1. Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015
2. Sagan Fellow, NASA Hubble Fellowship Program, Space Telescope Science Institute, Baltimore, MD 21218
3. Department of Philosophy, University of Colorado, Boulder, CO 80309
4. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125
5. Earth Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan
6. Blue Marble Space Institute for Science, Seattle, WA 98104
7. Department of Astronomy, Cornell University, Ithaca, NY 14853