Biology
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p23b..08s&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P23B-08
Biology
4840 Microbiology, 5705 Atmospheres: Evolution, 5749 Origin And Evolution, 6225 Mars, 1800 Hydrology
Scientific paper
We simulated the major environmental stresses on and near the Martian surface and recorded their effects on microbial populations of E. coli and D. radiodurans. Viability rates were determined for the populations under the single and combined stresses of sub-zero temperature, low-pressure, and UV radiation in salt-water soil and fresh-water soil at variable depths, and in sea water. Our results demonstrate that E. coli and D. radiodurans can remain viable under these exposure conditions, but are most sensitive to low pressure. The effect of low pressure is lessened under sub-zero temperatures as microbial populations from both species appear to respond synergistically to these combined stresses. However, the low-pressure effects are so dramatic (much more so than from UV radiation), that microbial life near the surface of Mars appears unlikely if it shares the characteristics of the model organisms in our study. This finding is consistent with our earlier projection that single cell life would, if extant near the surface, most likely be dormant. Results from the Mars Exploration Rovers and orbiters confirm a picture of Martian environmental history as consisting of long periods of quiescence with extremely slow surface erosion punctuated by short-duration episodes of quasi-stable conditions (e.g. triggered by magmatic driven activity at Tharsis) of a considerably wetter and warmer environment, which likely included hydrothermal activity and ponded surface water bodies in the northern plains (e.g. from cataclysmic floods). This environmental history would have promoted the (1) origin of life as chemoautotrophs, some of which may have evolved into heterotrophs, (2) possible origin of phototrophs, (3) strong directional selection for enhancing chemoautotrophy and the development of alternative energy sources, (4) strong directional selection for life cycles alternating between dormant and proliferative forms, and (5) possible persistence of some chemotrophs and organisms using alternative energy sources below the Martian surface to the present time. Putative microbes may thrive in ground water, which we would expect to differ substantially from ancestral forms.
Diaz Bernard
Irwin Louis N.
Schulze-Makuch Dirk
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