1. Department of Geology and Geophysics, 1215 W. Dayton St., University of Wisconsin Madison, Wisconsin 53706, Microbial Insights, Inc. 2340 Stock Creek Blvd., Rockford, Tennessee 37853, Haley & Aldrich 103 Newhaven Rd. Oak Ridge, Tennessee 37830, and Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, MSIN K8-96 Richland, Washington 99352