Oh, how I struggled with this particular Accretionary Wedge topic:

What geological concept or idea did you hear about that you had no notion of before (and likely surprised you in some way).

I mean, there's a lot. All the hijinks that go on in subduction zones constantly astonish me. The idea that rocks in the mantle flow without being actually molten, and that rocks have any sort of elasticity to begin with – I found that incredible. I had no idea when I first started studying geology just what temperature and pressure could do to minerals. I mean, I knew there was such a thing as a metamorphic rock, but my eyes popped when I learned more of the details. It seems like every time I read a book on geology, there's something new and astonishing.  For instance: whilst reading a book about caves for a bit of the world I'm building, I found out there are places in the world with natural caves formed in salt. I had no idea that happened.

So yes, I'm spoiled for choice.  But I think the one thing that's made my eyes pop the most is the idea that plate tectonics affects climate.

That shouldn't have taken me by surprise, but it did. Sure, I knew about rain shadow effects – I grew up in the American Southwest, which is deep in the rain shadow of the Sierra Nevada. After I moved to Washington State, I drive across a dramatic example of rain shadow within a couple of hours.  Here's the western side of the Cascades, near Seattle:

Image shows a valley full of lush green conifers and deciduous trees. A jagged mountain range rises in the distance, creating its own cap of clouds against the blue sky.
The Cascades viewed from Lord Hill near Monroe, WA. Credit: Dana Hunter

And here's the eastern side, near Vantage:

Image shows me dressed in a blue tank top and black shorts, standing on top of an enormous, rounded chunk of columnar basalt. There is another chunk behind me. Both are about the size of garden sheds. There is a sagebrush-covered flat behind us, with a river gorge cutting through it.
Erratic boulder on Babcock Bench at Frenchman Coulee. Credit: Dana Hunter

That's a profound difference between one side of the mountains and the other, people.

So yes, I knew mountains had a huge affect on climate. And I also knew that where you are in the world matters. Washington State, for instance, would be a much different place if it straddled the Equator. But for some reason, I didn't carry that idea to its logical conclusion: that as the continents go sailing around the world due to the vagaries of plate tectonics, they change everything.

In the first place, plate tectonics creates these mountains that have such an impact on local and regional climates. And haven't I heard that the Himalaya may have changed the world? All because India decided to take a quick trip north and didn't watch where it was going.

As continents move, they affect ocean circulation. And ocean circulation affects global climate. Could you imagine what would happen if some bit of land deflected the Antarctic Circumpolar Current?  You don't have to imagine it all by yourself - go play with a paleoclimate animation and watch the climate change. Look at it on a map. It matters where land is, and not just for the view.

It shocked me to learn how intimately rocks are connected to climate.  We didn't talk about rocks when we discussed global warming in school. We talked about rainforests and fossil fuels and atmospheric gasses. There was some vague talk about how volcanoes could impact climate, but nobody mentioned the Deccan Traps, so I thought it was all small-scale, temporary stuff. And nobody said diddly about actual rocks. They didn't talk about limestone and other carbonate rocks.  Nobody bothered to tell me just how much CO2 was stored up in those rocks, or said a word about how subducting carbonate rocks contribute to the CO2 outgassing from volcanoes. Boggles my mind, that does, and makes me look at the world in a whole new light.

And, cherry on top, plate tectonics shaped human evolution. Neat!

You know what I think surprises me the most about all this? It's how interconnected all this world is, what an intimate whole all of the different scientific disciplines make. We break them down into categories for convenience, and sometimes forget that you can't have geology without chemistry, physics, biology, hydrology... and you don't get climate without a heaping helping of geology thrown in. You can't understand one thing until you realize it's just a component of a much larger whole. Nothing exists in isolation. It all relates.

It didn't seem that way in school. Nobody ever taught it that way. So making these discoveries, seeing the way geology affects everything on earth, has been a tremendous surprise. More than that: a delight. It's delicious.

And I can't wait for the next surprise.


(A version of this post first appeared at En Tequila Es Verdad)