1. Institute of Human Origins Geochronology Center, 2453 Ridge Road, Berkeley, CA 94709
2. Instituto Astrbnômico e Geofisico, Universidade de Sāo Paulo, 05508 Sāo Paulo, Brazil
3. Department of Earth Sciences, University of California, Santa Cruz, CA 95064
4. Centre Geologique et Geophysique, 34060 Montpelier Cedex, France