Rocks strewn across an ancient Martian shoreline could suggest that the Red Planet was more reminiscent of Earth in its past, according to recent findings. These rocks, uncovered by NASA’s Curiosity rover, contain high concentrations of manganese oxide. This discovery adds weight to the notion that Mars may have once harbored oxygen levels and environmental conditions conducive to life, similar to those found on Earth.
Manganese, often overlooked, played a crucial role in the development of life on our planet. Geological records show that it was abundant in rocks and oceans prior to the emergence of early life forms around 4 billion years ago, laying the groundwork for the oxygen essential for most life as we know it.
Yet, the perplexing aspect arises from the fact that the known methods for producing manganese oxide necessitate either copious oxygen or the presence of microbial life. However, there is scant evidence supporting the existence of significant oxygen levels on Mars, and none at all for microbial life. This leaves scientists at a loss as to how the chemical formed within the recently discovered Martian rocks.
Forming rocks rich in manganese oxide “is easy to do on Earth because of microbes and because of oxygen — which [also forms] because of microbes — so it all points back toward life,” lead study author Patrick Gasda, a research scientist at Los Alamos National Laboratory in New Mexico, said in an interview with Live Science. “We of course have no evidence of life on Mars, so if we’re trying to form oxygen in a fully abiotic system, our current understanding of Mars doesn’t explain that.”
While traversing through the heart of Gale crater, a vast ancient lake bed spanning 96 miles (154 kilometers) in diameter, the Curiosity rover stumbled upon these heavily weathered rocks. Since 2012, the rover has been diligently exploring this terrain. Using its ChemCam instrument, Curiosity effectively “sniffed out” the presence of manganese oxide within the rocks by vaporizing minuscule fragments with a laser and subsequently analyzing the resulting plasma cloud. The compound comprises nearly half of the rocks’ chemical composition, as detailed in a recent study published in the journal JGR Planets.
In the area where Curiosity stumbled upon these newfound rocks, the rover noted a modest elevation shift of 10 to 15 meters (33 to 49 feet). While this may seem minor compared to the considerable distances Curiosity has traversed over the years, it carries significance, as Gasda explained to Live Science, suggesting something noteworthy occurring in that location. The texture of the rocks in the vicinity where the new sandstones were discovered seems to have undergone a transition from “curved” to “flat-lined.” Gasda and his team interpret this change as indicative of a river channel expanding into a lake, adding another layer to the geological narrative of Gale Crater’s ancient history.
“That means we’re at the shore of the lake or near the shore of the lake,” Gasda said. He noted that this interpretation is uncertain due to limited data, because Curiosity drove past the region just once. “That made the interpretation really challenging, but this is our best hypothesis,” he added.
Should the hypothesis hold true, the rocks could have been deposited in the area when the flow of the river decelerated upon reaching the lake, akin to the accumulation of manganese-oxide-rich rocks observed along the shores of shallow lakes on Earth. This parallel offers an intriguing glimpse into the potential geological processes at play within Gale Crater, hinting at similarities between Martian and terrestrial environments despite the stark differences in their current states.
The newfound rocks are “another line of evidence for liquid water on Mars in the past, which is beneficial 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 newfound 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 lower-oxygen period and a higher-oxygen period. “The impact of manganese oxides on our understanding of such a transition, however, have been overstated, here and in prior work,” he told Live Science.
Catalano contributed to a study in 2022 that discovered manganese oxide could form readily under conditions resembling those found on Mars, even without the presence of atmospheric oxygen. This study, conducted through laboratory experiments, demonstrated that elements like chlorine and bromine, which were abundant during Mars’ early history, could facilitate the conversion of dissolved manganese in water into manganese oxide minerals. This groundbreaking finding presented an alternative pathway, distinct from oxygen, that could account for the existence of rocks similar to the recently discovered ones on Mars.
“There are several life forms even on Earth that do not require oxygen to survive,” Kaushik Mitra, a geochemist at the University of Texas at San Antonio who led that study, said in a statement in 2022. “I don’t think of it as a ‘setback’ to habitability — only that there were probably no oxygen-based lifeforms.”
