You Must Remember This …

Lisa A. Rossbacher

It’s something both first-year geology students and old-and-gray professional geologists have to face: Geology has some things you simply have to memorize. There’s no way around it. Moh’s hardness scale. The geologic time scale. The order of the planets. The visible part of the electromagnetic spectrum. And of course, depending on your specialty, there are bound to be other facts you just have to memorize, such as the order of sizes of rock materials, or the order of crystallization of igneous rocks.

Cue the mnemonic device. As a noun or adjective, this is a device that helps with memory. In fact, that’s literally what the word means in the original Greek.

Mnemonic devices in the geosciences aren’t always politically correct, but they’ve helped more than one student through an exam.

“The Girls Can Flirt And Other Queer Things Can Do” is the classic way of remembering Moh’s hardness scale, from 1 to 10 on the scale. (I won’t insult the readers by reminding you what the corresponding minerals are — except to note that the orthoclase feldspar can be tricky, because it’s an “o,” not an “f.”)

Other mnemonic devices are helpful, too. The Web site offers some options, like the following mechanism to remember the order of the geological time periods: “Cows Often Sit Down Carefully. Perhaps Their Joints Creak? Persistent Early Oiling Might Prevent Painful Rheumatism.” If you need help with the Precambrian, well, you may want to invoke a “Pregnant Camel.” And if you’re living in the Holocene, rather than Recent, you might need to “Prevent Poor Health,” instead of “Prevent Painful Rheumatism.” (Do note that this Web site is European, and they do things a little differently than in the United States.)

I’ve heard more than my share of such sayings over the years. More elegant examples exist for remembering the geologic periods, including: “Cold Oysters Seldom Develop Many Precious Pearls, Their Juices Congeal Too Quickly,” or “Come Over Some Day, Maybe Play Poker. Three Jacks Can Take Queens.” Several useful ways to remember the Cenozoic epochs include: “Pigeon Egg Omelets Make People Puke Heartily.” Or this: “Phooey! Even Old Men Play Polo, Hey?”

In the less politically correct realm: Mnemonic devices for the Paleozoic have sexual overtones, the Mesozoic is irreligious, and the Cenozoic is scatological. Tortured? Yeah.

Some mnemonics have very special purposes. The phrase “Know The Canyon’s History. Study Rocks Made By Time,” makes more sense than most mnemonics, and it is a valuable stratigraphic reminder on a rafting trip down the Grand Canyon.

One of the most popular options for the order of the planets used to be “My Very Educated Mother Just Served Us Nine Pizzas,” which worked when Pluto was farther away from the sun than Neptune. That wasn’t true from 1979 to 1999, but it is valid for another 240 years now. Or it would have been, if the International Astronomical Union hadn’t banished Pluto from the planetary lineup altogether (see Geotimes, October 2006). So now, school children get pasta rather than pizza: “My Very Excellent Mother Just Sent Us Noodles.” I admit that I never used a mnemonic device for the order of the planets. I just muscled my way through that sequence. But the geologic time periods are certainly a different story.

Mnemonic devices can help with more than just memorizing lists. Most geologists make a quick reference to one when they distinguish between stalactites and stalagmites. One of these features “sticks tight” to a ceiling, or hangs down like tights on a clothesline, and the other evokes bugs, like mites, crawling around on the ground. Alternatively, one of these words includes the letter “g” (for ground) and the other a “c” (for ceiling).

We can’t forget the electromagnetic spectrum, which may have the very first mnemonic device you ever learned. Once upon a time, only physicists were concerned about this. With the growth of geographic information systems and new forms of remote sensing, geologists are increasingly involved in imagery at various wavelengths. Enter our old friend, “Roy G. Biv.” He’s a long-standing favorite for a way to remember the sequence of colors at (decreasing) wavelengths: Red, Orange, Yellow, Green, Blue Indigo, Violet. And here’s a scary thought: I know more than one person who organizes the clothes in her closet using Roy as a guiding principle.

Mnemonics are our friends. As one colleague notes on his Web site for an introductory geology class — right after he emphasizes, “This WILL be on the exam” — “If you have a strong stomach, there are many more memorable mnemonics out there.” This observation fits my own experience. Once, when I taught a large physical geology course, I asked the students to invent their own mnemonic devices for the geologic periods. I offered one option, but I asked them to create something that was memorable for them. And I asked them to write it down to share with me. Foolishly, I thought I would be able to share these creative learning tools with the class…

I never did that again. Not only could I not share most of the submissions with the other students, but a few made me blush. Some mnemonic devices are, well, personal. And to that end, I’m not sharing my own devices. If you need a couple, though, there are a bunch of good Web sites out there with catchy (and weird) mnemonic devices, but sometimes the best option is the one you come up with on your own.

Rossbacher, a geologist, is president of the Southern Polytechnic State University in Marietta, Ga. E-mail:

Planets redefined: Pluto gets demoted,” Geotimes, October 2006 

Geotimes, November 2007

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