Why Are Students Not Very Interested in Petrology?

Petrology is an exciting field, but fewer and fewer students see it that way in spite of many important unsolved petrological questions about how the Earth works (e.g., how are continents made? do plumes exist? how do volcanoes affect the environment?). Here I outline a personal view of how this came to be and what we might do about it.

If textbooks are any guide, petrology is taught today much as it was decades ago. Textbooks focus on classification, phase diagrams, layered mafic intrusions, fractional crystallization, freakish alkaline rocks, etc.; labs are typically heavy on mineral identification, classification, and optical mineralogy. These topics are rarely relevant to the big questions. Conversely, textbooks have little on isotope geology, geochronology, granites, in-situ analytical methods, etc., topics that underlie much of the exciting petrological research going on today. Further, textbooks commonly present difficult concepts (e.g., phase equilibria) out of context; we give the students tools without telling them what those tools are used for, expecting them to put it all together before the final exam. Finally, textbooks present igneous and metamorphic petrology as two separate and unrelated subjects, leading to a rarely bridged chasm between fields that are closely related.

A better approach might be to lead students to ask big questions, and then teach them the tools needed to answer those questions. For example, my students use petrological databases to discover that igneous rocks in the oceans are far more uniform in composition than continental ones, and then learn tools (geochemical modeling, isotopes) that tell us why. I interweave igneous and metamorphic petrology, talking about contact metamorphism while talking about plutons, etc. Getting students to think about petrologic processes is a priority; descriptive systematics is not. Students learn fewer facts but seem far more engaged.