1. Geosciences Department, State University of New York Stony Brook, New York 11794-2100 School of Chemistry, University of Birmingham Birmingham, B15 2TT, UK Physics Department, Brookhaven National Laboratory Upton, New York 11973-5000 Central Research and Development, DuPont Company Experimental Station, P.O. Box 80262 Wilmington, Delaware 19880-0262 Department of Earth and Space Science Osaka University, Toyonaka, Osaka 560-0043, Japan