Mars may have been more Earth-like than we thought, discovery of oxygen-rich rocks reveals

A collection of rocks scattered on an ancient shoreline on Mars might indicate that the Red Planet was once far more Earth-like than scientists previously thought.

The rocks, discovered by NASA's Curiosity rover, are unusually rich in manganese oxide — a chemical that adds to growing evidence that the once-habitable Mars may have sported Earth-like oxygen levels and life-friendly conditions early in its history, scientists say.

NASA calls manganese on Earth "an unsung hero in the evolution of life." Scientists know from our planet's geological History that manganese was abundant in rocks and in the oceans before the earliest life-forms emerged roughly 4 billion years ago and that it paved the way for oxygen that most life now relies on. 

The only known ways to produce manganese oxide, however, involve either abundant oxygen or microbial life. But there isn't strong evidence for the former on Mars, and none for the latter, leaving scientists puzzled by how the chemical formed in the newfound rocks.

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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, told 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."

The Curiosity rover came across the heavily eroded rocks while trekking through the middle of Gale crater, a 96-mile-wide (154 kilometers) ancient lake bed that the rover has been exploring since 2012. The rover's ChemCam instrument "sniffed" the manganese oxide within the rocks by vaporizing tiny bits with a laser and then analyzing the resulting cloud of plasma. The compound constitutes nearly half of the rocks' chemical makeup, according to the new study, which was published last week in the journal JGR Planets.