Welcome to Fossil Lake! The area I'm standing in right now is the largest and most complete representation of early Eocene life in the world, about 52 million years old. This area during the early Eocene is a lot like what modern Florida is today. You had crocodilians, you had paddlefish, all different kinds of turtles, shrimp, crustaceans, and we even had insects and bats, and a tiny three-toed horse that was only like two-and-a-half feet tall at the shoulder.

Not only do we have the actual animals preserved, but we have their behaviors. We have their feces, which are coprolites. We can tell what they were eating. We have leaves that have insects next to them, and you can see the little insect bites in the leaves. It's an amazing representation of the biodiversity, and there's nothing else like it in the world today.

So, we're on an expedition with the Field Museum, who has brought along a group of students to learn the trade and to help with the heavy lifting, and we're gonna go fishing for some 52 million-year-old fossils. Woo! 

Jim: Hi!
Emily: Hi. We've got our tools, now.
Jim: Yeah, these are your tools. This is your shim.
Emily: Shim?
Jim: This is one of the most important tools that we use out here. We use this for dividing up the limestone layers. Hold it.
Emily: So it's like a wedge.
Jim: It's like a wedge! Exactly.
Emily: It's got a sharpened end.
Jim: Yeah, one end's sharp and one end's used for hammering. And this is your other tool.
Emily: A hammer.
Jim: And that's all there is.
Emily: That seems pretty self-explanatory.

Emily: It seems to be, from my impression, that there's kind of a sweet spot in all the sediment. Like, you're not consistently finding animals all the way down like 500 feet. 
Jim: Right. It's a pretty thick member of rock, but there's a very, very, very thin layer where you have the most fossils. It's called the 18 inch layer. 
Emily: Is it because it's 18 inches?
Jim: Yeah.
(laughter)
Jim: Above and below the 18 inch layer are what's called oil capping layers, and this helps preserve the fossils in between those two layers. So, that's a sweet spot. That's what we're looking for. And once we hit the oil capping layer, we know that we're at the 18 inch layer, so we peel that away first and then we get to the fossil bearing beds underneath it. 
Emily: It's like taking a sandwich and picking it apart, essentially.
Jim: Yeah. Take off the bread, what do you have? Lettuce. Then you have tomatoes, then you have cucumbers. I don't know, I'm not a Subway or anything.
Emily: Well, that's pretty cool. And then you can see, like, stuff that's on the bottom of this 18 inch layer, which doesn't seem like significant enough. You know, it doesn't seem like that would cover thousands of years of time. 
Jim: It's amazing. Yeah, it's pretty compact, fairly compact limestone. Uh, but this 18 inch layer only represents several hundred or several thousand years of this lake system's 15-million-year life span. 
Emily: That's crazy.
Jim: This was a very long-lived lake system. And this is only a tiny slice of that ecosystem.
Emily: Because the conditions typically aren't ideal for fossilization.
Jim: Typically aren't ideal for fossilization, yeah. This time period, the conditions were ideal, so everything and anything that fell into this lake and sank to the bottom, got buried, was fossilized.
Emily: Wow. 
Jim: Everything from microscopic bacteria all the way to mammals and birds, reptiles. 
Emily: That's crazy. So we don't even know what we're going to find here today.
Jim: We don't know. Typically we find fish, but every so often we get surprised by something else. That's what keeps us coming out here year after year, are for these unusual, rare fossils that you don't find every day.
Emily: Yeah.
Jim: But it's still fun finding a fish.
Emily: Yeah!
Jim: It's like a fishing trip.
Emily: It's like a 52-million-year-old fish.
Jim: Unbelievable. So, shall we get in our boat and go fishing?
Emily: Yeah, let's go fishing. 
Jim: Ready?
Emily: Yeah.
Jim: Canoe.
Emily: Here we go. Woo! Woo! Woo! (laughter)

Jim: So if you want to tap away some of that, then the trick is to tap and pull back. Tap and pull back. Nice rhythm going. Oh, look, we found a fish already.
Emily: Really?
Jim: Yeah.
Emily: Where? Oh there it is!
Jim: You see? 
Emily: Yeah!
Jim: It's a Cockerellites.
Emily: How can you tell so quickly?
Jim: Okay, we call these things football fishes because their bodies are shaped like footballs. 
Emily: Well, that would kind of make sense. 
Jim: I know. Not a soccer ball, though. American football.
Emily: American football, okay.
Jim: So there is a backbone, and there is a football shape right there.
Emily: Gotcha.
Jim: And the tail is somewhere here. So, the skull is still underneath that rock.
Emily: Oh, okay.
Jim: All right, you have your shim ready?
Emily: Yup, I do.
Jim: You have your hammer ready?
Emily: Yup.
Jim: You have a name for your shim? 
Emily: No.
Jim: You should name your shim.
Emily: It's Jim the Shim.
Jim: Jim? Oh--gah--no.
Emily: (laughter)
Jim: So, we have a crack started on this side already.
Emily: Yeah.
Jim: And I'm gonna start to get it a little bit thicker and you can put your shim next to it.
Emily: Okay.
Jim: You see how one side's flat?
Emily: Yeah.
Jim: And one side's beveled?
Emily: Yup.
Jim: Always have the flat side down because that'll help push the slab up.
Emily: Oh, okay. Wow.
Jim: So there's the crack, and you're gonna put yours in right about there.
Emily: There?
Jim: So hold it with one hand, hammer with the other hand.
Emily: Like there?
Jim: Just like that. Nice and flat. And next thing you do, we go to the larger tools. This is basically a shovel that has a sharpened end on it. So, it's a giant shim.
Emily: I see.
Jim: And we're gonna use two shovels.
Emily: Okay.
Jim: This will help separate it now, even more.
Emily: All right.
Jim: Now we're gonna slide the shovels into the crack that we made, so take your shovel.
Emily: Got it. Like, right in here?
Jim: Right in there. Ready? Count it up: up, down.
Emily: Up, down, up, down, up, down, up, down, up--
Jim: Okay, now stop. Put your shovel in deeper. Okay, count it up.
Emily: Okay. Up, down, up, down, up--
Jim: Now you see the crack at the end?
Emily: Yeah.
Jim: We've broken free, so now we can actually lift it up--
Emily: Wow.
Jim: --and see if there's any fossils in there.
Emily: Oh, nice! Okay. So take this?
Jim: So, you do it by yourself. I'm gonna be on the other side--
Emily: What? Okay.
Jim: --and we're going to lift it up and point it to the sun so we can see the fossils.
Emily: All right.
Jim: So, lift.
Emily: Well, there's some trace thing.
Jim: Mm-hmm.
Emily: What is that?
Jim: That's a branch, actually. 
Emily: Oh, all right.
Jim: So we have plant matter in here. That's a part and counter-part of that.

Jim: All right, so we just removed the plate and cleaned up around it. So we have a nice, fresh surface here, and now we're gonna move to the left. The whole goal of all this is to remove all the rock from around this plate. And you see these mystery feet here?
Emily: (laughter) Yes, it's hard to ignore the mystery feet.
Jim: Those are very important mystery feet. So, as we're removing material around this plate that contains fish, if we remove a layer that's underneath that plate, it'll pull the plate up and break the fish.
Emily: Oh, okay.
Jim: So he's there to hold it down.
Emily: All right.
Jim: So keep your foot down. 
Emily: Yeah, don't move.
Jim: Good. So, there's one last piece to get around this fish. Go parallel with the crack.
Emily: So, here? Or this way. 
Jim: These cracks. 
Emily: These cracks!
Jim: Yeah. Just like that. 
Emily: Okay.
Jim: So now, tapping in. 
Emily: Woah. All right.
Jim: (laughter) Wow, that was easy. 
Emily: Well, and then I just lift it up?
Jim: Just lift it up.
Emily: That was uncommonly easy. 
Jim: That was uncommonly easy.

Jim: So we worked all the rock away from around this plate, so your job now is to go underneath the plate to remove the fossils. 
Emily: And just right here?
Jim: Right there for now, but you're always watching for a crack. Hit it one more time. Oh, you're there.
Emily: That?
Jim: You see how it's moving? The whole thing is moving.
Emily: Yeah.
Jim: It's free.
Emily: It's free?
Jim: It's free.
Emily: It's already done?
Jim: So all you need to do is grab one end at a time and just lift it up.
Emily: Let's see. Oh man, pressure's on. 
Jim: Pressure is on. 
Emily: And, here. That's it.
Jim: Hold it up to the sunlight so we can see them really well.
Emily: Oh you can see them, yeah.
Jim: Mm-Hmm.
Emily: There's one here, and there's one right here. There they are. What kind of fish are they?
Jim: Those are both Knightia, so those are the most common types of fish that we find out here. And so now we're gonna put it into the Field Museum pile and take it back for our collection.
Emily: Cool! We did it, there you go. Fishes.

Emily: Put it on the pile with all the other fishes. Set it right there. Yeah.