Around 232–234 million years ago, during the late Carnian stage of the Triassic period, Earth underwent one of its most dramatic climate shifts. This event—known as the Carnian Pluvial Episode (CPE)—marked a period of unusually heavy rainfall lasting around one to two million years, dramatically altering ecosystems both on land and in the sea.
During this interval, Earth’s normally dry landscapes—especially the interior of the then-supercontinent Pangaea—were flooded by persistent monsoon-style rains. Geological records from multiple continents show that what had been arid or semi-arid regions shifted into humid weather regimes.
The reasons for this climatic upheaval appear rooted in massive volcanic activity in what is now Alaska and British Columbia, in the so-called Wrangellia Large Igneous Province. These eruptions released large volumes of greenhouse gases such as carbon dioxide, warming the planet, increasing evaporation from the oceans, and inducing stronger moisture-laden winds and rainfall.
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What triggered the deluge?
The leading explanation for the Carnian Pluvial Episode centres on the Wrangellia flood basalts. These enormous volcanic eruptions around 234–232 million years ago injected greenhouse gases and ash into the atmosphere, altering climate and hydrology.
As global temperatures rose, more water evaporated from the sea and returned as rain. With Pangaea’s configuration creating vast continental interiors, the setup was ripe for strong monsoonal circulation and heavy inland rainfall. Geological evidence—such as thick siliciclastic-rich sediment layers and increased weathering signatures—confirm much higher runoff and precipitation.
Some researchers also point to tectonic uplift (for example the formation of new mountain ranges) as contributing to the shift from arid to wet, by forcing moist air inland. But the volcanic trigger remains the most widely supported cause.
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A world drenched—and transformed
The rainfall surge wasn’t just a weather change—it reshaped entire landscapes, ecosystems and evolutionary trajectories. On land, formerly dry zones turned into lush habitats with lakes, rivers and swamps.
In the ocean, sediment changes show that carbonate platform ecosystems collapsed or transformed, likely due to increased runoff, higher nutrients and shifting chemistry in coastal waters.
The event coincides with the extinction of a significant number of marine species (one study estimates around 33% of marine genera disappeared). At the same time, this crisis appears to have opened ecological space for major evolutionary radiations: conifers and ferns expanded, insects diversified, and notably, the first major rise of dinosaurs and other modern groups got underway.
As one summary puts it, the Carnian Pluvial Episode didn’t just kill—it cleared the way for new life forms to dominate.
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Why it matters today
While the idea of “it rained nonstop for a million years” is a bit of an exaggeration, the key takeaway is that Earth experienced a long-lasting shift to much wetter conditions, which in turn drove deep ecological and evolutionary changes.
For modern readers, the CPE is a powerful reminder of how climate forcing—whether via volcanoes or other mechanisms—can trigger cascading effects across the planet, across ecosystems, and across millions of years. It underscores the interconnectedness of the atmosphere, hydrosphere, lithosphere and biosphere.
If current human-driven climate change prompts similar large-scale shifts (albeit faster), then studying the Carnian Pluvial Episode helps us comprehend what kind of transformations are possible even if the drivers differ.
When the world flooded and forests spread 233 million years ago, it wasn’t a simple rainstorm it was a planetary makeover. The Carnian Pluvial Episode stands out as a turning point: volcanic fury warmed the globe, intensified the hydrological cycle, rained down over lands once dry, triggered extinctions and then enabled the rise of dinosaurs and the modern terrestrial fauna.
In the grand story of Earth, this is the chapter where chaos yields innovation and in that sense, the deluge matters as much as the dinosaurs it helped seed.
Sources:
Dal Corso J. et al., Extinction and dawn of the modern world in the Carnian (Late Triassic). PMC Biol. Rev. (2020).
“Earth endured over one million years of rain in the ‘Carnian Pluvial Event’”, Earth.com (2024).
“Newly discovered mass extinction paved the way for dinosaurs”, ScienceFo
cus (2020).
Wikipedia article: Carnian Pluvial Episode.