1. Earth-Life Science Institute; Tokyo Institute of Technology 2-12-1-IE-1 Ookayama, Meguro-ku; Tokyo 152-8550 Japan
2. Co-60 Radiation Facility; Tokyo Institute of Technology 2-12-1-IE-1 Ookayama, Meguro-ku; Tokyo 152-8550 Japan
3. Department of Earth and Planetary Sciences; Harvard University; Cambridge, MA USA
4. Blue Marble Space Institute of Science; Seattle, WA USA