Permian

• 1. Introduction

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  The Permian is a geologic period stretching 47 million years, from the close of the Carboniferous to the dawn of the Triassic, and it ended with the single greatest catastrophe life on Earth has ever faced. Nearly 81% of marine species vanished. Roughly 70% of all land creatures disappeared. Scientists call it the Permian-Triassic extinction event; in popular geology it goes by a starker name: the Great Dying. But before that catastrophe, something remarkable was underway. A single landmass called Pangaea dominated the planet. New kinds of animals were stepping into the light. The ancestors of every mammal alive today were diversifying rapidly. And a geologist named Sir Roderick Murchison had not yet given any of this a name. What shaped those 47 million years? And how did a period so rich in life end so completely?

• 2. Naming the Rocks

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  Sir Roderick Impey Murchison, president of the Geological Society of London, traveled to Russia in 1840 and 1841 alongside the French geologist Edouard de Verneuil. Their destination was the vicinity of the Ural Mountains, and what they found there changed the map of deep time. Murchison identified what he described as a "vast series of beds of marl, schist, limestone, sandstone and conglomerate" stacked above Carboniferous strata. He named the whole sequence after Perm, the surrounding Russian region, which in turn took its name from the medieval kingdom of Permia that had occupied the same territory centuries before. The name entered geology formally in 1841. Before Murchison coined the term, rocks of equivalent age had gone by different names in different countries: the Rotliegend and Zechstein in Germany, the New Red Sandstone in Great Britain. Murchison brought those scattered formations under a single concept. Between 1853 and 1867, the American geologist Jules Marcou identified Permian strata across a vast stretch of North America, from the Mississippi River to the Colorado River, and proposed the alternative name Dyassic. Murchison rejected it in 1871. Even so, controversy persisted: the United States Geological Survey did not fully accept the Permian as its own period, distinct from the Carboniferous, until 1941, a full century after Murchison's original paper. Today three of the world's most Permian-rich regions are the Ural Mountains where Perm itself sits, China, and the American southwest, including the Texas red beds and the Permian Basin spanning Texas and New Mexico.

• 3. One World, One Ocean

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  Pangaea straddled the equator and reached toward both poles during the Permian, making it the defining geographic fact of the period. It had assembled through the collision of two earlier landmasses, Euramerica and Gondwana, during the preceding Carboniferous. A single vast ocean, called Panthalassa, wrapped around it. Between Asia and Gondwana lay the Paleo-Tethys Ocean, which was actively shrinking as the Cimmeria continent rifted away from Gondwana and drifted north toward Laurasia. In its place, a younger ocean was opening on the southern end: the Neotethys, which would go on to shape much of the geography of the Mesozoic Era. The Central Pangean Mountains, formed from the same Carboniferous collision that built Pangaea, reached their peak height around 295 million years ago, comparable to the modern Himalayas, before erosion gradually wore them down across the remainder of the Permian. In what is now northwestern Europe, a hypersaline epicontinental sea called the Zechstein Sea spread across the landscape. By the very end of the Permian, additional crustal blocks had fused onto Pangaea: the Kazakhstania block collided with Baltica during the Cisuralian, while the North China Craton, the South China Block, and Indochina all joined together and merged with Pangaea before the period closed.

• 4. Fire, Ice, and Drying Air

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  The Permian opened while Earth was still in the grip of the Late Paleozoic Ice Age, a glaciation that had begun in the latest Devonian and lasted through the entire Carboniferous. Temperatures initially continued to cool through the early Asselian and Sakmarian stages, when the ice age reached its peak. Then, by around 287 million years ago, a warming pulse called the Artinskian Warming Event caused the South Pole ice cap to retreat, though glaciers clung to the uplands of eastern Australia and possibly to the mountainous far north of Siberia. A cool interval returned in the late Kungurian and stretched into the early Capitanian, followed by a distinct cool phase lasting roughly 3-4 million years known as the Kamura Event. The Kamura Event was then broken by the Emeishan Thermal Excursion around 260 million years ago, driven by the eruption of the Emeishan Traps. That rapid climate shift was directly associated with the Capitanian mass extinction event. The last Australian glaciers melted during the late Wuchiapingian, marking the end of the Late Paleozoic Ice Age altogether. Then came the final blow. The eruption of the Siberian Traps at the Permian-Triassic boundary released more than 5 teratonnes of CO2, more than doubling the atmospheric concentration of carbon dioxide. A shift of negative 2% in oxygen-18 isotope ratios marks the extreme scale of that climatic disruption. Across much of the Permian, a planetary megamonsoon dominated the interior of Pangaea, producing intense aridity and extreme seasonal swings. Evidence for this megamonsoon survives in the Qiangtang Basin of Tibet, where ancient megamonsoonal rainforests have been identified, and in the sedimentary record of the Sydney Basin in Australia.

• 5. Rise of the Amniotes

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  Synapsids, the group that would eventually give rise to mammals, flourished across the Cisuralian. Among them were large and distinctive animals: Dimetrodon, familiar from its prominent sail-like back, belonged to the carnivorous sphenacodontid pelycosaurs that dominated early Permian North America and Europe alongside herbivorous edaphosaurids. Their ability to cope with drying conditions gave amniotes a decisive edge over the amphibians that had ruled the Carboniferous. A major faunal turnover then unfolded across the transition from the Cisuralian into the Guadalupian, as pelycosaurs gave way to more advanced therapsids over a period of roughly 20 million years, from the Sakmarian through the end of the Kungurian. Whether a discrete extinction event drove this turnover, sometimes called Olson's Extinction, or whether it was a gradual replacement, remains debated; a gap in the terrestrial fossil record during the late Kungurian and early Roadian, known as Olson's Gap, obscures the picture. By the Middle Permian, the faunas of South Africa and Russia were dominated by therapsids, especially the diverse Dinocephalia. Dinocephalians vanished entirely at the end of the Middle Permian during the Capitanian mass extinction. Late Permian faunas were then ruled by predatory sabertoothed gorgonopsians, herbivorous beaked dicynodonts, and large pareiasaur parareptiles. Cynodonts, the therapsid lineage ancestral to all modern mammals, first appeared during the Late Permian and achieved a worldwide distribution before the period ended. The Weigeltisauridae, an extinct lizard-like reptile family from the Late Permian, possessed extendable wings similar to modern gliding lizards and represent the oldest known gliding vertebrates.

• 6. A World of Insects and Plants

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  Insects that first appeared during the Carboniferous diversified dramatically during the Early Permian. By the start of the period, a coevolutionary arms race between insects and plants was already well underway, preserved in fossilized insect damage on plant tissue and defensive structures in plant reproductive organs. Among the dominant insects of the Permian were early Paleoptera, Polyneoptera, and Paraneoptera. A group called Grylloblattidans, winged insects thought to be relatives of modern ice crawlers, reached their greatest diversity during the Permian, representing as much as a third of all insects at some fossil sites. Mecoptera, sometimes called scorpionflies, first appeared during the Early Permian; some Permian mecopterans from the family Mesopsychidae had long proboscises suggesting they may have pollinated gymnosperms. The earliest known beetles appeared at the beginning of the Permian; early forms such as Permocupedidae likely fed on decaying wood, while several later lineages expanded into aquatic habitats by the Late Permian. On land, plants were undergoing their own transformation. The swamp-loving lycopod trees of the Carboniferous, including Lepidodendron and Sigillaria, gradually gave way in continental interiors to seed ferns and early conifers. The oldest likely record of Ginkgoales is Trichopitys heteromorpha from the earliest Permian of France. The earliest fossils definitively belonging to modern cycads come from the Late Permian. In Cathaysia, the equatorial island chain that would later become South China, lycopod swamps reminiscent of the Carboniferous flora survived right to the close of the Permian, while the Gondwanan south was blanketed in Glossopteris seed fern forests whose ecology has been compared to that of modern bald cypress.

• 7. The Great Dying

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  Trilobites had patrolled Earth's oceans since the Cambrian, surviving every earlier catastrophe, yet they vanished before the Permian was out. The Permian-Triassic extinction event removed 90-95% of marine species and 70% of all land organisms. It stands as the only known mass extinction that also swept away a major portion of insect diversity. Flood basalts poured from what is now the Siberian Traps for thousands of years. One calculation suggests the worst-case scenario from those eruptions alone could have raised global temperatures by five degrees Celsius. A separate hypothesis invokes the ocean venting of hydrogen sulfide: oxygen-depleted deep water allows anaerobic bacteria to generate the gas, and if it accumulates sufficiently and rises into the atmosphere, it could destroy the ozone layer and expose surviving organisms to lethal ultraviolet radiation. A third hypothesis builds on the warming scenario, proposing that a five-degree temperature rise could have warmed the oceans enough to melt frozen methane reservoirs below the seafloor near coastlines, releasing one of the most potent greenhouse gases in a secondary pulse. The pattern of extinctions in the boundary layer lends some support: a first land-based phase of die-offs, then a marine-based phase coinciding with a spike in carbon-12 levels, then a third land-based phase. Ecosystems on land required 30 million years to recover from the catastrophe. Among the survivors, nautiloids, a subclass of cephalopods, came through the event despite the devastation around them, and the Archosauromorpha, the reptile lineage destined to produce dinosaurs and pterosaurs, had already appeared during the Late Permian and would come into their own in the world that followed.