Ehlmann and colleagues published their work today in the journal Science.
For now the exposed mineral layers don't reveal enough carbonate to confirm or deny the theory that early Mars had a thick, carbon dioxide-rich atmosphere, noted Scott Murchie, a researcher on the Mars orbiter team based at Johns Hopkins University in Maryland.
However, further study of the Martian minerals could "help us understand whether what's preserved on the surface today is possible evidence of past life," Murchie said.
Study leader Ehlmann agreed. The carbonate-containing regions of Mars "would have been a pretty clement, benign environment for early Martian life, and I think it is a great area to look in future investigations of Mars's habitability," she said.
The Whole Elephant
Earlier this year Andrew Knoll, of Harvard University, co-authored a study based on mineral data from the Mars rover Opportunity.
Early Mars likely supported a salty, toxic stew—waters that would have been inhospitable to known forms of life—the earlier study said.
Knoll, who was not involved in the new study, said that if the carbonates found are definitely from early Mars, they would indicate that—at least locally—the waters would have been neutral enough for life.
But, he said, "there are probably a hundred different criteria by which we would assess the habitability of Mars."
Finding carbonates is not enough to say with any certainty that Mars would have supported life in its past.
"There's a whole history of papers where people look at features on the elephant and try to describe the whole elephant," Knoll said.
"We've been very fortunate in recent years with the rovers and orbiters on Mars to make observations that have changed the way we think about the planet," he continued.
"Nonetheless, there's still a lot we don't know, especially about the origins of life."
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