How do caves form?
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From Disney on March 21st, the musical movie of the year arrives in theaters. My name is Snow White. Flawless. Exquisite. Get tickets now. Waiting on you.

Snow White will have you on your feet. I think that's a wonderful idea. And cheering for more. I was thinking the same thing. Experience the magical story. Magic mirror on the wall. Who's the fairest one of all? Snow White. Disney's Snow White. Only in theaters March 21st. Rated PG. Parental guidance suggested. Tickets on sale now. From the brains behind Brains On, this is the moment of um. Answering those questions that make you go, uh-huh. Um, um, um.

Moment of Um comes to you from APM Studios. I'm Sam, the stalactite. I'm a stalactite. You know, one of those long, skinny, pointy things hanging from the top of a cave. I'm like a stone icicle. I've been hanging out in this cave for, oh, about 30,000 years or so.

A cave is a great place to grow up. Or in my case, grow down. We got bats, rats, and yoga mats. Seriously, someone comes in every other week and leads a yoga and meditation class. You've gotta try it. Plus, check out this echo.

Yeah, I wouldn't want to live anywhere else. But the other day, when I was following along with the humans meditating in the cave gallery, I did find myself thinking about the meaning of life, asking the big questions. There I was, spiraling into a void of simultaneous wonder and despair, as one does. And I was wondering, how did I get here? How did this cave even form?

Luckily, Sophie was wondering the same thing. How do caves form? So the question of how caves form is actually really difficult to answer because there's so many different kinds of caves. My name is Hazel Barton. I'm a professor of geology and I study caves.

So the cave that you probably think about is a cave that would be in limestone rock. So that would be rock that would look white when you look at it. And those caves form when rainwater lands on the ground and it picks up a little bit of carbon dioxide in the soil. And carbon dioxide is the same thing they use to make fizzy drinks. So when the drink is fizzy, it's got a bunch of carbon dioxide injected into it. And when you take the lid off, the carbon dioxide is released.

That carbon dioxide makes the water a little bit acidic and actually releases a gas and carves away at the rock. So over time, if you're adding a slightly acidic solution to this kind of rock, you carve a big hole in it and that would be a cave.

But over the years, we've studied caves in lots of different environments all over the world. And I think when I started, we thought there were about five different ways that caves form. And now we have 11 different ways that caves form. We've been able to show that bacteria can actually eat the rocks. These are rock-eating bacteria. So one of the really fun ways that we found caves form is in iron rock in Brazil.

And it turns out that there's, it's solid iron. So think about maybe a beam that holds a building up. You may have seen an I-beam, like a big structural beam in a building. And it's pretty hard and it's pretty solid. And in Brazil, they have big mountains made out of this. And in fact, the steel, the iron that we have in our buildings comes from Brazil.

And it was full of caves, thousands of caves, and they didn't know why. So we went down there and it turns out that the microorganisms get trapped behind the wall of the cave and they don't have anything to breathe. It's really hard for them to survive with no oxygen. So what they do is they start breathing iron. And when they breathe iron, they take it from being solid like a metal and they make it, they turn it into a soluble form. So it just dissolves in water and then the water leaves.

and when the water leaves, it takes the metal with it, and you end up with a hole, which is how caves form in iron. Um, uh,

Whoa, so this cave was probably formed by carbonated rainwater slowly eating away at rock over so many thousands of years. And it must have taken a long time for this cave to form, which is pretty special. Which means I am pretty special. Ah, existential dread gone. For now.

Anyway, pretty amazing stuff. And hey, did you know that the longest cave in the world is called Mammoth Cave? And it's in Kentucky. So far, scientists have explored 426 miles of it. If you wanted to cover that distance on a standard running track, you'd have to run around it almost 2,000 times. I think I'd rather stick to yoga. ♪

If you like this episode, take a second to subscribe to Moment of Um wherever you listen to podcasts. And if you want to visit a cave, check out the Brains On podcast where we have a whole episode recorded at Wind Cave National Park. Want to see our shows come to life? Head to YouTube where we've got awesome animated Brains On episodes. Search Brains On Universe on YouTube and subscribe.

If you have a question, existential or otherwise, we'd love to help you answer it. Drop us a line by going to brainson.org slash contact. See you next time and the next day and every weekday. Until then, time for my stretches. Stretch down towards the floor.

Feels good. Feels good in my quartz. Hey, friends. Molly, Sandin, and Mark here with some very big news. Drumroll, please. Drumroll.

We're hitting the road in search of adventure, fresh air, and you. That's right. We're going to be live at the Boulder Theater in Boulder, Colorado on Sunday, April 27th. Our science-themed live stage show takes the audience on an adventure through the brain, complete with magic tricks, dance moves, out-of-body experiences, mystery sounds, and a game show. Molly, you almost left out the most important part.

Yeah, Molly, don't forget the big party! Oh, right! After the shows, we're throwing a Braintastic Bash. Join us afterward for a VIP party where we'll play games, guess mystery sounds, pose for photos, and give as many high fives as humanly possible. Snag a spot by purchasing a VIP pass when you buy your show ticket. Oh, that reminds me. I've got to start training. These hands aren't going to high five by themselves. Five and five. Good idea.

And remember, spots are limited, so grab your tickets today at brainson.org slash events.