What does the core/mantle boundary look like?

Suzanne Baldwin
Syracuse University
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This activity explores how earth scientists infer what materials are present at the core mantle boundary and what this boundary might look like. It provides students with the opportunity to contribute to the scientific debate regarding what the core mantle boundary looks like, it's composition, structure, and properties.

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This activity can be used in an undergraduate Mineralogy course.

Skills and concepts that students must have mastered

Before beginning this activity the students will have learned and be able to answer the questions 'what minerals are in the core and how do we know?" and "what minerals are in the mantle and how do we know?" See attached file for specific topics to cover prior to assigning this activity.

How the activity is situated in the course

Introductory Geology is a prerequisite for mineralogy and introductory chemistry is a corequisite. This activity follows discussions of minerals of the core and mantle, approximately one third through the semester. It is assigned as a take home exam question and prior to discussions of the crust and surface minerals.


Content/concepts goals for this activity

Goals of this study are to integrate data sets from cosmochemistry, experimental petrology, and tomography to develop a model for the structure and composition of the core-mantle boundary. Students will gain an appreciation of how we learn about this boundary within the deep Earth when we have no direct evidence for what exists at the core-mantle boundary.

Higher order thinking skills goals for this activity

These skills include formulating a hypothesis, and formulating ideas for testing the proposed hypothesis. Students will also contribute to a debate for which the answer is unknown. They will learn that they are able to contribute to this debate.

Other skills goals for this activity

Reading the literature, drawing schematic figures, working in groups and presenting results are other skill goals.

Description of the activity/assignment

We will begin with a review of what minerals are inferred to be in the core and what minerals are inferred to be in the mantle. Students will then sketch what they think the core-mantle boundary looks like. Students will make observations of samples of pallasite (identify texture and compositions). Next using phase diagrams (e.g., Fe, olivine, post-perovskite) determine the temperatures and pressures at which these minerals might be stable at the core-mantle boundary. What is the coordination number for these inferred phases at this boundary? Are the phases liquid, solid or both? Next assess and describe how P and S wave velocities change at the core-mantle boundary.

Determining whether students have met the goals

Students will submit two drawings of what they think the core-mantle boundary looks like ( the drawing that they started off with and the one they revised following this learning activity). They will submit a paper (no longer than 2 pages) discussing the indirect evidence they have used to generate their final figure. They will share with the group their results.

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