1. Institute for Earth and Space Exploration, University of Western Ontario, London, Canada.
2. Department of Earth Sciences, University of Western Ontario, London, Canada.
3. UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.
4. Department of Biology, Georgetown University, Washington, DC, USA.
5. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA.
6. Department of Earth Sciences, University of Southern California, Los Angeles, California, USA.