ON THE GEOMICROBIOLOGY OF EVAPORITES–A GEOPHYSIOLOGICAL OUTLOOK ON PLANETARY EVOLUTION

Microbiology and geoscience today are seen as intimately coupled. We describe the potential of microorganisms in evaporitic environments. Fossil and recent evaporitic environments are characterized by stromatolitic biofilm and microbial mat structures. The latter are the most important remains of life on planet Earth. Evaporitic systems house on the one hand a large fraction of the genera of the archaea, which can be divided into extreme halophiles, methanogens and extreme thermophiles. Further microbial induced sedimentary structures (M.I.S.S.) often witness extremely evaporative sequences in the sedimentary record. These may also include the so-called elephant skin structures recorded from the Ediacara series in Australia. Extreme halophiles (cyanobacteria, phototrophs, fungi, animals) created sedimentary structures occurring in several cataclysmic periods of Earth history such as Late Precambrian, Permian, Tertiary and recent environments. The principle of poikilotroph and poikilophilic microbiota as a key to survival in truly extreme environments with extremely changing conditions is developed. Archaea, cyanobacteria and fungi as the most important lineages of early life may have survived not only periods of draught but also of a "snow ball world” (deep frozen oceans and continents) with salts accumulating even under deep freeze stress. Organic carbon and carbonate carbon proxies in evaporitic systems pose many enigmatic problems for the interpretation of fossil ecosystems as well as some sedimentary sequences derived, which are not well understood as yet. Evaporitic sequences on Earth may well be compared to the harsh conditions on Mars, where liquid water at the surface is an exception but water availability may be regulated by the rules of survival under poikilophilic conditions. The true champions of survival of life on Mars may be compared to evaporite associated phototroph bacteria, cyanobacteria, fungi and perhaps some arthropoda. Structural and geomorphologic elements of such evaporitic sequences will be analyzed and compared to conditions on other planets.