1. A. H. Knoll is in the Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
2. M. R. Walter is at the Australian Centre for Astrobiology, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia.
3. G. M. Narbonne is in the Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada.
4. N. Christie-Blick is in the Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA.