LOW LEVELS OF LIFE IN THE HYPERARID CORE OF THE ATACAMA DESERT

Within the driest part of the Atacama there exists a region with "Mars-like" soil (Navarro-Gonzalez et al. 2003). There are three characteristic that make these soils Mars-like: 1. There is very low levels of organic material and the organics that are present are refractory. They do not decomposed at the temperatures reached by the Viking GCMS. 2.There are virtually no detectable soil bacteria either by culture or DNA amplification (Navarro-Gonzalez et al 2003) or by Limulus Amebocyte Lysate (LAL) (M. Turnbull private communication). 3. There is present in the soil an oxidizing agent that equally oxidizes L and D organics. Soils to the south of the arid core region do not show these characteristics. The entire Atacama is arid and receives very little rain. However many locations in the desert receive marine fog providing sufficient moisture for hypolithic algae, lichens and even cacti (Rundel et al. 1991, Warren-Rhodes et al. 2005). However in the region south of Antofagasta the coastal range blocks the marine fog. The crest-line of the coastal range averages 2500 m for about 100 km south of Antofagasta. The region that is in the "fog shadow" of this high coastal crest-line is the region that contains the Mars-like soils. The transition between bacteria-rich soils and the Mars-like soils is not yet understood. Preliminary data suggests that the transition is patchy. In the extreme arid core the soil is dominated by Mars-like conditions with isolated islands of bacteria-rich soil. Moving toward wetter regions, these isolated island presumably become more numerous and eventually merge for form the continuously habitable soils we observe in the regions of the Atacama the receive >25 mm/yr of rain. The arid core area the patchiness could follow to geological patterns in the soils, or could follow subtle environmental patterns of water availability, or the patchiness could be an intrinsic response of the microbial ecosystem. The Atacama desert, one of the oldest and driest deserts on the Earth, provides an analog for life in dry conditions on early or present Mars. Our biological and chemical results suggest that if the Viking lander had landed in the arid core region of the Atacama it would have been unable to detect any evidence of life. Indeed, the landers instruments would have produced results similar to what they produced on Mars.