14 January 2008

Hot, gooey fillings

Posted by Jessica Ball

My least favorite geological misconception would have to be one that I come across a lot as an aspiring volcanologist: The Earth’s mantle is a molten sea of liquid, and the crust “floats” on it.

Now, I suppose this is a perfectly good way to provide a simple explanation to young children who are too young to understand the rheology of rock in the mantle, or the fact that it can flow and not be a liquid. (I certainly believed it when I was little. Mind you, this was pre-elementary school and all I had to go on was “The Magic School Bus Inside The Earth.”)

But things are not so simple! (Insert totally fake tone of wonder and awe here.) While it would be a whole lot easier to call the crust solid and the mantle molten and leave it at that, it isn’t accurate. Better to divide the Earth up by the way things actually are (and behave) – using the lithosphere and asthenosphere (or aesthenosphere, which I prefer but my spell-checker doesn’t) and their associated subdivisions. The asthenosphere being, of course, the fun part, where rock actually deforms plastically – in short, flows – and where only a few percent of the material is actually molten.

Gasp! You mean what my kindergarten teacher taught me (and what a lot of people I come across seem to believe) is a lie? I was being deliberately decieved? All those layered models of the earth that are so diligently trotted out and explained in three (or occasionally, if we separate the core into an inner and outer core, four) layers are totally wrong?

Well, yes and no. I wasn’t being taught the correct structure of the Earth (at least right off). But when I think about how difficult it is to explain the concept of rock (or a solid) that flows to your average elementary-age child, I suppose I can’t get too upset. And since few people seem to get much instruction in Earth science beyond their elementary or middle school years, it’s easy to see why they cling to the “simple” explanation of the Earth’s structure. Unfortunately, unless they take an upper-level course in Earth science in high school or college, there’s not much opportunity to correct this. TV shows, especially on the Discovery and Science channels and the like, seem to be taking a good stab at it, but again, it’s a limited audience – and those shows are totally overwhelmed by all the other stuff that’s on the air nowadays.

Anyway, maybe it’s easier to just say that the mantle is molten rock and leave it at that, but I would appreciate it if the science teachers of the world (those that don’t already do this, that is) would take a stab at explaining that while the mantle is actually solid, the heat and pressure involved at that depth make it behave like a liquid. Much as I like having the opportunity to impart a little geologic knowledge to the people I meet, this particular misconception isn’t particularly difficult to head off before it becomes permanently implanted in someone’s understanding of the planet they live on.

Of course, this means the teachers had better be prepared with some material to help answer the inevitable “Why?” and “What do you mean, a solid can flow?” questions, but there’s nothing wrong with a healthy spirit of inquiry and they might even start some bright young minds on the path to a career in the geosciences.

As for pie and the Earth Sciences…well, I have the perfect example.

As you might have read in an earlier post, my first real experience with geology was on a 3 1/2 week-long field course to the Colorado Plateau. We started out in the Guadalupe Mountains of Texas and made our way up through New Mexico. On our way into Arizona, about 80 miles West of Socorro, NM on Highway 60, we came across a wonderful place:

Pie Town, New Mexico!

Yes, by golly, there’s actually a Pie Town. And yes, they sell pie – at The Daily Pie Cafe. And they tell you what kind of pie they have that day with…you guessed it, a “Pie Chart”.

I had Spiced Apple, and it was delicious. An experience not to be missed.