Particles of Thought

Kirk: And if you go to Miami, all of Southern Florida is sitting on top of fossil coral reefs.

Hakeem: Oh wow.

Kirk: The whole state of Florida has got coral reef fossils underneath it. Anywhere you go, you dig a hole-

Hakeem: Except the sinkholes.

Kirk: Well, the sinkholes are holes in the coral reefs.

Hakeem: Why would that exist?

Kirk: I was just in Florida three months ago, and I had the best sinkhole experience.

Hakeem: That may be the first time that sentence has ever been uttered on planet earth, because sinkhole experiences are typically tragic.

Kirk: Yeah. Well, I want to... Now we're going to talk about sinkholes in Florida, all right?

Hakeem: Oh man.

Kirk: So, the bedrock of most of Florida is limestone that's about 35 million years old.

Hakeem: Wow.

Kirk: So it was deposited at the bottom of the sea, and there's a thick layer of limestone. And whenever-

Hakeem: What forms limestone?

Kirk: Limestone are fossil reefs.

Hakeem: Oh.

Kirk: Okay? It can be lots of different things, but in Florida, they're fossil reefs. They're coral heads and just what you're talking about.

Hakeem: Right. Why is the word lime in there?

Kirk: Because it's calcium carbonate. And when you bake calcium carbonate, you get lime, which is used to make concrete, right?

Hakeem: Oh.

Kirk: And so it's lime is an old English word for this-

Hakeem: Calcium carbonate.

Kirk: ... calcium, right? And so limestone is calcium carbonate. And so it forms in ocean situations. It can also form in freshwater, it turns out. But in ocean situations, organisms build these reefs, or just layers of microorganisms that make limestone. Like the cliffs of Dover, for instance, are a non-reef version of the reefs.

But Florida are these reef ones, and you can go to outcrops anywhere in Florida and you'll see the coral sticking right out of the rock. I mean, it's, there it is. It just takes zero-

Hakeem: 35 million year old.

Kirk: Yeah. It takes zero imagination to see it. You're looking at the reef and-

Hakeem: Man, I used to live in Florida and I don't ever remember seeing that.

Kirk: You don't look at the ground enough, man. You're looking at the stars too much.

Hakeem: Yeah, I'm looking up.

Kirk: So, I went to Florida because I'm working on this fossil atlas in the United States, and I had heard that Florida had great fossils. And I went to the University of Florida Gainesville, where they have a great museum. And I went out to a limestone quarry where they're quarrying limestone to make concrete and all this stuff.

And we first stopped at piles from the ground up limestone, and I was looking around, I found a beautiful fossil crab. A fossil stone crab that was that big.

Hakeem: Wow.

Kirk: And lots of chunks of snails and clams, all the kind of things you'd see living around a reef. But then, here's the kicker. That reef was 34 million years ago. Over time, the earth goes up and down, depending on different things. Where the continents are.

Hakeem: You mean the surface goes up and down?

Kirk: The surface goes up and down, and the sea level's also going up and down. So if you live near the coast, either the sea level can go up and flood the land, or the land can go up and drain the sea, or both happen over time quite a bit. So, the limestone of the 34 million year old limestone from Florida, which used to be under the sea, is now above the sea. It's maybe 30 or 40 or 100 feet above the sea.

Limestone is dissolved by rain water, right? Because the rain water's got a little bit of dissolved carbon dioxide in it, which makes it carbonic acid. So when a raindrop's got carbonic acid, it hits the limestone and it dissolves a little bit. So limestone forms caves. That's where you find all the big caves like Mammoth Cave in Kentucky, know Carlesbad Cavern in New Mexico.

Hakeem: Wait a minute, wait a minute. So, Mammoth Cave is an old reef?

Kirk: Yes. In Kentucky.

Hakeem: Dude.

Kirk: Yes. Yes. Now you're getting it. You're with me on this one. So you have this landscape now that the rain is making holes, and these caves can get huge. You've seen Mammoth Cave.

Hakeem: Oh yeah. I've been in a few caves. I haven't been in Mammoth.

Kirk: All of those caves are formed by uplifted ancient-

Hakeem: Oh my God,-

Kirk: ... limestone.

Hakeem: ... now that you mention it, I was in this island in the South Pacific. The Cook Islands. And it's an ancient, it's a coral island.

Kirk: Yeah, of course.

Hakeem: And it's full of caves.

Kirk: Exactly. Right? So, think about marine limestone that's been uplifted. Think about the best analogy back to food is Swiss cheese.

Hakeem: Swiss cheese.

Kirk: It's a block of cheese with holes in it all over it, right? So now, what a sinkhole is, is when you put some weight on the top of a part of the sinkhole, because when you lift it up, limestone has formed these holes in there, they often fill up with groundwater. So it's like a Swiss cheese that's full of liquid.

Hakeem: And that gives a support as well?

Kirk: So the top of the sinkhole is there, and you park your car on it, and your car weighs enough to crack the hole, and suddenly the whole thing collapses in on itself and you have a round lake.

Hakeem: And that's the thing is they're circular.

Kirk: Yeah, because they're round holes and they become around lakes. So now you have this thing that's there, and it's a lake that's got steep walls on it because you collapsed in the side. And if you're a turtle or an alligator, you find your way in there and they fill up with turtles and alligators, who are living happily in there.

If you're an animal walking by and you go for a drink in the water or you fall in, you can't get out because of the steeper walls so they become a trap. Now over time, dust and stuff fills it up and the sinkhole fills up with mud and bodies of all the animals that got buried there.

Northern Florida has got, we went to this one limestone quarry, and you could see where they're cutting the wall you could see cross-sections of in-filled sinkholes full of fossil mastodons and rhinoceroses and giant ground sloths and manatees-

Hakeem: Whoa.

Kirk: ... and alligators and turtles. And so I'm like, "This is the coolest thing I've ever seen."

Hakeem: Right. So it's a big cylinder.

Kirk: It's a cylinder full of skeletons.

Hakeem: Jeez.

Kirk: And the museum is chockablock full of skeletons, all of them younger than the age of the limestone, 34 million years, all the way up to the Ice age 2 million years ago.

Hakeem: Wow.

Kirk: And we went digging. We went to this other place called Montbrook, and they give you a little knife to dig with. And I dug myself on first I found a beautiful fossil turtle with a skull intact. And then I found-

Hakeem: So do you get to keep this stuff or-

Kirk: No, it goes to the museum there.

Hakeem: Oh, okay.

Kirk: Whenever I go, my wife's like, "It's some museum I'm working for," usually my museum, but I'm always like, "This cool fossil."

Hakeem: But how does that work? Is there a regulation around that?

Kirk: Sure. If you own the property, you own the fossils.

Hakeem: Got it.

Kirk: Which means that if you, I mean, which is a good argument to buy property. Own a lot of fossils, right? But this is a piece of property that's owned by a private citizen who is letting the University of Florida dig there. They've been digging for 10 years.

They have, from this one little top of a little sinkhole extracted something like, I don't know, 100 different rhinoceroses.

Hakeem: God, that's nuts.

Kirk: And when I was there, I dug onto a rhinoceros.

Hakeem: Wow. Wow. That's amazing.

Kirk: So I tell you, I left Florida a changed person. Because I had been going down to Florida a lot, looking at fossils and things, but I didn't really realize the Swiss cheese thing. And there are thousands of those sinkholes, and they're all full of amazing fossils.

And as a result, Florida has one of the best fossil records of early mammals in the country.

Hakeem: Wow, jeez.

Kirk: If you want a fossil mammal between the age of 34 million and now, Florida and Nebraska are your two top places.