Steven B Shirey¹, Lara S Wagner¹, Michael J Walter², Peter E van Keken¹ and D. Graham Pearson³, (1)Carnegie Institution for Science, Department of Terrestrial Magnetism, Washington, DC, United States, (2)Carnegie Institution for Science, Geophysical Laboratory, Washington, DC, United States, (3)University of Alberta, Earth & Atmospheric Sciences, Edmonton, AB, Canada