Particles of Thought

Hakeem: So what separates the fossilized plants from ... I imagine everything doesn't get fossilized.

Kirk: Yeah.

Hakeem: Yeah.

Kirk: So here's the key thing that you have to know about fossils is that in order to become a fossil, you've got to die and you got to get buried. And if you don't get buried, say you just fall over in the forest somewhere, you're going to rot away. So it's death plus burial. So if you're a dinosaur, you fall over and you die, chances are you're not going to become a fossil, unless you live in a place where stuff gets buried. And what are those places?

They're places like Louisiana, for instance, right? Louisiana, the whole landscape is sinking slowly, and the stream is always dumping out sediment and putting more layers on it. So in an area that's sinking is what I call D World, or deposition world. And if you were to drill a hole beneath New Orleans, you would go down almost 20,000 feet in layered mud that's only 25 million years old.

Hakeem: What?

Kirk: That's literally miles of thickness.

Hakeem: Yes.

Kirk: Miles. So if a fish died in New Orleans 10 million years ago, it would be 10,000 feet down. And in the sediment it was buried, and it was being compacted into rock.

Hakeem: So I've seen this image geologically of the Gulf of Mexico, and how it goes out underwater, then there's this big giant cliff. So all of that stuff is from the river?

Kirk: Yeah.

Hakeem: Whoa.

Kirk: And from rivers dating back to millions of years. So the earth is, as it erodes mountain ranges, all the sediment, ground up mountain ranges end up at the edge of the continents, and piling up in thick layers of sediment or limestone or other kinds of stuff. And that's where you create the fossils. An animal dies, or animal, plant dies, is buried in an area that's sinking, which buries it deeply, and that turns the sediment into rock, and they're at depth.

And then eventually what happens is, some other first phenomenon pushes that area back up. So areas that were depositional areas, or D-World become lifted up into what is called E-world or erosion world.

Hakeem: Erosion.

Kirk: So if you can look at North America, for instance, most of North America right now is erosion world, or E-world.

Hakeem: It's getting eroded away.

Kirk: There's mountains. Anytime you see a hill or a mountain, you know that stuff's eroding away. Look at the Mississippi River drainage.

Hakeem: Any time you see a river, right?

Kirk: Yeah. Exactly. In some areas ... and so there are ... think about this, there are rivers in erosion world, like the Colorado River is cutting the Grand Canyon, not a good place to become a fossil, that's just grinding away and taking it out to the sea.

Hakeem: And it goes side to side and meanders.

Kirk: But that same river, Mississippi, when it gets down to New Orleans, great place to make a fossil. So that's the E-World D-World difference. And the best place to find fossils, and maybe the best place in the world to find fossils, is Western United States, because most of the last 500 million years that landscape was sinking. It was D-World. But then when the uplift of the Rocky Mountains started, it pushed that area back up, and exposed those rocks in E-World. So you want D-World-

Hakeem: So you bury them-

Kirk: Bury them.

Hakeem: Then lift them, and erode the stuff off the top of them, and now they're exposed.

Kirk: Exactly. And sometimes you uplift them in an irregular way. So in one place you might be able to see a cross section of the entire stack. And there's a place near Cody, Wyoming where you can see from 2.5 billion years to 60 million years in one spot.

Hakeem: Geez.

Kirk: It's better than the Grand Canyon.

Hakeem: That is ... and so, because they've been lifted and turned, now it's more horizontal, or at an angle rather than-

Kirk: Yeah, exactly. It used to be flat, and they turned up and they're almost vertical, and you just count the pages like this, all the way through.

Hakeem: Wow. And each layer has its representative fossils.

Kirk: Exactly. Always, there's sort of local D-World, like the immediate area around you. You're standing next to a mud bluff and it slumps down and buries you, you just got buried in a little narrow piece of D-World.

Hakeem: I see.

Kirk: But if you wanted to look at it at the continental scale, most of North America is E-World, but they're little local ponds and little local lakes. But those local things are not going to get preserved. They'll eventually fill up and erode away too. So the fossils are going to be in this places where the whole landscape is sinking.

Hakeem: Whole landscape. So what places would that be on earth today?

Kirk: The edges of the continents primarily, or the shallow, low elevation parts of the margins of the continents.

Hakeem: Okay. And is that generally true throughout history?

Kirk: Yeah. As a result, we really don't have much of a fossil record for mountains or hills.

Hakeem: Wow. So for example, right now, humans are distributed primarily along coastlines. So would it be the case that land animals, even though it is geographically limited, it's still a good representation, because that's where most life is going to concentrate anyway. Is that fair?

Kirk: It's true. That's probably the case. But you're still going to miss the mountain goats and stuff like that.

Hakeem: They still exist.

Kirk: It's things that live only at high elevations, or even on the Great Plains. Some of those things do get preserved. The animals of the Great Plains are preserved because the Rocky Mountains came up, and all of a sediment coming off the Rocky Mountains shed and buried things under river sediments. And then that area's still coming up, so those river sediments are now being exposed. And so you have kind of local D-World is a source of good fossils on continents. And we found an amazing site in Colorado in 2012, that was a lake on top of a hill at 9,000 feet.

Hakeem: Whoa.

Kirk: And it filled up with-

Hakeem: Lake Tahoe.

Kirk: ... No, it was at Snowmass Ski Area.

Hakeem: Oh, Snowmass.

Kirk: It's right .. 700 yards from the base of ski area there's a little 12 acre lake that turned out to have been an ice age lake, that filled up between 120,000 years ago and 50,000 years ago. And we found 50 mastodons and 12 mammoths in this one little lake, in 70 days of digging. It was an amazing thing. But that was a little tiny lake on top of a hill that was a little temporary bit of D-World.

Hakeem: Yeah.

Kirk: And in the future that'll erode away and go away. But we got it before it eroded away.

Hakeem: Wow.

Kirk: Just our timing was very good.

Hakeem: Good timing. But over geological history, a lot of those have coming on.

Kirk: Yeah. Oh yeah. Because that's the top of the hill, it's going to go, right.

Hakeem: It's going to go.

Kirk: Hills go away. Mountains go away.

Hakeem: They're temporary.

Kirk: Yeah. Never trust mountain ranges, they're undependable. They'll erode away.

Hakeem: All right, all right. You can't depend on them. All right.

Understanding Fossil Types and Preservation

Hakeem: Well, let me ask you this other question, then. The fossilization process. So I've been to the Painted Desert in Arizona with all the fossilized trees, and they're rock. So pretty much fossil equals not organic stuff in its current composition. It's minerals, right? Is that always the case, or do you actually get some organic bits here and there?

Kirk: So I would define fossils different. What you've described is a petrified fossil where the fossil has been turned into rock. That's one type of fossil. A fossil is basically anything old. It's a very-

Hakeem: Okay. It's broad.

Kirk: It's very broad, because we have fossils that are almost unaltered entirely. I can show you, for instance, a site that we worked up in the Canadian Arctic Islands that was 5 million years old, and the wood looked like driftwood off a beach.

Hakeem: So it's still wood?

Kirk: It's just wood. It just happens to be 5 million years old.

Hakeem: Wow.

Kirk: I have a site in North Dakota that I dig called Ginkgo Salad, and the reason we call it Ginkgo Salad is when you crack the rock open, this is 67-million-year-old rock, the ginkgo leaf peels off the rock. It's a leaf.

Hakeem: Wow.

Kirk: You can eat it.

Hakeem: It's like the pressed leaf in your...

Kirk: It is.

Hakeem: But it's encased in rock?

Kirk: Yeah.

Hakeem: Wow.

Kirk: Petrified wood is wood that's been invaded by silica-rich water. So it turns the wood, or the wood is replaced with glass, effectively. But that also happens...

Replaced with glass effectively, but that also happens. I have places where fence posts are petrified because of the groundwater, if it has silica or calcium carbonate in it. And you can actually take a chunk of petrified wood in some cases and put it in hydrofluoric acid, which is an acid that dissolves silica. It dissolves glass. So don't put hydrofluoric acid in a glass jar because it'll dissolve.

Hakeem: Wait, HF?

Kirk: Yeah, HF.

Hakeem: Oh man.

Kirk: Nasty stuff.

Hakeem: Nasty stuff. I used to work in the semiconductor-

Kirk: There you go.

Hakeem: ... field and then we had to watch these horrible videos of HF accidents.

Kirk: It kills people.

Hakeem: Yeah.

Kirk: So, you take a piece of petrified wood and you put it in hydrofluoric acid, it will dissolve the silica out and give you the wood back.

Hakeem: Wow.

Kirk: The wood structure is still there.

Hakeem: So we're talking tens of millions of years old.

Kirk: Could be less. I mean,-

Hakeem: I'm saying up to, right? Could that work with something-

Kirk: Oh yeah. Oh yeah. I mean, there are plenty of fossils from 400 million years old where you can dissolve away the rock and get the organic material. Like the coal seams of West Virginia? There are these things called coal balls, which are concretions made up of calcium carbonate that formed around these plant parts.

What you do is you saw them in half, you dip the flat surface in a light acid, which etches away the calcium carbonate, and then you lay a little bit of acetone on there, you put a sheet of acetate and peel off, and you can get a peel of the cell structure of the plant.

Hakeem: Wow, and look at it under a microscope-

Kirk: Yeah, cell by cell. And that's 400 year old plant.

Hakeem: 400 million?

Kirk: 400 million. Sorry.

Hakeem: Wow.

Kirk: 400 million. So now you're starting to get the joy of paleobotany, right?

Finding Fossils: The Secrets of the Crack

Hakeem: Yeah. This is dope, man. This is dope. So you said something, and this is something I've always wondered. I see these videos, they're walking in a stream, or they're out in some place where there's all these big rocks and they're like, "Ha." And they grab a rock, hit it with a hammer, and open it up, and there's a fossil right there.

I'm like, "How do you know?" How do you know that that rock had a fossil in it? And then what is the rate? You've been doing this a long time, you're probably good at it. Is it one out of 10? How does this work, man? We want the secret. I want to find fossils in my backyard.

Kirk: Perfect. There's several secrets here. One is you don't find anything unless you look for it. So that's a pretty obvious thing. And so certain kinds of fossils are in the rock, and fossil leaves are in the rock. And if the rock erodes away, it just erodes with the fossil.

Because if you think about it, here's how a fossil leaf gets formed. Leaf is on a tree. Leaf falls off the tree into the stream. Leaf gets buried by sand at the bottom of the stream. It's in a D world situation so the stream gets buried by more streams.

After a while, that layer is so deep, it becomes a hard sedimentary rock. Then later on, that area is uplifted. Now that rock's exposed to the surface. That leaf is in the rock. So I go walking along with my pickaxe, and I'm digging holes and digging holes. I'll split a chunk of rock and crack it open, and I do this when I'm hunting for fossils.

I might do that 100, 1,000 times a day. Just look, crack a rock. Nothing. Nothing. Nothing.

Hakeem: But you have some sort of criteria to determine which rock you're going to crack open, right?

Kirk: I do, but sometimes when I have young interns, I say, "Just go dig holes." Because sometimes my criteria locks me into missing things.

Hakeem: I see.

Kirk: Right? I think I know where things are,-

Hakeem: Right.

Kirk: ... I think I do but I don't know what I don't know as always. And so I sometimes have the uneducated people digging holes too. And sometimes they find amazing sites by random, and I'm like, "Oh, I could find fossils there too."

But say you find, you crack the rock open and remember there was a leaf that was there, but the leaf is usually rotted away leaving a leaf-shaped hole in the rock, which means when you hit the rock with a hammer, it wants to open up there because a plane of weakness.

Hakeem: Oh.

Kirk: So it's predisposed to open up where the fossil is.

Hakeem: I see.

Kirk: So when you crack a rock and there's a leaf or even a fragment of a leaf, you're like, "Ah, okay." Now remember this, leaves are like potato chips. You don't just get one.

Hakeem: Oh.

Kirk: Right? It came off a tree. A typical tree has hundreds of thousands of leaves.

Hakeem: Really?

Kirk: And I know this because I once cut down a tree and counted the leaves.

Hakeem: Man, you are committed to the art.

Kirk: I wanted to know.

Hakeem: You are,-

Kirk: I wanted to know.

Hakeem: ... I love that. Hey, you know what? I believe it now because you know what I did? I have a bunch of trees. I'm in a country place and so I bought one of these extendo automatic cut the limbs off because they're growing into the areas they shouldn't. And man, when it came time to get all that stuff and put it in bags, I was thinking, "There got to be 100,000 leaves on this tree." Not a bad guess.

Kirk: I had this thought. I said, I want to do this because I really just want to know. And I selected a 50 foot tall red maple tree that was about this big around at the base, and I sawed it down with a buddy of mine, and then we cut off all the branches and stacked them all up.

And then we sat down and we had a counting system where we had a pile of sticks and every time you counted 100 leaves, you put a stick in the pile so you wouldn't lose count. And we took 18 hours and we counted leaves for 18 hours, and this tree had 99,284 leaves on it. So your 100,000 leaf was a good guess.

Hakeem: Well, I just say that because you already said it, but you, I planted that. You planted that, right? You led the witness. It reminds me of that thing where they show up with the jelly beans. They're like, "Guess how many jelly beans are in the jar?" So you did that for a tree and you got the-

Kirk: Exactly.

Hakeem: ... number.

Kirk: So that was just one tree, but it was the average tree in this forest. I measured all the trees in the forest. I said, "I'm going to hit the average tree."

Hakeem: Well, let me tell you, a physicist would never do it that way. There's two ways we would do it.

Kirk: Okay.

Hakeem: One way, either we would chop off all the trees, chop off all the leaves, put them in a big pile and weigh it, and then weigh one leaf. Now, think about it. The other way is we'll say like, "Oh, let me take a meter by meter by meter volume, count the number of leaves in there, and then estimate the volume of the entire canopy."

Kirk: Well, you know what I had done actually before then, because leaves all, in the Northeast, all the leaves fall off in the fall.

Hakeem: Okay.

Kirk: They all fall off in the fall. So I had gone to that same forest where there was leaf litter in November, so all the leaves are off the tree. And I had measured one meter square and counted the leaves in one meter square, and I divided that by the number of trees in the area, and I'd come up with an estimate of 103,000 leaves.

Hakeem: So, close, see?

Kirk: So there's more than one ways to skin a cat or count leaves on a tree.

Hakeem: Right, yeah.

Kirk: So now whenever I look at a tree, I'm like, "That's a one million leaf tree, or there's a 600,000 leaf tree. There's a 100,000 leaf tree." But my point is, when you're looking for fossils-

Hakeem: You have intuition about it now.

Kirk: Well, yeah. I mean, it's a useless intuition. Who cares about how many leaves are on a tree?

Hakeem: You don't know, man, that might save your life someday. You're out in the... If only we had a tree with 200,000 leaves. There it is. There it is.

Kirk: So, but get back to the fossil now-

Hakeem: Gilligan wish he could have known that.

Kirk: Remember the professor?

Hakeem: Yeah. The professor, of course.

Kirk: So, when you're digging fossil leaves, it's rare that a leaf is going to be there by itself because it came off a tree that had 100,000 leaves. So if you find one leaf, you're going to find more. So when I find a single leaf, then I stop. I get the other tools out, and I dig a hole. And almost always when I find one leaf, I can find hundreds of leaves.