Emily Chan
The first is that the carbonates materialized after a series of wet and dry cycles within the crater. In the second, the carbonates developed in salty water in cold, icy conditions at Gale.
“Wet-dry cycling would indicate alternation between more habitable and less habitable environments, while cryogenic temperatures in the mid-latitudes of Mars would indicate a less habitable environment where most water is locked up in ice and not available for chemistry or biology, and what is there is extremely salty and unpleasant for life,” said Jennifer Stern, a study co-author.
These climate scenarios have been proposed before, but this is the first time that isotopic evidence from rock samples has been used to support the scenarios.
The heavy isotope values in the Martian carbonates are much higher than the carbonate minerals on Earth. They also have the heaviest oxygen and carbon isotope values of any recorded materials on Mars.
According to the team, the wet and dry and the cold and salty climates are both needed to form such carbon- and oxygen-heavy carbonates.
The heavy isotope values were likely driven by an extreme degree of evaporation and then were preserved. Over time, the process rendered Mars uninhabitable.
The details of the study were published in the Proceedings of the National Academy of Sciences.
