1. Mail Code A0220. University of California, San Diego, La Jolla, CA 92093, USA
2. NASA Specialized Center of Research and Training in Exobiology, Scripps Institution of Oceanography, University of California, San Diego
3. Departments of Chemistry and Molecular Biology, Scripps Research Institute, La Jolla, CA 92037, USA
4. Departamento de Biología, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, México 04510, DF
5. Department of Chemistry, Mail Code GRB-0506, University of California, San Diego
6. Chemical Evolution Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA