For teachers, geology is a hard subject. Not because of the subject matter, which is popular and fascinating. What makes it hard is the kids looking for easy credits, who come to class with heads full of misinformation.

Even a Harvard education won't set these people right. Maybe you saw a video made in 1988 that shows graduating Harvard seniors answering science questions, in which most of them said that the seasons are caused by the Earth moving closer and farther from the sun. They were quite sure of themselves, but quite wrong. How did they get so far while staying so ignorant?

John DeLaughter, who teaches Earth science at Northwestern University, has been studying students to learn how they learn. He and his colleagues start by testing an incoming class on what they think they know. In a typical class taking a "rocks for jocks" course for nonmajors, almost half of the students think that the Moon revolves around the Earth once a day. And five in six students don't know that the seasons result from the Earth's tilt on its axis. (These and other wrong beliefs are laid out on the Web site of DeLaughter's colleague, seismologist Seth Stein.)

Psychologists have some insights about how people learn. Jean Piaget concluded from his studies of children that people put together a mental model of how the world works. They check their model against the evidence around them, but tend to favor things that support the model. Facts that partly contradict the model, people shrug off. After a while, if a lot of troublesome facts pile up, the model is cast into doubt and people set it aside. This makes people put together a new and better model, and we go on from there.

An example might go like this: a three-year-old assumes all dogs are friendly, based on the ones at home. After getting bitten or hassled by strange dogs enough times, the kid revises this model: all dogs should be checked out first—maybe cats, too.

What this means for geology teachers is that students come to class with models of the world in their heads, and they'll resist changing them. And when they're looking for an easy grade to meet a science requirement, the resistance is greater. This is nothing to blame, just something to deal with.

A teacher deals with it by finding magic bullets that break those models—then the students' minds are open to thinking about the facts. For instance, when a student explains the seasons by how far the Earth is from the sun, the teacher asks, "So why is it summer in Argentina at the same time it's winter in Canada?" Then the student goes and learns the right answer.

But with a hundred students at a time taking Geology 101, with a hundred different sets of misbeliefs, there just aren't enough magic bullets. DeLaughter and his colleagues are finding that their model of Earth science education is broken, and the work of building a better one proceeds.

Science itself works much the same way—the scientific community settles on a model and happily works it out, shrugging off contradictions until they grow intolerable. Then anything goes for a while, until the community agrees on a new model. The philosopher Thomas Kuhn detailed this cycle in the 1960s, calling the model a paradigm and the process of finding a new model a scientific revolution or paradigm shift. (Plate tectonics came along just at that time, a textbook paradigm shift.) Science works better than the Geology 101 class because everybody works hard to stay in step with each other.

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