1. Lawrence Berkeley National Laboratory, Earth Sciences Division, 1 Cyclotron Rd., M.S. 90-1116, Berkeley, California 94720. E-mail: tmdaley@lbl.gov; maschoenberg@lbl.gov; jrutqvist@lbl.gov.
2. Formerly Lawrence Berkeley National Laboratory, Berkeley, California. Presently Chevron ETC, 6001 Bollinger Canyon Rd., San Ramon, California 94583. E-mail: knih@chevron.com.