Analogy use in textbook introductions to isostasy: Presentations, perceptions and physics

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In teaching, analogies can be used to support the introduction of a new concept or idea with reference to a more familiar one. This relies on the learner’s correct understanding of the (supposedly) familiar situation, their identification of the relevant similarities (structural relations) between the two situations, and of the limits of the similarities. Without these, analogies may reinforce or introduce misconceptions. Through content analysis of 14 introductory textbooks, semi-structured interviews with four students, and analysis of two analogies, we explore how analogies are used as part of introductions to isostasy in introductory geoscience textbooks. Analogies were ubiquitous, but prior knowledge of the source domain was typically assumed and the majority were not elaborated (explained to the learner). Interviews indicate that, in the absence of sufficient elaboration, students turn to superficial similarities for clues on how to apply the analogies. Many textbooks used analogies amenable to this approach, indicating an alignment between textbook strategy and student reactions. However, giving precedence to superficial similarities over explicit elaboration of structural relations may favor a novice approach to learning. Analyzing an analogy using free-body diagrams demonstrates how an apparently relevant analogy can introduce misconceptions, both in terms of the underlying physics (introducing a fictitious force) and the Earth application (unnatural behavior of the lithosphere) when not sufficiently, or correctly, elaborated. We conclude that the introductory textbooks place much of the responsibility for appropriate use of their analogies, and for avoiding misconceptions, on the learners and their teachers.