1. Department of Earth and Planetary Science, University of California, Davis, California 95616, USA
2. Department of Earth and Environmental Sciences, California State University, Fresno, California 93720, USA
3. U.S. Geological Survey, Menlo Park, California 94025, USA
4. Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709, USA
5. Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA
6. Exxon Mobil, Houston, Texas 77389, USA
7. School of Oceanography, University of Washington, Seattle, Washington 98105, USA