What Did Earth Look Like 250 Million Years Ago?

Nearly all of Earth’s land 250 million years ago was locked together in a single supercontinent called Pangaea, surrounded by one immense global ocean. The climate was harsh, dominated by scorching summers and bone-dry interiors. And the planet was either in the throes of, or just emerging from, the worst mass extinction in the history of complex life, a catastrophe so severe it killed off roughly nine in ten marine species and reshaped every ecosystem on the planet.

A Single Supercontinent and a Vast Ocean

If you could look at a globe 250 million years ago, the most striking thing would be how lopsided it seemed. Almost all of Earth’s land had been stitched together over hundreds of millions of years into one enormous C-shaped mass: Pangaea. The northern portion, called Laurasia, included what would eventually become North America, Europe, and Asia. The southern portion, Gondwana, contained the future South America, Africa, India, Antarctica, and Australia. These two halves were joined along their western margins near the equator. Paleomagnetic reconstructions, which use magnetic signals frozen into ancient rocks to determine where those rocks formed, place the most convincing fit of these landmasses in what geologists call the “Pangaea A” configuration.¹

On the eastern side, the two halves separated to form a large embayment called the Tethys Sea, which opened eastward like a massive wedge-shaped gulf. Everything else was ocean. Panthalassa, the global ocean, covered about 70 percent of the planet’s surface, dwarfing even today’s Pacific. With no Atlantic, no Indian Ocean, and no Southern Ocean as we know them, ocean circulation was entirely different. Warm equatorial currents entered the Tethys, but huge stretches of Panthalassa were essentially open water with no nearby landmasses to steer currents the way continents do today.

Megamonsoons and Punishing Heat

Concentrating nearly all land into one block created a climate that was, by modern standards, extreme. Climate simulations of Pangaea consistently show intense “megamonsoons” driven by the sheer size of the continent. In summer, the vast interior baked under the sun, drawing moisture-laden winds inland from the Tethys and generating powerful seasonal monsoon systems. In winter, the pattern reversed, with cold, dry air flowing outward from the continental interior. The result was dramatic seasonal swings and widespread aridity across most of the supercontinent’s interior, with year-round or seasonally wet conditions limited to the eastern coasts, the tropical western coastline, and regions above about 40 degrees latitude.²

Think of the most extreme continental climate you know and multiply it. Interior Pangaea would have made central Asia feel temperate by comparison. Summers were brutally hot, winters surprisingly cold for many latitudes, and moisture simply could not penetrate far enough inland to sustain lush vegetation across most of the landmass. Vast red-bed deserts, evaporite deposits, and sand dune formations preserved in the rock record confirm what the models predict: much of Pangaea’s interior was desert or semi-arid scrubland.

Life Before the Crisis

Despite the harsh interior, the edges and higher latitudes of Pangaea supported rich ecosystems. In the southern reaches of Gondwana, including what is now South Africa, South America, Australia, India, and Antarctica, one of the most extensive and long-lived forest biomes in Earth’s history flourished. These forests were dominated by glossopterid gymnosperms, seed plants with distinctive tongue-shaped leaves that carpeted enormous swaths of the southern hemisphere. Their peat-forming capacity was immense, producing thick coal seams that still underlie parts of these continents.³

On land, the dominant large animals were not dinosaurs (those would come later) but synapsids, a group more closely related to mammals than to reptiles. The most ecologically prominent synapsids included bulky herbivores called dicynodonts, stocky creatures with beaked jaws and, in many species, a pair of tusks. Among these, the genus Lystrosaurus would become one of the most famous survivors of the coming catastrophe, but in the late Permian it was just one of many dicynodonts in a diverse community of predators, prey, and scavengers. Archosauromorphs, the lineage that would eventually give rise to dinosaurs, crocodilians, and birds, were present but obscure, far from dominant.⁴

In the oceans, the late Permian hosted diverse reef systems, brachiopod-rich seafloors, and thriving communities of crinoids, bryozoans, and foraminifera. These were overwhelmingly Paleozoic-style ecosystems, fundamentally different in character from the mollusk-and-fish-dominated seas that came afterward.

The Siberian Traps and the Trigger

What turned this world upside down was volcanism on a scale almost impossible to visualize. In what is now Siberia, a massive outpouring of lava known as the Siberian Traps Large Igneous Province began erupting right around 252 to 250 million years ago. This was not a single volcano but a flood of basaltic lava that eventually covered up to 5 million square kilometers, an area roughly the size of the European Union.⁵ The main pulse of eruption was geologically brief, perhaps tens of thousands to a few hundred thousand years, but its environmental consequences cascaded globally.

The eruptions did not just pour lava. The magma intruded through vast deposits of coal, limestone, and salt in the Siberian crust, releasing enormous quantities of carbon dioxide, sulfur dioxide, and halogen gases. These emissions altered the chemistry of the atmosphere and oceans in ways that proved lethal. Mercury anomalies found in sedimentary rocks from sites nearly antipodal to Siberia, in South Africa and Australia, demonstrate that the volcanic fallout reached the farthest corners of Pangaea through long-distance atmospheric transport.⁶ Mercury concentration peaks found globally near the extinction boundary confirm a tight coupling between the volcanic activity and the die-off.⁷

An Ocean Losing Its Oxygen

The oceans at 250 million years ago were in deep trouble. As volcanic CO₂ warmed the planet, ocean circulation slowed and the water’s capacity to hold dissolved oxygen dropped. Uranium isotope data from marine sediments show a roughly sixfold increase in the area of oxygen-starved ocean floor compared to pre-extinction conditions.⁸ In many areas, the water column did not just lose oxygen; it became euxinic, meaning that toxic hydrogen sulfide built up in the water. Biomarker evidence from Australia and South China shows that this sulfide-rich water reached all the way up into the sunlit zone where photosynthesis normally sustains marine life.⁹

The mechanism connecting volcanism to this ocean-wide oxygen crash involved nutrients, particularly phosphorus. Enhanced weathering driven by volcanic warming flushed phosphorus from rocks on land into the sea, fueling blooms of marine algae and microorganisms. As these organisms died and sank, their decomposition consumed oxygen. Under normal conditions, iron minerals in the sediment would have locked up much of the recycled phosphorus, keeping things in check. But as conditions tipped from simply low-oxygen to sulfide-rich, the iron chemistry changed, releasing phosphorus back into the water and creating a runaway feedback loop that spread anoxic conditions across large portions of continental shelves.¹⁰

On top of the suffocation, the oceans were also acidifying. A rapid injection of carbon drove an abrupt acidification event that preferentially killed marine animals with heavy calcium carbonate skeletons, including many reef builders.¹¹ Between oxygen loss, sulfide poisoning, acidification, and warming, the seas around 250 million years ago were hostile to complex life in a way that has no parallel in Earth’s more recent history.¹²

Warming Seas and Spiking Temperatures

The warming itself was severe. Oxygen isotope measurements from fossils preserved in late Permian and earliest Triassic rocks in South China indicate that tropical surface waters warmed by about 8°C in the latest Permian.¹³ Data from Iran tell a similar story: tropical sea surface temperatures that had been in the range of 27 to 33°C during the final stage of the Permian spiked to over 35°C at and just after the extinction boundary.¹⁴ For context, modern tropical sea surface temperatures average around 27 to 29°C. Water above 35°C is physiologically lethal for many marine organisms, including many fish and invertebrates. The warming alone would have made large swaths of the tropical ocean uninhabitable.

An Ozone Shield Under Siege

One of the more insidious consequences of the Siberian Traps eruptions played out in the upper atmosphere. The volcanic emissions appear to have damaged Earth’s ozone layer, exposing life on land and in shallow water to elevated ultraviolet-B radiation. Multiple sulfur isotope signatures from the extinction interval fingerprint intense UV irradiation of volcanic sulfur dioxide in the atmosphere, a signal that requires significant disruption of the ozone shield.¹⁵ Direct evidence comes from spore and pollen records, which show a spike in malformed and UV-damaged grains coinciding precisely with mercury spikes and carbon cycle disruptions tied to the eruptions.¹⁶

Laboratory experiments on living conifers exposed to UV-B levels matching the estimated end-Permian regime showed that pollen malformation rates increased fivefold. The trees survived the radiation but were rendered sterile, unable to reproduce.¹⁷ Forests did not necessarily burn or die immediately; they simply stopped regenerating. This is a chilling mechanism for deforestation that left no obvious scars in the wood but effectively killed forests within a generation. At low latitudes, evidence also points to sustained wildfire activity coinciding with the onset of terrestrial ecosystem collapse, suggesting that fire and UV stress worked in tandem to strip vegetation from the land.¹⁸

The collapse of the great glossopterid forests of the southern hemisphere was one of the most visible losses. The peat-forming ecosystems that had built thick coal deposits for tens of millions of years vanished entirely. No coal was deposited anywhere on Earth during the entire Early Triassic, a gap of roughly seven million years, and Permian-level plant diversity and peat thickness did not recover until the Late Triassic, about 230 million years ago.¹⁹

Animals at the Boundary

On land, the extinction reshaped vertebrate communities dramatically. Among the survivors, Lystrosaurus stands out as one of the most iconic. This tusked, pig-sized herbivore became enormously abundant in the earliest Triassic, dominating post-extinction fossil assemblages in South Africa and elsewhere.²⁰ In the Karoo Basin, the way Lystrosaurus is preserved changes across the boundary: late Permian fossils tend to be isolated skulls and scattered bones, while earliest Triassic specimens are frequently found as articulated, curled-up skeletons or packed into mass-death bonebeds, suggesting highly seasonal, drought-prone conditions that killed animals in groups.²¹

The previously marginal archosauromorphs began their ascent during this interval. The post-extinction world started with a morphologically conservative “disaster fauna” of low diversity. Over the next few million years, evolutionary rates spiked significantly, and by about five million years after the extinction, archosauromorphs had undergone a dramatic increase in species counts, body forms, and ecological roles, laying the groundwork for the age of dinosaurs.⁴

A Shrunken World and Slimy Seas

One of the strangest features of the world at and just after 250 million years ago is that everything got smaller. Body fossils and trace fossils from the earliest Triassic are conspicuously tiny compared to those in both older and younger rocks. The smallest sizes appear right at the extinction boundary and persist through the earliest stages of the Triassic, a pattern researchers call the Lilliput effect.²² Across ecologically and physiologically different marine groups, both maximum and median species sizes dropped sharply from the latest Permian into the earliest Triassic, then gradually recovered over the next several million years.²³ Whatever was driving conditions in those earliest Triassic seas, it favored small, fast-reproducing organisms over large, specialized ones.

With most complex reef builders dead and burrowing animals decimated, the ocean floors looked profoundly different. Microbial mats, the slimy photosynthetic films that had dominated shallow seas billions of years earlier in the Precambrian, made a dramatic comeback. Freed from competition with complex animals, these mats built widespread structures called microbialites, including stromatolites and thrombolites, across shallow marine shelves around the Tethys and beyond.²⁴ The resulting seascape was, in a sense, prehistoric even by Permian standards. Carbonate platforms that had been built by diverse fossil-rich limestones in the Permian transitioned to an “anachronistic” world of microbial structures and chemical precipitates more reminiscent of Earth’s earliest oceans than of anything the previous several hundred million years had produced.²⁵

Why Recovery Took So Long

The extinction itself was geologically fast, but recovery was agonizingly slow. The entire Early Triassic, a span of about five million years, is characterized by depressed biodiversity and repeated environmental disruptions. Research points to three overlapping reasons for the delay: extreme conditions, including ongoing volcanic activity, persisted well after the initial crisis; the surviving species tended to be generalists and opportunists rather than the specialists needed to rebuild complex food webs; and the resulting ecosystems were fragile, poorly structured, and vulnerable to further disruption.²⁶

The microbialites that blanketed shallow seas persisted in part because the normal ecological checks on microbial growth, particularly grazing by animals and competition for space, had been removed by the extinction.²⁷ The Lilliput effect in marine animals lasted through the earliest Triassic before body sizes began to rebound. On land, the coal gap persisted for millions of years. The planet was not simply bouncing back from a single bad event; it was stuck in a degraded state, repeatedly disturbed, and slowly building its way back to ecological complexity.

Freshwater Ecosystems as a Refuge

Not every habitat was equally devastated. Freshwater environments appear to have served as relative refuges during the crisis. Temnospondyl amphibians, large-headed creatures that occupied ecological roles similar to modern crocodilians and giant salamanders, experienced a burst of success in the Early Triassic. Their diversity was low during the Permian, but both the number of species and the range of skull shapes increased across the extinction boundary and continued to climb in the early Triassic.²⁸

The key to temnospondyl success seems to have been a generalist feeding strategy and the relative stability of the freshwater food web. While strictly land-based predators struggled with scarce and unpredictable prey, temnospondyls could exploit a wide variety of food in rivers, lakes, and floodplains. Their body shapes changed little through the extinction itself, suggesting they did not need radical adaptation to survive. Some lineages experienced a temporary size reduction in the immediate aftermath, but pre-extinction body sizes were restored within a million or two years.²⁹ Freshwater, in other words, kept running even when the world above and around it was falling apart. The success of these aquatic amphibians hints that how an organism was connected to the food chain mattered as much as raw toughness in determining who survived the worst extinction Earth has ever seen.