Friday Sprog Blogging: what's shaking?

Dr. Free-Ride: What have you been learning about in science this school year?

Younger offspring: Lots of stuff.

Dr. Free-Ride: Like what?

Younger offspring: We learned about rocks and minerals. Rocks are made out of minerals, and some rocks have more than one kind of mineral in them.

Dr. Free-Ride: So, what's a mineral?

Younger offspring: Umm ... I think quartz is a mineral. They can cut it in the shape of jewels. And also marble. But I think granite has more than one mineral in it. And we talked about how different rocks are formed.

Dr. Free-Ride: Oh?

Younger offspring: There are some rocks that form from the lava when volcanos erupt. We got to look at some pumice and see all the bubbles that were in the lava when it got hard to make the rock.

Dr. Free-Ride: I know another kind of rock mad by volcanos.

Younger offspring: What?

Dr. Free-Ride: It's called obsidian. It's really smooth and glassy, so I'm guessing that the lava that hardens to make obsidian has hardly any air bubbles at all.

Younger offspring: Yeah.

Dr. Free-Ride: So, do you know anything about earthquakes?

Younger offspring: I know that the really big ones can sometimes knock houses over.

Dr. Free-Ride: Uh huh. Do you know anything about why they happen?

Younger offspring: No. We haven't talked about that in science yet.

Dr. Free-Ride: That's OK. I'm pretty sure that in a couple years you will learn it in science. Do you have any guesses about what might cause earthquakes?

Younger offspring: Maybe a giant ... no, that wouldn't work. I don't think there are giant winds in outer space.

Dr. Free-Ride: That's OK. Strong winds can knock things over, so that's not an unreasonable guess. Any other guesses?

Younger offspring: Well, maybe a really big volcano eruption could be strong enough to shake the earth.

Dr. Free-Ride: That has potential.

Younger offspring: Hmmm ... or what if lots of magma bubbling up from the center of the earth made the land move up or down?

Dr. Free-Ride: Oh, like the way melting parts of ice shelves kind of make chunks of the ice crash down?

Younger offspring: Yeah.

Dr. Free-Ride: That's an interesting hypothesis.

Younger offspring: Do you know what causes earthquakes?

Dr. Free-Ride: I do. But you know, I'm actually really interested in what other causes seem like possibilities to someone who hasn't been told the official explanation that scientists have now. Before we knew, people had to start out with some good guesses. But once you know the explanation, it can be hard to come up with other guesses.

Younger offspring: I came up with some guesses.

Dr. Free-Ride: Yep, you're my pre-theoretic kid.

* * * * *

Dr. Free-Ride: So I know that you've been learning about earthquakes in school.

Elder offspring: Because of those assignments I had to do.

Dr. Free-Ride: Yes. And you know why earthquakes happen.

Elder offspring: Uh huh. The moving plates of the earth scrape against each other and create pressure and send out seismic waves.

Dr. Free-Ride: You know, don't you, that not so long before I was born a lot of geologists didn't believe that the continents were on plates that moved.

Elder offspring: Yeah, back in the 1930s or '40s.

Dr. Free-Ride: When exactly do you think I was born?

Elder offspring: Uhh ...

Dr. Free-Ride: I know you're learning math in school!

Elder offspring: The 1960s?

Dr. Free-Ride: Yes. If I'm remembering correctly, in the early 1960s there were still a lot of scientists who didn't believe in plate tectonics.

Elder offspring: I knew that.

Dr. Free-Ride: Did they teach that at school? I'm impressed.

Elder offspring: No, I read it in a book.

Dr. Free-Ride: Figures. Did the book say anything about what scientists thought might be causing earthquakes before they were on board with plate tectonics?

Elder offspring: I don't think so.

Dr. Free-Ride: Drat! I wish it had. That's the kind of question I find really interesting.

Elder offspring: Maybe they thought the earth shook because people had angered a god, or his dog.

Dr. Free-Ride: Hmm. That's an explanation, but not a very scientific explanation. Science tries to explain natural phenomena in terms of natural causes -- not supernatural ones.

Elder offspring: I know.

Dr. Free-Ride: So I'm betting that the scientists working in the 1930s and '40s were not trying to explain earthquakes in terms of angry canine deities. They must have said something about what they thought was causing earthquakes back then in their scientific papers.

Elder offspring: They published scientific papers back then?

Dr. Free-Ride: Yeah!

Elder offspring: I didn't think there were scientific papers published before, like, the 1970s. I thought before then people were too busy with politics.

Dr. Free-Ride: I wonder what gave you that idea. For at least a few hundred years scientists have been writing down their findings, sending them to other scientists, and reading what other scientists have written down about their findings.

Elder offspring: I didn't know.

Dr. Free-Ride: So, your science class in school is pretty ahistorical, isn't it?

Elder offspring: What?

Dr. Free-Ride: You talk about the facts we know now and the theories we have now to explain them, but you don't really talk about what scientists thought before we had those theories.

Elder offspring: No. Maybe they could teach it more be-historical?

Dr. Free-Ride: It's not "A-historical"! Ahistorical means "without the history". So they teach you about what we know, but not about how people figured out what we know. Sometimes, I think, the history can tell us something about good strategies for making more knowledge and figuring out the things we don't know yet.

Elder offspring: I think I'd enjoy learning about that. But I don't know that it will happen in science class.

Dr. Free-Ride: Well, keep reading those library books.

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You should really take them to Lassen NP. (Maybe when the road opens in June.) I guess that's less earthquake-y but there are lots of neat rocks. Some bubbling.

By Uncle Fishy (not verified) on 30 Jan 2009 #permalink

Well, maybe a really big volcano eruption could be strong enough to shake the earth.

Younger offspring is entirely correct about this.

I think that Tanya Atwater, who figured out the San Andreas Fault for her PhD, ought to write a book for kids about what it was like. (She broke new ground in many ways - going on research ships when women were supposed to be bad luck, taking new ideas from the ocean and using them to explain continental geologic mysteries for the first time ever.) She's recently retired from UCSB, and a great story-teller.

(I was born the same year that the term "plate tectonics" was coined, and although I've got a collection of old structural geology textbooks, I don't have any old seismology books. I know that earthquakes were understood enough to be used as a really important test of some aspects of plate tectonics, though.)

Sprog blogging is teh awesome! Younger one seems to be a budding geologist. Some of those guesses were pretty cool. Pre-theoretical kid would be a pretty cool name, like dr.bitchphd's pseudonymous kid.

There's an 1889 book, in French, online : Les tremblements de terre by Ferdinand André Fouqué ; it's sort of a summing-up of everything they knew at that point, which, from what I've read of the book, wasn't too much. They were still struggling to invent instruments that could accurately measure the force, timing, and direction of shocks. More of the data Fouqué offers is provisional or contradictory than is solidly established; there was a wealth of (quite varied) speculation about causes, and the influence of various earthly and astronomical factors, but speculation was all it was -- Fouqué sums it all up, though, pointing out weaknesses as he goes.