830-million-year-old organisms found in rock salt, and they may be alive

Instead, organic material can only survive in the small amounts that may be trapped inside the salt as it crystallizes. Called fluid inclusions, these are small samples of the waters in which the salt crystallized and can be used to study water and atmospheric temperatures as well as water chemistry at the time of the mineral formation. 

The researchers studied a sample from the Browne Formation in Australia, an area characterized by sedimentary layers of rock with extensive halite formations. This is indicative of a salty sea that existed millions of years ago. 

Using non-invasive methods such as transmitted-light and ultraviolet photography, the geologists found traces of organic solids and liquids which are consistent with both prokaryotic as well as eukaryotic organisms. Interestingly, while the range of fluorescence exhibited displayed signs of organic decay, it also demonstrated signs of unaltered organic material, which is suggestive of modern organisms, Science Alert reported. 

How this could help us on Mars

It is even possible that the organisms are alive as the fluid inclusions serve as microhabitats for them. A separate study from 2002, showed that microorganisms in 250-million-years-old halite formations can survive radiation exposure. We haven't found looked for life in halites older than this. But by undergoing metabolic changes and using organic and dead cells as nutrient sources, these organisms can survive even the roughest of conditions inside the fluid inclusion for many more years. 

The researchers are of the opinion that their findings could have implications for research on Mars, which has structures similar to the Browne Formation in Australia. 

"Ancient chemical sediments, both of terrestrial and extraterrestrial origin, should be considered potential hosts for ancient microorganisms and organic compounds," the researchers write in the paper published in the journal Geology.

Abstract: 
Primary fluid inclusions in bedded halite from the 830-m.y.-old Browne Formation of central Australia contain organic solids and liquids, as documented with transmitted light and ultraviolet–visible (UV-vis) petrography. These objects are consistent in size, shape, and fluorescent response with cells of prokaryotes and eukaryotes and with organic compounds. This discovery shows that microorganisms from saline depositional environments can remain well preserved in halite for hundreds of millions of years and can be detected in situ with optical methods alone. This study has implications for the search for life in both terrestrial and extraterrestrial chemical sedimentary rocks.