1. J. F. Adkins and E. A. Boyle, Department of Earth, Atmosphere and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2. H. Cheng and R. L. Edwards, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA.
3. E. R. M. Druffel, Department of Earth System Science, University of California at Irvine, Irvine, CA 92697–3100, USA.