According to a study published Monday in the journal Nature Geoscience, the sulfate salts were detected in sedimentary rocks dated to between 3.3 and 3.7 billion years ago. Researchers have previously found other evidence of salt sediments on other parts of the Martian surface. However, this is the first time that researchers have seen evidence of sulfate salts in the Gale Crater.
“The deposits are consistent with early diagenetic, pre-compaction salt precipitation from brines concentrated by evaporation, including magnesium sulfate-rich brines from extreme evaporative concentration,” the study noted.
Scientists believe that the sulfates were left over after ancient brines, which may have once contained life forms, evaporated during the Hesperian Period on Mars, in which extensive volcanic activity and catastrophic flooding took place, eventually leaving the planet with a much more arid climate.
"The relatively low solubility of calcium sulfate minerals results in their widespread production during evaporation," the authors explained in the study, "while less common magnesium sulfate and chloride minerals represent terminal evaporation."
The authors also noted that hypersaline lakes on Earth are filled with life, which could mean that the salty ponds on Mars were inhabited by bacteria or similar microbial life.
"Sulfur is a basic element for life," study lead author William Rapin, a scientist at the California Institute of Technology in Pasadena, told Space.com. "And we show that there was sulfate available in the water."
The study also found sulfates located in the shallow sections at the fringes of the Gale Crater, meaning there may have been “segmentation of the Gale lake into discrete ponds, including those where extremely evapo-concentrated brines might form.”