The Triassic-Jurassic extinction, roughly 201.6 million years ago, wiped out a substantial fraction of life on Earth and ranks among the five worst mass extinctions in the fossil record. Its cause was not an asteroid but a colossal volcanic event that split the supercontinent Pangaea apart, flooding the atmosphere with gases that destabilized both climate and ocean chemistry. The event is less famous than the dinosaur-killing extinction 66 million years ago, but it reshaped terrestrial ecosystems just as profoundly, clearing the ecological stage for dinosaurs to dominate for the next 135 million years.
When It Happened and How We Know
Pinning down the timing of a mass extinction that occurred more than 200 million years ago requires extremely precise radiometric dating. Uranium-lead dating of zircon crystals in volcanic ash layers sandwiched between the last Triassic fossils and the first Jurassic ones places the boundary at about 201.6 million years ago. One key study dated ash beds sitting between the final occurrences of late Triassic ammonite genera and the earliest Jurassic replacements, arriving at an age of 201.58 million years with an uncertainty of less than 200,000 years in either direction.1Earth and Planetary Science Letters. Precise U–Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery That level of precision matters, because it allows researchers to test whether the extinction happened at the same time as a candidate cause or millions of years earlier, which is exactly the kind of test that rules suspects in or out.
The Volcanic Culprit
The leading cause of the extinction is volcanism on a scale that dwarfs anything in human experience. As Pangaea began rifting apart, a vast igneous province called the Central Atlantic Magmatic Province (CAMP) erupted across what would eventually become parts of eastern North America, northwestern Africa, southwestern Europe, and northeastern South America. The lava flows and intrusions cover millions of square kilometers and represent one of the largest volcanic events in Earth’s history.
Geochronology links the start of CAMP eruptions directly to the extinction horizon. Zircon dating shows the earliest volcanism and the mass extinction are synchronous, and that magma release continued in four distinct pulses spread across roughly 600,000 years, meaning the eruptions were still going even as ecosystems began trying to recover.2PubMed. Zircon U-Pb geochronology links the end-Triassic extinction with the Central Atlantic Magmatic Province Independent geochemical confirmation comes from mercury spikes in sediments around the world. Volcanic eruptions inject large amounts of mercury into the atmosphere, and researchers have found clear increases in mercury concentrations right at the extinction boundary in globally distributed rock sections, confirming a volcanically driven disruption of the global mercury cycle at precisely the right time.3PubMed Central. Mercury evidence for pulsed volcanism during the end-Triassic mass extinction
How Volcanism Kills on a Global Scale
A single volcanic eruption, even a large one, does not cause a mass extinction. CAMP was different because of its duration, its immense volume, and the cocktail of gases it released. The kill mechanisms operated on different timescales and hit different parts of the biosphere in different ways.
Volcanic Winters on Land
The initial, most dramatic effect was cooling, not warming. Massive eruptions inject sulfur dioxide into the stratosphere, where it forms sulfate aerosols that reflect sunlight and drop temperatures sharply. These “volcanic winters” were transient but intense, lasting years to decades per eruptive pulse. Recent work correlating sub-centennial-scale lava pulses with the extinction record points to these short-lived volcanic winters as a plausible key agent of extinction for tropical land animals.4PubMed Central. Correlation of sub-centennial-scale pulses of initial Central Atlantic Magmatic Province lavas and the end-Triassic extinctions Lowered temperatures and reduced light levels hit large-bodied, uninsulated reptiles hardest, decimating medium- to large-sized non-dinosaurian reptile groups on land.5PubMed Central. Arctic ice and the ecological rise of the dinosaurs For animals that could not regulate their body temperature internally or lacked insulation, a sudden cold snap lasting several years could be lethal across an entire population.
CO₂ Warming and Ocean Acidification
While sulfate aerosols washed out of the atmosphere within a few years, the CO₂ released by the eruptions accumulated over centuries and millennia, eventually flipping the climate from cold snaps into prolonged greenhouse warming. The oceans absorbed much of that CO₂, which lowered seawater pH and made it harder for organisms to build calcium carbonate shells and skeletons. Calcium isotope records from marine sediments in the eastern Tethys Ocean show a sharp shift right at the extinction boundary, interpreted as a collapse in carbonate burial driven by CO₂-induced ocean acidification. The isotope and carbon cycle data together provide strong evidence linking volcanic CO₂ emissions, ocean acidification, and the marine extinction.6Gondwana Research. Tethyan ocean acidification triggered the end-Triassic mass extinction: New Ca isotopic constraints from the Qiangtang Basin
So the killing worked in two stages: sulfate aerosols caused rapid cooling that hammered land animals first, while accumulating CO₂ drove longer-term warming and acidification that gutted marine ecosystems over thousands of years.7PubMed Central. Correlation of sub-centennial-scale pulses of initial Central Atlantic Magmatic Province lavas and the end-Triassic extinctions
Ocean Oxygen Loss
Warming oceans hold less dissolved oxygen, and nutrient runoff from a disrupted carbon cycle can fuel algal blooms that consume what remains. Evidence from the Tethys Ocean suggests that oxygen-depleted conditions extended up into the sunlit surface waters near the extinction boundary, a state called photic-zone anoxia. Geochemical indicators including the size distributions of tiny pyrite crystals and concentrations of metals sensitive to oxygen levels point to an abrupt onset of this deep oxygen depletion right at the extinction horizon.8Journal of the Geological Society. Biological extinction and photic-zone anoxia across the Triassic–Jurassic transition: insights from the Qiangtang Basin, eastern Tethys For marine animals, acidified water that also lacked oxygen was a double blow, leaving almost nowhere to survive.
Methane as an Amplifier
Some researchers have proposed that the initial warming from volcanic CO₂ triggered the release of methane stored in frozen deposits on the seafloor, creating a feedback loop that amplified the greenhouse effect far beyond what volcanism alone could produce. Modeling of the carbon isotope record suggests this scenario best fits the geochemical data. One estimate puts the total carbon released at roughly 8,000 to 9,000 gigatons from volcanic CO₂ plus an additional 5,000 gigatons from destabilized methane hydrates.9Global Biogeochemical Cycles. Biogeochemical constraints on the Triassic‐Jurassic boundary carbon cycle event For context, total human CO₂ emissions since industrialization amount to roughly 700 gigatons of carbon. The end-Triassic carbon injection was an order of magnitude larger, spread over thousands of years rather than centuries, but still fast enough to overwhelm Earth’s ability to buffer the change.
Why Not an Asteroid?
The extinction that ended the age of dinosaurs 66 million years ago was caused by an asteroid impact, so a natural question is whether the Triassic-Jurassic extinction was too. There is a candidate: the Manicouagan crater in Quebec, one of the largest visible impact structures on Earth, roughly 100 kilometers across. For a time, it was considered a possible trigger. But uranium-lead dating of zircons from the impact melt rock shows the Manicouagan impact occurred at about 214 million years ago, a full 12 million years before the end-Triassic extinction at about 202 million years ago.10Geology. Did the Manicouagan impact trigger end-of-Triassic mass extinction? That timing gap is too large for any plausible delayed-effect mechanism. More recent work confirms this, establishing the impact as middle to late Norian in age, well before the end of the Triassic.11Geosciences. Evidence of Ejecta from the Late-Triassic Manicouagan Impact in the Blomidon Formation, Fundy Basin, Canada
No other impact structure of sufficient size has been linked to the correct time window. Unlike the Cretaceous-Paleogene extinction, there is no iridium anomaly or shocked quartz at the Triassic-Jurassic boundary pointing to a bolide. The case for volcanism, by contrast, has only gotten stronger with every new dating study and geochemical proxy. The asteroid hypothesis for this particular extinction is effectively dead.
What Died
The Triassic-Jurassic extinction hit both land and sea, though the casualties differed between the two realms. In the oceans, reef-building organisms were devastated. Coralline sponges and many groups of bivalves disappeared or were severely reduced. Ammonites, the shelled cephalopods that serve as index fossils for this period, suffered heavy losses at the boundary. Conodonts, eel-shaped jawless vertebrates whose tiny tooth-like elements are ubiquitous in Triassic marine sediments, went extinct entirely.
On land, the hardest-hit group was the pseudosuchians, the broader lineage that includes crocodilians and their many extinct relatives. During the Triassic, pseudosuchians were the dominant large land animals. They filled ecological roles later occupied by dinosaurs: apex predators, large herbivores, and armored grazers. The extinction wiped out almost all of this diversity. Crocodylomorpha, the lineage that includes modern crocodilians and their closest extinct relatives, was the only pseudosuchian group that survived into the Jurassic.12PubMed Central. Triassic-Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs Many other reptile groups, including several lineages of large-bodied herbivores and carnivores that had been diverse throughout the late Triassic, vanished. Among amphibians, the large temnospondyls that had persisted since the Paleozoic were mostly eliminated.
How Dinosaurs Came Out on Top
Dinosaurs existed before the extinction. They had been present since the middle to late Triassic, roughly 230 million years ago, but they were generally small-bodied and ecologically subordinate to pseudosuchians and other reptile groups. The extinction changed that equation by removing the incumbents.
How much of the dinosaurs’ subsequent dominance was due to this ecological release and how much was baked into their own biology is debated. One analysis of body-size evolution across dinosaur lineages found that the burst of body-size diversification in dinosaurs was concentrated in the Triassic itself, before the extinction removed competitors, suggesting that key innovations in Triassic dinosaurs may have mattered more than the disappearance of rivals.13PLOS Biology. Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage In other words, dinosaurs may not have simply filled empty niches after the extinction; they may have already been evolving the traits that would make them successful, and the extinction merely removed the last barriers.
One proposed advantage is insulation. Research on sauropodomorphs, the lineage that eventually produced the giant long-necked dinosaurs, found direct statistical evidence that these animals were adapted to cooler climatic conditions compared to pseudosuchians. This tolerance for cold may have been enabled by an insulating body covering inherited from the common ancestor of dinosaurs and pterosaurs.14Current Biology. Climatic constraints on the biogeographic history of sauropodomorph dinosaurs during the Triassic-Jurassic transition If volcanic winters drove the initial killing on land, animals with insulation and possibly higher metabolic rates would have had a critical survival edge. The very mechanism that destroyed pseudosuchians may have preferentially spared dinosaurs.
How Fast Did Life Bounce Back?
Recovery timescales varied by group. In the oceans, ammonites recovered remarkably quickly. The genus Psiloceras, the first post-extinction ammonite lineage, appeared and diversified globally in what may have been less than 100,000 years after the crisis. These animals spread from Pacific deep waters to the shallow seas of northwestern Europe and even rare occurrences in the Tethys, rapidly differentiating into several major lineages that would seed all subsequent Jurassic and Cretaceous ammonite diversity.15Palaeogeography, Palaeoclimatology, Palaeoecology. Geochronological constraints on post-extinction recovery of the ammonoids and carbon cycle perturbations during the Early Jurassic That said, the total duration of the first post-extinction stage, the Hettangian, was no more than about 2 million years, which compressed the entire early recovery into a geologically brief window.16Earth and Planetary Science Letters. Precise U–Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery
Reef ecosystems took much longer. Coral reefs, which had been built largely by different organisms in the Triassic than in later periods, did not fully recover for millions of years into the Jurassic. This lag is common after mass extinctions: complex, multi-species structures like reefs require a stable environment and a diverse cast of interacting species, both of which take time to re-establish after a catastrophe.
On land, crocodylomorphs provide an interesting case study. Having barely survived the extinction as the sole pseudosuchian lineage, they underwent a rapid radiation in the early Jurassic, diversifying into a range of body sizes and ecological roles.17PubMed Central. Triassic-Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs Early Jurassic crocodylomorphs included small terrestrial runners, marine forms, and larger predators. The diversity they achieved in the aftermath of the extinction, ironically enabled by the loss of their own close relatives, underlines how mass extinctions create evolutionary opportunity even as they destroy established lineages.
Biogeographic Patterns Across Pangaea
The extinction did not play out identically everywhere. Because Pangaea was still a single supercontinent, land animals could theoretically disperse widely, but regional differences in climate, geography, and ecosystem structure meant the extinction and recovery had distinct regional flavors. Analysis of how similar animal communities were across different parts of Pangaea shows that the extinction drove a sharp increase in faunal cosmopolitanism, meaning that post-extinction communities became more similar to each other across wide distances than they had been before. In Laurasia, the northern portion of Pangaea, this pattern closely matches global trends. In Gondwana, the southern portion, the picture diverges: biogeographic connectedness spiked abruptly in the latest Triassic and then gradually declined through the Early Jurassic.18PubMed Central. Mass extinctions drove increased global faunal cosmopolitanism on the supercontinent Pangaea
This hemispheric difference is worth thinking about. When a mass extinction removes many specialized, regionally distinct species, the survivors and early colonizers tend to be generalists that spread widely, homogenizing faunas across regions. The fact that Gondwana followed a different trajectory hints at differences in the severity or nature of the extinction between the two halves of the supercontinent, or perhaps at geographic barriers that persisted even on a connected landmass. Researchers are still working out the details, but it is a reminder that even a “global” extinction has local character.
Why This Extinction Gets Less Attention
The end-Triassic event sits in an awkward spot in public awareness. It lacks the dramatic single-cause narrative of the asteroid impact that ended the Cretaceous. It does not have the sheer severity of the end-Permian extinction, which eliminated an estimated 90 percent of marine species. And its biological legacy, while enormous, is subtle: it did not end a charismatic group of animals in one blow but rather cleared the way for one lineage (dinosaurs) to eventually produce the most famous animals in Earth’s history. The extinction is, in a sense, the opening act that nobody remembers.
The science has also been harder to pin down. CAMP lavas are spread across four continents that have since separated, making it difficult to reconstruct the eruption history as a single coherent sequence. Marine boundary sections are rarer and often less complete than those for the end-Permian or end-Cretaceous. And the multi-mechanism kill model, where sulfate aerosols, CO₂, methane, ocean acidification, and anoxia all played roles on different timescales and in different environments, resists the kind of simple explanation that makes for a clean textbook summary. The research community has made major progress in the past two decades, particularly through high-precision dating and geochemical proxies like mercury enrichment, but there is still genuine scientific debate about the relative importance of each kill mechanism and how they interacted.
What is not debated is that the end-Triassic extinction fundamentally restructured life on land and in the oceans. It ended the era of pseudosuchian dominance, launched the age of dinosaurs, and set the stage for the Jurassic ecosystems that would persist for tens of millions of years. Understanding it is essential for understanding how the world that produced Tyrannosaurus, Triceratops, and eventually birds came to exist in the first place.