Artistic representation of a Middle-Late Triassic landscape of southern Brazil. A large Prestosuchus chiniquensis feeds on the carcass of a dicynodont while individuals of Parvosuchus aurelioi compete for scraps. Credit: Wikimedia Commons
It’s often called “the time it rained for two million years.” That’s not quite right, but the real story may be even stranger.
Around 234 million years ago, Earth entered a long, uneven climate crisis known as the Carnian Pluvial Episode. For roughly one to two million years, parts of the supercontinent Pangea swung from dry to intensely wet. As rainfall surged, rivers grew bigger and soils weathered faster. This affected many ecosystems across the planet.
And when the turmoil passed, dinosaurs were kings.
Dinosaurs had already evolved before this event, but the Carnian crisis seems to have changed the world around them. It affected their competitors and broke existing food webs. In the chaos, dinosaurs found room to expand.
A Gray Stripe
The first clues were easy to miss.
In Britain, geologists Alastair Ruffell and Michael Simms studied the famous red rocks of the Triassic. Running through them was a grey band—the kind of sediment that shouldn’t exist in a desert-like world. These rocks had formed in a mostly arid world, yet this layer hinted at wetter conditions.
Other clues turned up elsewhere. In the Eastern Alps, researchers found pulses of sediment interrupting carbonate rocks. In plain English, this means rivers and runoff had suddenly become much more active. Similar signs have since been reported from regions including Europe, China, South America, and beyond.
Together, the rocks pointed to a major climate shift. Pangea had been mostly dry, then parts of it turned suddenly wetter. The phrase “it rained for two million years” gets the idea across, but oversells it. The evidence suggests repeated bursts of humid weather and heavy rainfall over roughly one to two million years.
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Together, the rocks pointed to a major climate disruption. Pangea, the supercontinent that concentrated most of the planet’s landmass, wasn’t exactly a swamp. But across many regions, dry Triassic landscapes were repeatedly interrupted by bursts of humidity and heavy rainfall. Rain had come, and this surprised geologists.
“The Carnian is a real problem,” paleontologist Paul Olsen told Discover. “We don’t know it well.”
Volcanoes Behind the Rain
The leading suspect is a vast volcanic province called Wrangellia, remnants of which are now found in Alaska and British Columbia.
During the Carnian, there were massive volcanic eruptions. These eruptions pumped huge amounts of carbon dioxide into the air. That gas warmed the planet through the greenhouse effect. In turn, this meant warmer seas evaporated more water, moist air moved inland over Pangea, and monsoons unloaded heavy rains. These may have been some of the strongest rains our planet ever witnessed.
“The eruptions peaked in the Carnian,” Jacopo Dal Corso, of the China University of Geosciences, explained. “I was studying the geochemical signature of the eruptions a few years ago and identified some massive effects on the atmosphere worldwide. The eruptions were so huge, they pumped vast amounts of greenhouse gases like carbon dioxide, and there were spikes of global warming.”
A 2024 study from North China found four separate pulses of increased chemical weathering—the breakdown of rocks by warm, wet conditions—tied to volcanic signals and carbon-cycle disturbances during the Carnian Pluvial Episode.
Rain, in other words, was only the visible symptom. Beneath it was a whole Earth system convulsing.
Extinction Opens Another Door
Credit: Pexels
The Carnian was brutal, and most creatures living at the time would have struggled with the change
Acid rain may have stripped soils and battered plants. More rain meant more erosion, and rivers poured sediment and nutrients into lakes and seas, changing the waters’ chemistry. A 2020 study estimated that about 33% of marine genera disappeared during the crisis.
But some groups seemed to relish this opportunity.
“The new floras probably provided slim pickings for the surviving herbivorous reptiles,” said Professor Mike Benton from the University of Bristol. “We now know that dinosaurs originated some 20 million years before this event, but they remained quite rare and unimportant until the Carnian Pluvial Episode hit. It was the sudden arid conditions after the humid episode that gave dinosaurs their chance.”
On land, large herbivores and plant communities morphed. Dinosaurs, still in their infancy, were among the animals that expanded after the upheaval. A 2018 study linked the Carnian wet interval to a sharp rise in dinosaur diversity, abundance, and geographic spread.
It’s not that the dinosaurs like the rain. It’s more that the Carnian changed the rules of the game. Early dinosaurs weren’t the ecosystem dominators we know today. Initially, they struggled to make a mark on their ecosystem. But when the ecosystems were disturbed and food webs were reshuffled, dinosaurs found openings that previous groups no longer held.
By the Jurassic and Cretaceous, their descendants would dominate the land.
A Muddy Reset
The Carnian Pluvial Event also appears to have helped shape lineages that still surround us. Studies connect this interval with the rise or early diversification of major groups, including turtles, crocodilians, lizards, amphibians, mammal relatives, and the dinosaur line that eventually gave rise to birds.
In the oceans, modern-like coral reefs and plankton communities also gained traction after the crisis. The turnover helped replace older reef builders with the coral groups that would become more familiar in later seas. Tiny plankton also diversified, reshaping marine food webs from the bottom up.
But some scientists warn that the dates are still too fuzzy in many places to prove that all wet layers formed at the same time. Others see the Carnian as one of life’s great hinge moments.
“So far, palaeontologists had identified five ‘big’ mass extinctions in the past 500 million years of the history of life,” Jacopo Dal Corso from the China University of Geosciences added. “We have identified another great extinction event, and it evidently had a major role in helping to reset life on land and in the oceans, marking the origins of modern ecosystems.”
Both views can be true. The rocks do not tell a simple comeback story. They show a messy pattern: climate stress wiped out many species, and the survivors expanded into the space left behind.