The Limits of Life

Antarctic studies showed scientists that cold itself is not necessarily fatal to life. Life can tolerate very low temperatures and the process of freezing. But problems occur when low temperatures persist for long periods of time.

But how much water does life need to survive? - "At the moment, we do not know the limit of life along the aridity gradient. Organisms may have several strategies to cope. Some organisms become desiccated; others can live with very little water. Some organisms, like the common mold, can take up water from the atmosphere if the humidity is above a certain level. But these strategies aren't very well explored, and the conditions are very difficult to replicate in the lab.", says a NASA microbiologist. (Source: NASA)

The Atacama Desert of Chile is the driest desert on Earth with temperature extremes that can vary by as much as 50 degrees Celsius (90 degrees Fahrenheit) within a single 24-hour period. At its center is a place climatologists call absolute desert. There are sterile, intimidating stretches where rain has never been recorded, at least as long as humans have measured it.

The desert has been in a super-dry state far longer than any other location on Earth. A team of  British scientists reports the existence of hyper-arid conditions in the desert have lasted at least 20 million years. This is much older than other hyper-arid regions, such as the Dry Valleys of Antarctica (10-11 million years) and the Namib desert in Africa (5 million years). (Source: BBC)

It is one of the most lifeless environments on the planet. There is no blade of grass or cactus stump, not a lizard, not a gnat. But you will see the remains of most everything left behind. The desert may be a heartless killer, but it's a sympathetic conservator. Without moisture, nothing rots. (Source: National Geographic)

NASA researchers consider the Atacama Desert an analog environment for Mars, and have used this environment as proving grounds for future Mars instrumentation aiming to detect signatures of life. In addition to water limits, the scientists are also hoping to determine how organisms develop defenses against UV radiation. Such radiation would be yet another limit to life on Mars, which experiences more intense radiation than Earth. (Source: id.)

In 2003, a team of researchers published a report in Science Magazine titled "Mars-like Soils in the Atacama Desert, Chile, and the Dry Limit of Microbial Life" in which they duplicated the tests used by the Viking 1 and Viking 2 Mars landers to detect life, and were unable to detect any signs in Atacama Desert soil.  (Source: Wikipedia)

However, identifying living microorganisms and/or fossils adapted to a very hostile environment like the Atacama desert  should provide leads to establish detection criteria and strategies for Mars or other planetary bodies. Hence, search continued.

In 2007 it has been found that some microbial life exists on the thin layer (varnish) on the surface of rocks. Three years later another research has been published showing that microbial life exists also in gypsum crusts which are found in locations where there is high relative humidity at night. The environment there provides enough water for a virtual menagerie of microbes to inhabit the gypsum. (Sources: Wondermondo and Astrobiology Magazine)

The results have important implications for the habitability and the potential for life in extremely dry environments on Earth and other planets. Since chloride salts have the same physical properties on Earth and on Mars, it is possible that the same deposits on Mars provided habitable conditions for microorganisms adapting to the increasingly arid condition. (Source: International Microbiology)

I guess, we will continue to ask: How does life begin and evolve, does life exist elsewhere in the universe, and what is the future of life on Earth and beyond? (Source: NASA Astrobiology Roadmap)