Saltwater can evaporate leaving evaporite deposits consisting of salts such as sodium chloride (halite) and calcium sulfate (gypsum). Within evaporates are fluid inclusions – small trapped pockets of water – that can provide a refuge for microbes for at least six months. Cyanobacteria trapped within dry evaporite crusts can continue to have low levels of metabolic function such as photosynthesis. These deposits also form fossils of the organisms trapped within. Although highly controversial, it has been claimed that bacteria might survive for millions of years in the fluid inclusions of salt deposits including evaporates. Intriguingly, such deposits have been found on Mars.
In fact parallels are being drawn between locations such as the Bonneville Salt Flats that surround the Great Salt Lake and Meridiani Planum on Mars where the Mars Exploration Rover Opportunity landed. Opportunity discovered that it was parked on top of an evaporate basin, the remnants of an ancient martian salty sea, just as the Great Salt Lake and surrounding flats are the remnants of a much larger, ancient body of water – Lake Bonneville – which drained away thousands of years ago. As the conditions on early Mars got colder and harsher, it lost liquid water through evaporation or sequestration into permafrost. Remaining bodies of water would have been increasingly salty places, and then finally all liquid water disappeared, and the salt deposits eventually lithified into the evaporate rocks the rover sees today. Any early martian microbe would have had to withstand a high salt environment and intense UV radiation.
The suggestion that Jupiter's moon Callisto may have an underground saline ocean (see Callisto, ocean and possible life) also raises the possibility that primitive life forms similar to terrestrial halophiles might be found there, as well as on the neighboring moon, Europa.
External linkHalophile genome sequenced (BBC)
Related categories• EXTREMOPHILES
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