A collection of rocks scattered along the ancient coastline of Mars could mean the Red Planet was once much more Earth-like than scientists previously thought.
Rocks found by NASA’s Curiosity rover are unusually rich in manganese oxide, a chemical that adds to growing evidence that once habitable Mars may have had Earth-like oxygen levels and life-friendly conditions early in its history, they say the scientists.
NASA calls Earth’s manganese “an unsung hero in the evolution of life.” Scientists know from the geologic history of our planet that manganese was abundant in rocks and oceans before the appearance of the earliest forms of life about 4 billion years ago, and that paved the way for oxygen on which most life now relies.
However, the only known ways to produce manganese oxide involve abundant oxygen or microbial life. But there is no strong evidence of the former on Mars, nor of the latter, leaving scientists puzzled as to how the chemical formed in the newly discovered rocks.
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The formation of manganese oxide-rich rocks “is easy to do on Earth because of the microbes and because of the oxygen—which [also forms] because of the microbes – so everything points back to life,” the study’s lead author Patrick Gasda, a researcher at Los Alamos National Laboratory in New Mexico, told Live Science. “Of course, we have no evidence of life on Mars, so if we’re trying to form oxygen in a completely abiotic system, our current understanding of Mars doesn’t account for it.”
The Curiosity rover encountered heavily eroded rocks as it passed through the middle of Gale Crater, a 96-mile (154-kilometer) wide ancient lake floor that the rover has been exploring since 2012. The rover’s ChemCam instrument “sniffed” manganese oxide in rocks by vaporizing tiny particles with a laser and then analyzing the resulting plasma cloud. The compound makes up nearly half of the rocks’ chemical composition, according to the new study, which was published last week in the journal JGR Planets.
Where Curiosity found the new rocks, the rover recorded a 10 to 15 meter (33 to 49 ft) change in elevation. While that’s small compared to the hundreds of meters Curiosity has climbed over the years, it “points us to something special going on at this location,” Gasda told Live Science. The texture of the rock where the new sandstones were found appears to have gone from “curved” to “flat line”—a change that Gasda and his colleagues interpret as a river channel opening into a lake.
“That means we’re on the lakeshore or near the lakeshore,” Gasda said. He noted that this interpretation is uncertain due to limited data, as Curiosity has only passed by the region once. “That made the interpretation really challenging, but that’s our best hypothesis,” he added.
If the hypothesis is correct, the rocks may have been dumped in the area when river water slowed as it entered the lake, similar to the manganese oxide-rich rocks that were it is found on the shores of shallow lakes on the ground.
The newly discovered rocks are “further evidence of liquid water on Mars in the past, which is useful for life,” Manasvi Lingam, an astrobiologist at the Florida Institute of Technology who was not affiliated with the new research, told Live Science. “This work provides evidence in favor of habitability.”
However, not everyone agrees that the newly discovered rocks indicate an oxygen-rich Mars. According to Jeffrey Catalano, a professor of earth, environmental and planetary sciences at Washington University in St. Louis, who was not involved in the study, the presence of oxidized rocks could help scientists understand whether Mars, like Earth, went through a “punctuated transition” from a period of lower oxygen content and a period of higher oxygen content. “However, the impact of manganese oxides on our understanding of such a transition has been overestimated here and in previous job,” he told Live Science.
Catalano was part of 2022 study that the exposed manganese oxide can easily form under Mars-like conditions without atmospheric oxygen. This research, which is based on laboratory experiments, shows that elements such as chlorine and bromine, which were abundant on early Mars, converted manganese dissolved in water into manganese oxide minerals. This discovery offers an alternative to oxygen that could explain rocks like those newly discovered on Mars.
“There are several forms of life even on Earth that do not need oxygen to survive,” Kaushik Mitrageochemist at the University of Texas at San Antonio, who led this study, said in a statement in 2022. “I don’t think of this as a ‘barrier’ to habitability – just that there probably wasn’t any oxygen-based life.”
