What does the core/mantle boundary look like?
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- Activity Description/Assignment:
In this exercise we will explore what the core-mantle boundary might look like. No one actually knows what this boundary looks like, so this is an opportunity for you to contribute to this debate. Since we can't observe materials at the core-mantle boundary directly, how can we know what's there? What minerals might be there? Are there solid and liquid phases? You will have an opportunity to explore the latest research on this topic to develop your own model for what the core-mantle boundary might look like.
1) To begin, draw a sketch of what you think the core-mantle boundary looks like. When you are finished hand this sketch in. (This will be an in class assignment to be turned in during lecture)
2) Next we will explore the recent literature to ascertain what phases might be present at the core-mantle boundary. Indirect evidence for what might be at the CMB comes from the fields of cosmochemistry, experimental petrology and seismic tomography. Some references to get you started are listed below.
Indirect evidence from cosmochemistry.Pallasites are a type meteorite that has often been used to infer what the CMB might look like. What minerals can you identify in the pallasite samples? For those who do not have access to pallasite samples, students can check out the pallasite samples for sale on the web (e.g., http://www.gizmag.com/the-fukang-pallasite--extraterrestrial-gemstones-for-sale/9134/picture/43667/)
Indirect evidence from experimental petrology. Using the phase diagrams of post-perovskite and perovskite, and Fe describe the P-T conditions inferred at the Earth's core mantle boundary. http://tristan.ferroir.free.fr/Post-perovskite.php
Indirect evidence from seismic tomography. (to be added) discussion of fate of subducted slabs, etc.
As you dive deep into your research on what materials might be at the core-mantle boundary, feel free to see me to discuss any questions you might have.
3) Finally, empowered with the results of your literature search, and from compiling all indirect evidence, make a revised sketch of what you think the core mantle boundary looks like. Your revised sketch is to be accompanied by a written description of its features with references to back up your inferences. This accompanying description should be no longer than 2 pages.
- Instructors Notes:
core-mantle boundary assignment (Microsoft Word 260kB Jan15 11)
- Solution Set: see above instructor's notes