Name: That Time It Rained for Two Million Years
Uploaded: 2021-05-01T10:09:14.000Z
Duration: 8 min 4 s
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Imagine a world so warm that the ocean feels like a hot tub.

Huge volcanic eruptions have pumped the air full of globe-warming carbon dioxide.

And with the continents locked together from pole-to-pole in the supercontinent of Pangea,

the world is hot, flat, and very, very dry.

Early reptiles and mammal ancestors thrive in this sweltering land, dominating a landscape

that's still struggling to recover from the Permian extinction.

This is Earth, 250 million years ago, at the beginning of the Triassic Period.

But then, starting around 234 million years ago, the climate suddenly changed, for the

The rains finally came to this hot, dry world.

And then they stayed … for two million years.

This period of intense rain killed off many of the early reptiles and … confused the

heck out of the geologists who found the flood deposits millions of years later.

This time is known as the Carnian Pluvial Episode, and it set the stage for a new group

Evidence of just how hot and dry the world was at the start of the Triassic is trapped

Rocks from that period are mostly swaths of red sandstones and soil deposits from dry

woodlands, with no sign of the coal swamps that had covered the world during much of

And one major reason that the world was so dry was the shape of Pangea.

With all the continents locked together, rain clouds couldn't move much past the coastlines,

and there were no big mountain ranges to break up the low, arid land.

Now, dinosaurs did exist in this dry, post-Permian world.

But they were still vying for their place among early reptiles and reptile-like mammal

The dominant carnivores back then were the early crurotarsans, a broad group of croc-like

animals that included reptiles like pseudosuchians and phytosaurs.

For example, there was Ornithosuchus, which had long hind legs and could actually stand

up when it wanted to run, which I imagine would've been both awesome and terrifying to

But even stranger than these were the rhynchosaurs, herbivores with parrot-like beaks and, sometimes,

cheekbones to die for, all on a chubby lizard body.

And although there were no true mammals, there were dicynodonts -- the closest things to

They're actually more closely related to us than, say, Dimetrodon, despite being scaly,

four-legged creatures with bills and tusks.

All of these fascinating creatures were widespread for most of the Triassic, with one species

of dicynodont – called Lystrosaurus – being so common all over the world that its fossils

were actually used to help construct the idea of Plate Tectonics

But these animals, adapted as they were to life in a dry climate, were in for a big shakeup.

Most of what we know about the history of the climate comes from plant fossils and rock

And in the early 1990's, two British geologists found rocks that didn't match the dry climate

Instead of finding red, slowly-deposited sand, they found thick layers of river rocks, sediments

from giant lakes, and evidence of coal swamps.

All of these were signs of massive rainfall, over the course of some two million years.

But stranger still, these traces of a suddenly wet climate turned out to be everywhere, from

England to the Americas to Israel, in regions that were far apart at the time.

That meant the rise in rainfall must have been world-wide.

Initially, other geologists were skeptical.

Couldn't these rocks just be explained by a lot of big local floods?

Well, over the next two decades, reports of more and more weird rocks kept trickling in,

and they kept pointing to a world that was getting wetter and wetter.

The rocks revealed coal deposits in Austria, traces of ancient lakes in Italy, wet soils

And they all dated to the same window of time -- between 232 and 234 million years ago.

In time, this phenomenon came to be known as the Carnian Pluvial Episode, or CPE.

The Carnian is the name of the geologic age within the Triassic when this all happened.

And for what it's worth I seriously thought about naming this episode the Chronicles of Carnia

but I didn't because that would have been dumb.

And “pluvial” means rain, and it rained a whole awful lot.

For example, one estimate suggests that the average annual rainfall in what's now Utah

almost quadrupled, reaching a peak of 1400 millimeters, or about 55 inches of rain a year.

For context, that's how much that a temperate rainforest gets today, like say, in the Pacific

And this would have happened over, and over, and over again, all around the world.

It was not one big flood; it was more like floods every year, all over the place, for

And with all this rain, things were bound to change - and one of the biggest changes

In rock dated to the start of the Carnian Pluvial Episode, dinosaurs account for about

5% of the fossils of terrestrial vertebrates.

But by the end, they make up more than 90% of those fossils.

So what made the dinosaurs so suddenly successful?

Were they better off than their competitors in this newly wet world?

Or did other animals simply die, leaving them to rule the world by default?

The key might not have been the rain itself, but what the rain brought with it: a proliferation

During this time, we begin to see lots of large conifers, and big coal-forming plants,

like the primordial-looking Bennettitales.

For herbivores, this change in food supply could have been a game changer.

For example, rhynchosaurs were abundant, but they were also … short.

And they couldn't stand on their hind legs to reach higher leaves.

This would've been fine in a dry environment, where plants tend to stay close to the ground.

But in a wet forest, rhynchosaurs would've only been able to eat smaller plants, or whatever

Meanwhile, dicynodonts were herbivores, too, but they didn't have teeth.

And, they also didn't use gastroliths, the rocks that some animals - like birds - swallow

Without teeth or gastroliths, dicynodonts would have had a hard time eating anything

And sure enough, fossils of dicynodont poop from this time have been found to contain

the digested remains of mostly soft ferns, with only very small amounts of wood.

By comparison, some plant-eating dinosaurs - which had both teeth and gastroliths - left

So as the climate became wetter, soft small ferns were quickly replaced by tall woody

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That Time It Rained for Two Million Years

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