Timothy D Jones, Carnegie Institution for Science Washington, Washington, United States, Nathan Sime, Carnegie Institution for Science Washington, Department of Terrestrial Magnetism, Washington, United States, Ross Maguire, University of Maryland, College Park, Department of Geology, College Park, MI, United States, Peter E van Keken, Carnegie Institution for Science, Department of Terrestrial Magnetism, Washington, DC, United States and Jeroen Ritsema, Univ Michigan, Ann Arbor, MI, United States