The continuing search to find life-sustaining elements on Mars may have resulted in a promising find.
A recent study documents the discovery of salt deposits from an ancient lake which could have been home to some of the planet's last living organisms.
Scientists have dated the presence of liquid water there to about 3.6 billion years ago which is about 200 million years later than previous estimates of its last existence on Mars.
The theory is that as Mars became colder with less atmospheric pressure, any remaining water receded and froze at the poles.
See photos from the Curiosity rover on Mars:
Ancient lake could have been last site for martian life
This image from Curiosity's Mastcam shows inclined beds of sandstone interpreted as the deposits of small deltas fed by rivers flowing down from the Gale Crater rim and building out into a lake where Mount Sharp is now. It was taken March 13, 2014, just north of the "Kimberley" waypoint.
This March 25, 2014, view from the Mastcam on NASA's Curiosity Mars rover looks southward at the Kimberley waypoint. In the foreground, multiple sandstone beds show systematic inclination to the south suggesting progressive build-out of delta sediments in that direction (toward Mount Sharp).
This image shows inclined beds characteristic of delta deposits where a stream entered a lake, but at a higher elevation and farther south than other delta deposits north of Mount Sharp. This suggests multiple episodes of delta growth building southward. It is from Curiosity's Mastcam.
This evenly layered rock photographed by the Mast Camera (Mastcam) on NASA's Curiosity Mars Rover on Aug. 7, 2014, shows a pattern typical of a lake-floor sedimentary deposit not far from where flowing water entered a lake.
This image shows an example of a thin-laminated, evenly stratified rock type that occurs in the "Pahrump Hills" outcrop at the base of Mount Sharp on Mars. The Mastcam on NASA's Curiosity Mars rover acquired this view on Oct. 28, 2014. This type of rock can form under a lake.
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Brian Hynek, a research associate at the Laboratory for Atmospheric and Space Physics (LASP) at CU-Boulder and lead author of the study, explains, "Having a later stage of water on Mars is probably a good thing for the potential for life on that planet because it gave life more time to be conceived."
Other encouraging signs include salinity levels estimated to have been about eight percent of that found in Earth's oceans which is within range of sustaining life.
The 18-square mile expanse of chloride is located in an area called Meridiani, close to where the Mars Opportunity rover landed but out of its driving distance.