Potential Biosignatures on Mars May Reflect Ancient Life in Mineral-Rich Rocks

Potential biosignatures on Mars, embedded within ancient rocks, have opened up a exciting new lead in the search for signs of Marian life. While surveying a set of outcrops near a dried-up river valley on the Red Planet, NASA’s Perseverance came across something exceptional: a series of irregular marks displayed in layers of fine-grained mudstones. Research is now suggesting that these features may have been created by microbial life billions of years ago.

The study, published in Nature, explains how chemical processes spurred by microbial life could have potentially left the peculiar mudstone features. The presence of organic carbon alongside two iron-rich minerals that are often linked with microbial life on Earth reinforces this idea, yet researchers still have years of work — and waiting — ahead of them to determine whether this discovery truly represents a legitimate sign of ancient life on Mars.

Exploring an Ancient River Valley

Ever since the Perseverance rover landed at Jezero Crater on Mars in 2021, it has been traversing all across a landscape where water was plentiful 3.5 billion years ago. During this time, active rivers transported mud, sand, and gravel to a lake that filled Jezero Crater. In the calmer periods that followed, this sediment settled and eventually formed rocks, like rust-colored mudstones made of silt and clay.

As Perseverance explored through the Neretva Vallis river channel, it directed its attention to the Bright Angel formation, a set of outcrops that appeared after the lakes and rivers dried up. In July 2024, the rover collected a sample core from a rock called “Cheyava Falls” at the northern edge of this region. The mudstone here was found to contain two noteworthy features that the researchers refer to as “poppy seeds” — dark specks in the rock — and “leopard spots” — ring-shaped masses with dark rims.

Read More: Mars’ Liquid Core May Have Once Powered Only Half of its Magnetic Field

Signs of Microbial Activity

The irregular shapes and spacing of these features told researchers that they weren’t deposited as grains, but instead were byproducts of “redox reactions,” chemical processes that involve the transfer of electrons.

Digging further into this oddity, the rover used its SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instrument to detect signatures of organic carbon in Cheyava Falls and several other rocks.

Then, with its PIXL (Planetary Instrument for X-Ray Lithochemistry) spectrometer, it was able to see minerals all throughout Cheyava Falls. The rover observed some areas enriched in iron and phosphorus (in the poppy seeds and rims of leopard spots) and others enriched in iron and sulfur (in the cores of leopard spots). The researchers believe that the iron phosphate represents the mineral vivianite and the iron sulfide represents the mineral greigite.

The reason why these minerals are so significant is that in sediments on Earth, they’re usually produced by microbes that consume organic matter. The combination of organic matter and the minerals in Cheyava Falls, then, suggests that there’s a chance microbial life was once doing something similar on Mars.

“It’s not just the minerals, it’s how they are arranged in these structures that suggests that they formed through the redox cycling of iron and sulfur,” said co-author Michael Tice, a geologist at Texas A&M University, in a statement. “On Earth, things like these sometimes form in sediments where microbes are eating organic matter and ‘breathing’ rust and sulfate. Their presence on Mars raises the question: could similar processes have occurred there?”

Waiting on Answers

Even though Cheyava Falls presents compelling evidence, it doesn’t necessarily confirm the existence of life on Mars. That’s why this discovery is only referred to as a “potential biosignature,” which is defined as “a substance or structure that might have a biological origin but requires more data or further study before reaching a conclusion about the absence of presence of life.”

Technically, vivianite and greigite can emerge without the presence of life, through geochemical processes; one example involves sustained high temperatures. However, the researchers say that their examination strongly indicates that the rocks were never heated in a way that would produce the poppy seeds and leopard spots.

The newfound biosignatures could mean that microbes were on Mars at the same time life was just starting to arise on Earth. But researchers won’t know for sure until more studies are conducted, and it may be a while before the Cheyava Falls sample is brought to Earth. NASA and the European Space Agency are collaborating on plans for a Mars sample return mission, but so far, they’re still in the design stages. Scientists may not get a better look at the sample until around 2030 or beyond.

Read More: There Is More Evidence of an Ancient Lake with Flowing Rivers on Mars

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