Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, Washington, DC, 20015 United States
Department of Geological Sciences, Brown University, P. O. Box 1846, Providence, RI 02912 United States
Geological Survey of Canada, 615 Booth Street, Ottawa, ON K1A 0E9 Canada