Friday Sprog Blogging: fossils.

Dr. Free-Ride: What have you been learning in science?

Younger offspring: I've been learning how to make fossils, and imprints.

Dr. Free-Ride: Tell me how.

Younger offspring: Well, we got some salt dough --

Dr. Free-Ride: What's in salt dough?

Younger offspring: Flour, water, and salt.

Dr. Free-Ride: OK

Younger offspring: And we made it into thick circles.

Dr. Free-Ride: And?

Younger offspring: And then we got either a shell, a leaf, a stick, or this seed cone, or conifer needles, and we pressed it down in the salt dough.

Dr. Free-Ride: And then what happened?

Younger offspring: And then it had to dry out.

Dr. Free-Ride: So, it sort of left an impression on the salt dough circle?

Younger offspring: Yeah. But mine cracked.

Dr. Free-Ride: That's OK.

Younger offspring: Because my partner pressed the magnifying glass in my salt dough!

Dr. Free-Ride: That's kind of uncool. You should have a talk with her about --

Younger offspring: She wasn't here today.

Dr. Free-Ride: So, is this how fossils got made in the time of dinosaurs?

Younger offspring: No.

Dr. Free-Ride: How did the dinosaur fossils that we have today get made? Did you talk about that?

Younger offspring: Well, dinosaur fossils -- wait, are you talking about dinosaur prints?

Dr. Free-Ride: Sure.

Younger offspring: Well, the prints. Dinosaurs were walking in, like, the rock, and then the rock got hard, once they passed away, and then it cracked up into pieces, and there was one piece with a dinosaur footprint on it. Then it got fossilized because it went back deep into the dirt and stayed there for a long time. And then the extra rock on top of it and dirt on top of it washed away, so it was found on the surface. And then they took it to investigate it.

Dr. Free-Ride: I see. So, something about where the dinosaur put a foot down not only took an impression of the footprint, but it also got hard permanently?

Younger offspring: Yeah.

Dr. Free-Ride: OK, so it wasn't just mud or sand or something, it was mud or sand or something under very special conditions where it sort of got stuck that way.

Younger offspring: It got fossilized.

Dr. Free-Ride: You know when I say, don't make that funny face in the mirror, it might stick that way? Is there a chance that your face might fossilize that way?

Younger offspring: No.

Dr. Free-Ride: What if you were looking at your reflection in a tar pit? Is there more chance that your face might fossilize that way if you fell into the tar pit making a funny face?

Younger offspring: Yes.

Dr. Free-Ride: Is this why you're very careful about not making funny faces while looking at your reflection in a tar pit?

Younger offspring: I don't go to a tar pit!

Dr. Free-Ride: Maybe next time we're in LA we can go back to the La Brea Tar Pits.

Younger offspring: You want me to fall in?!

Dr. Free-Ride: No, but I think you might enjoy looking at the fossilized stuff --

Younger offspring: Mammoths? I like mammoths! They're cool. They have tusks, but no big ears.

Dr. Free-Ride: What have you got against big ears? You've got relatives with big ears.

Younger offspring: Who?

Dr. Free-Ride: So ... I have another question. We don't just have footprints left from dinosaurs --

Younger offspring: Oh, the dinosaur bones! They, like, die, and then their skin parts rot away, and they go under the dirt, and the dirt covers it, and then after many many years, the dirt gets washed away and the bones are found a little deeper. But the first and second, and maybe third, layer of dirt, it gets washed away, and the fossils are found underground, and they can tell how old they are by how deep they are.

Dr. Free-Ride: I think if I remember correctly -- and maybe they've changed it since I learned it -- that's called "stratigraphy".

Younger offspring: I don't know.

Dr. Free-Ride: They're not using the fancy terms, then. That's fine. So, they're not like normal bones when they dig them out, right?

Younger offspring: No, they are not.

Dr. Free-Ride: They're fossilized bones. So there must be some sort of process going on to sort of replace the normal bone material with material that's more like rock.

Younger offspring: I know what a coprolite is!

Dr. Free-Ride: What are -- oh, I know what coprolites are.

Younger offspring: Dinosaur poop that's fossilized! I learned that on something from PBS Kids, even though I'm 8.

Dr. Free-Ride: That's fine. You can still learn stuff that's meant for younger people. I learn stuff that's meant for you all the time. Do you think at some point you'll learn more about the process that changes the dinosaur bones from being like bones to being like rocks?

Younger offspring: I'll give an example of that. I'm a dinosaur and this cardboard tube is my bone. RAWR! RAWR! RAWR! And then, later on, I die.

Dr. Free-Ride: Yes, as one does.

Younger offspring: My skin rots away. My bones are left. And then, dirt covers it, more dirt covers it, and even more dirt covers it. Dirt and rock. And then --

Dr. Free-Ride: Wait, what do you know about layers and layers and layers of dirt? If you were underneath all that, what would you notice right away?

Younger offspring: Mmmm.

Dr. Free-Ride: What if you were under four blankets? What would you notice?

Younger offspring: That I was getting hot.

Dr. Free-Ride: Well, OK, and also that the four blankets would end up being heavy. If you had layers and layers and layers of dirt, I bet they would be heavy, too.

Younger offspring: And they would cover it, and kind of stick to it, and then for many years -- pretend this is many years --

Dr. Free-Ride: (quietly) It feels like it.

Younger offspring: -- and the dirt covers it, and the dirt gets washed away. WOOOSH! But they're still buried like one, two, or three layers -- it depends on how old they are. And then scientists -- paleontologists -- dig the dirt and find it's a fossilized dinosaur bone.

Dr. Free-Ride: And then they have to figure out what kind of animal it come from.

Younger offspring: Which is a dinosaur.

Dr. Free-Ride: Well, sure. But there's lots of different --

Younger offspring: (looking closely at the cardboard tube) Wait, it's a mammoth! This is a mammoth's tusk!

Clearly, a deeper explanation of the mechanisms of fossilization will have to wait for another day.