Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Wednesday, June 7, 2023

The long rain

Imagine going back 240 million years.

This would land you in the early Triassic Period.  By this time, the Earth would have had twelve million years to recover from the cataclysmic Permian-Triassic Extinction, the largest mass extinction on record.  Life had rebounded some -- two of the dominant terrestrial animal groups were the terrifying crurotarsans (picture a long-legged on-land crocodile) and the dicynodonts (which looked a little like a rhino with a parrot's bill -- and tusks).

Finding your way around the place would be confusing, if all you know is the current continental arrangement.  Pangaea was still locked together, and would be until rifting began to open up the Atlantic Ocean -- but that was still forty million years in the future.

[Image licensed under the Creative Commons Fama Clamosa, Pangaea 200Ma, CC BY-SA 4.0]

Because virtually all the land masses of the world were jammed together into one supercontinent, the climate was really dry.  There probably was a reasonable amount of rainfall along the coastline, but most places were very far away from the coast.  The result is that one of the major early Triassic sedimentary rocks is the "Triassic red sandstone" formed from wind-blown layers of sand deposited in conditions that resembled today's Sahara Desert.  But instead of being restricted to a part of a single continent, this was what it was like in the interior of Pangaea -- i.e., the entire land mass on planet Earth.

But even the Sahara isn't lifeless, and neither was the continental interior of Pangaea during the early Triassic.  Organisms found a way to cope with the dry conditions, and -- all things considered -- life was doing okay.

Then -- 234 million years ago -- it started to rain.

I'm not talking about your short-lived desert thunderstorm, here, nor even the kind of "atmospheric river" event that hit the Central Valley of California this year, causing not only flooding but an explosive burst of wildflowers.

This rainstorm lasted two million years.

It's called the "Carnian Pluvial Episode," and evidence for it can be seen in a sudden shift in sedimentary geology, a change in the isotope concentrations in carbonate rocks (like limestone), and a huge spike in heavy elements (like osmium and mercury) that are much more common in deep-mantle rocks.  The last bit is a clue to what happened -- there was a massive eruption called the Wrangellia Flood Basalts in what would eventually become southern Alaska and western British Columbia.  I've written before about two other flood basalt provinces, the Siberian Traps (implicated in the Permian-Triassic Extinction) and the Deccan Traps (contributory to the Cretaceous Extinction), and while the Wrangellia event isn't as big as either of those, it is many orders of magnitude larger than anything you probably picture as a volcanic eruption.  The Wrangellia Flood Basalt injected huge quantities of carbon dioxide into the atmosphere, largely through the lava burning through limestone, coal, and any organic matter on the surface.  This spiked the atmospheric temperature, increased seawater evaporation...

... and it started to rain.

Imagine being an animal adapted to living in Arizona, and all of a sudden, you find you're living in the Amazon lowlands.  That's pretty much what happened.

The result was another extinction.  Both the crurotarsans and dicynodonts bit the dust.  Or actually, at that point, the mud.  Let me emphasize that both groups were doing fine before the climatic shift; but having spent millions of years adapting to the early Triassic desert conditions, they couldn't handle it when the long rain started.

The winners here were the animals that had the flexibility to cope with the changing conditions -- in this case, dinosaurs, which would go on to dominate the place for another 165 million years.  The early mammals also made it, obviously, but they were still small at this point (and would remain so until the non-avian dinosaurs met their demise).  Interesting that the quintessential Mesozoic group, the dinosaurs, might never have taken off like they did if it hadn't been for a sudden geological event that triggered a climatic shift and knocked out the two main competitor groups.

And I would be remiss if I didn't mention that the rate at which the Wrangellia Flood Basalts injected carbon dioxide into the atmosphere is thought to be significantly smaller than the rate we're doing the same from burning fossil fuels.

Any wonder why environmentalists are worried?

We've already had our share of bizarre weather in the last few years; it seems like not a week goes by without my hearing someone say, "This hardly ever happens."  At the moment, here in upstate New York, it hasn't rained for a month, and we're getting spectacular sunsets (and difficulty breathing) because of a pall of wildfire smoke that's come all the way from central Quebec.  Vietnam and Laos have already set record high temperatures this year, reaching a devastating 44 C (with correspondingly high humidity), as did the Pacific Northwest of the United States, with Portland at a less dangerous but still scorching 35 C.  

Weather isn't climate, something I feel obligated to remind the climate change deniers every time we have a cold snap in January; but as anomalous weather happens over and over and over, these kinds of patterns begin to add up to something significant.  As a Louisiana native, I'm already worried about this year's hurricane season -- especially given that the most recent sea surface temperatures are (in the words of Australian climatologist Matthew England) "heading off the charts."

To judge by the geological record of events like the Carnian Pluvial Episode, it looks like we might be in the last half of "fuck around and find out."


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