1. Atacama Life Chris McKay NASA Ames cmckay@mail.arc.nasa.gov

2. A transect from arid to extreme arid Yungay station, extreme arid 50 times drier than Death Valley 500 km south of Yungay, arid about as dry as Death Valley

3. Colonized Stones in the Atacama Desert Warren-Rhodes et al. Micro. Ecol. 2005

4. Crestline for the coastal range in the Atacama Desert

5. Rock garden Altamira Vineyard

6. Moisture mm/yr Life Mars-like soils Soil Bacteria Hypolithic algae Shrubs and insects 1 525 125 Desert ecosystems Gobi Desert Mojave Desert Biology wins reducing Photochemistry wins, oxidizing Nitrate deposits 0.2

9. Navarro-Gonzalez et al. Science, 2003

11. "Self-organized patchiness and the resource concentration mechanisms involved have been reported from various ecosystems, among which arid ecosystems are the most prominent." Rietker et al.2005, Self-Organized Patchiness and Catastrophic Shifts in Ecosystems. Science, 305, 1926-1929.

12. Hypothesis: Microbial Patchiness in the Atacama Desert is due to oxidant. 1.Constant and uniform production of oxidant. 2. If biological production of organics exceeds oxidant  habitable zone. 3. If biological production of organics is less than oxidant  not habitable zone. 4. Organisms in, or falling into, habitable zone grow creating positive feedback.

13. Moisture Bacterial Counts Biology>Oxidant Biology~Oxidant Biology<Oxidant

14. Implications Length scale of patchiness should vary with moisture. Soil organics will be patchy and correlate with soil organisms. Soil oxidant will be patchy and anti- correlated with organisms.