecological niches.
The Cretaceous-Paleogene Extinction: The Asteroid Strike
The most famous of the five mass extinctions, the Cretaceous-Paleogene (K-Pg) extinction, occurred 66 million years ago. It ended the reign of non-avian dinosaurs and is the only extinction event linked definitively to an extraterrestrial impact.
Causes
A 10 to 15 kilometer wide asteroid struck the Yucatán Peninsula in what is now Mexico, creating the Chicxulub crater. The impact released energy equivalent to billions of atomic bombs. It triggered a global firestorm, tsunamis, and a long winter caused by dust and sulfur aerosols blocking sunlight. The immediate darkness shut down photosynthesis worldwide, collapsing food chains from the bottom up.
What Was Lost
An estimated 75 to 80 percent of all species went extinct. Non-avian dinosaurs vanished entirely. Pterosaurs, plesiosaurs, and mosasaurs also disappeared. Many ammonite and nautiloid species went extinct. Forests collapsed globally because sunlight was blocked for months. In the oceans, plankton communities crashed, starving filter feeders and the predators that depended on them.
What Survived and Recovery
Survivors included small mammals, birds (avian dinosaurs), and crocodiles. The ability to burrow, swim, or feed on detritus helped these groups survive the impact winter. Recovery took 3 to 5 million years for marine ecosystems and up to 10 million years for terrestrial ecosystems. The Paleogene period saw the rise of mammals and the diversification of flowering plants.
Comparing Rates: The Sixth Extinction
Scientists have identified a potential sixth mass extinction currently underway. The rate of species loss today is significantly higher than the background extinction rate. Background extinction is the natural rate of species loss between mass extinctions, estimated at 0.1 to 1 species per million species per year.
The current extinction rate is estimated to be 100 to 1,000 times higher than the background rate, according to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) Global Assessment Report on Biodiversity and Ecosystem Services (2019). This crisis is driven by human activities: habitat destruction, overexploitation, pollution, climate change, and invasive species. For deeper context, explore our guide to Evolution.
While the first five mass extinctions had natural causes, the sixth extinction has a single species as its primary driver. Whether the recovery will follow the same patterns as previous mass extinction events in Earth history remains an open question.
1. What is the difference between background extinction and mass extinction?
Background extinction is the regular, ongoing loss of species at a low rate, typically 0.1 to 1 species per million species per year. Mass extinction involves a sharp spike in extinction rates that eliminates a large percentage of species across many taxonomic groups within a short geological time frame.
2. Which mass extinction killed the most species?
The Permian-Triassic extinction, also called the Great Dying, wiped out an estimated 90 to 96 percent of marine species. It is the most severe of the five major extinctions.
3. How long did it take for life to recover after each extinction?
Recovery times varied. The Ordovician-Silurian extinction took about 5 to 10 million years. The Late Devonian and Permian-Triassic extinctions required 5 to 10 million years each. The Triassic-Jurassic recovery was faster, about 1 to 2 million years. The Cretaceous-Paleogene extinction recovery took 3 to 10 million years depending on the ecosystem.
4. Did any species survive all five mass extinctions?
No individual species survived all five events, but some groups, such as bacteria, algae, and certain microscopic organisms, have persisted through multiple extinctions. Among animals, conodonts survived the first four but went extinct at the Triassic-Jurassic boundary.
5. Is the sixth extinction inevitable?
The current rate of species loss indicates a potential sixth mass extinction. Whether it becomes a full mass extinction depends on human actions. Conservation efforts, habitat protection, and reductions in pollution and greenhouse gas emissions can slow the rate of extinction.
Sources & References
- Benton, Michael J. When Life Nearly Died: The Greatest Mass Extinction of All Time. Thames & Hudson, 2003.
- Benton, M.J., and A.J. Newell. "Impacts of global warming on Permo-Triassic terrestrial ecosystems." Gondwana Research 25 (2014): 1308-1337. DOI: 10.1016/j.gr.2012.12.010
- Bond, David P.G., and Stephen E. Grasby. "On the causes of mass extinctions." Palaeogeography, Palaeoclimatology, Palaeoecology 478 (2017): 3-29. DOI: 10.1016/j.palaeo.2016.11.005
- Schulte, Peter, et al. "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary." Science 327, no. 5970 (2010): 1214-1218. DOI: 10.1126/science.1177265
- Sheehan, Peter M. "The Late Ordovician Mass Extinction." Annual Review of Earth and Planetary Sciences 29 (2001): 331-364. DOI: 10.1146/annurev.earth.29.1.331
- Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES). Global Assessment Report on Biodiversity and Ecosystem Services. IPBES, 2019. ipbes.net/global-assessment