Clay layers on Mars may have harbored ancient life

Thick, planet-wide blankets of clay are among the Red Planet’s most intriguing geological puzzles. Because clay forms only in the presence of abundant liquid water, scientists have long viewed these deposits as potential time capsules for ancient life.

A new study now paints a clearer picture of where, when, and how those mineral layers took shape.

Led by planetary geologist Rhianna Moore during her postdoctoral work at The University of Texas at Austin, the team sifted through high-resolution images and topographic data for 150 previously cataloged clay outcrops.

Quiet clay terraces on Mars

Thick clay deposits span across Mars and consistently show a surprising set of shared traits. Most sit at low elevations, adjacent to the vestiges of long-vanished lakes. Yet they remain distinctly removed from ancient river valleys that once carved the highlands.

“These areas have a lot of water but not a lot of topographic uplift, so they’re very stable,” Moore said. She added that such stability would have limited destructive erosion by fast-moving water.

This would have allowed clays to accumulate layer upon layer rather than being scoured away.

“If you have stable terrain, you’re not messing up your potentially habitable environments. Favorable conditions might be able to be sustained for longer periods of time,” she said.

Lessons From Earth’s tropics

Study co-author Tim Goudge, an assistant professor in UT Austin’s Department of Earth and Planetary Sciences, sees an echo of earthly analogues in Mars’ ancient past.

“On Earth, the places where we tend to see the thickest clay mineral sequences are in humid environments, and those with minimal physical erosion that can strip away newly created weathering products,” said Goudge.

The Martian patterns, he noted, match the latter half of that recipe almost perfectly. “These results suggest the latter element is true also on Mars, while there are hints at the former as well.”

Because Mars lacks plate tectonics, its surface doesn’t undergo the constant stirring seen on Earth.

That relative stillness, combined with a clement climate billions of years ago, created quiet basins where rainfall and standing ponds could slowly break down volcanic rock into clay minerals. Violent floods didn’t sweep the new sediments away, allowing them to accumulate over time.

A carbonate conundrum

The same conditions that favored clay formation could also explain one of Mars’ long-standing mysteries: the scarcity of carbonate rocks.

On Earth, volcanic CO2 reacts with fresh basaltic crust, eventually locking carbon into sprawling beds of limestone and dolomite. But on Mars, with no tectonic conveyor belt to bring up fresh lava, that cycle stalled.

Instead, the study proposes, CO2 may have remained aloft longer, warming the planet and further fueling slow, persistent weathering that built clays.

At the same time, by trapping byproducts of that weathering inside impermeable mineral layers, clay growth might have robbed the environment of ingredients needed to form carbonates in the first place.

“It’s probably one of many factors contributing to this weird lack of predicted carbonates on Mars,” Moore said.

Signs of life-friendly conditions

Taken together, the findings hint at expansive, placid watery habitats that persisted long enough to concentrate minerals – and perhaps organic molecules – essential for life.

Thick clays help astrobiologists by preserving biochemical evidence, protecting it from radiation and geological disruption.

Moore, now part of NASA’s Artemis program team, emphasized that the work grew out of UT Austin’s Center for Planetary Systems Habitability, an initiative that crosses disciplinary boundaries to answer where life might arise beyond Earth.

By mapping mild, lake-adjacent clay basins, the study offers a shortlist of enticing targets for future rover missions or even human explorers looking for fossilized biosignatures.

Conditions where life may have thrived

Mars today is frigid and desiccated, but during the period when these clays formed – more than three billion years ago – it was likely dotted with lakes and seas.

The new analysis suggests those bodies of water were not just transient puddles fed by catastrophic floods. Instead, long-lived, shallow basins may have hosted slow-unfolding chemical reactions over millennia.

Although valley networks delivered water downhill, the most extensive clay blankets on Mars avoided the valleys themselves. This is evidence that turbulence and sediment-choked streams were not the primary architects.

Instead, chemical dissolution – not physical abrasion – sculpted much of the ancient surface. That balance created calm, warm conditions where life might have thrived beneath a thicker, greenhouse-gas-rich atmosphere.

Probing clays for clues

With orbiters continuing to beam back ever finer data, researchers hope to refine models of how water cycled through early Mars. Drill cores from future missions could verify the age, chemistry, and longevity of the newly mapped clay fields.

Meanwhile, laboratories on Earth will experiment with simulated Martian conditions to test whether stable, low-energy ponds truly can yield the mineral fingerprints observed from space.

For now, the study suggests that Mars’ most promising habitats might not have been in raging river deltas. Instead, they may have been in quiet lakeshores where mud settled gently, season after season, sealing away the planet’s watery secrets – and perhaps its biological ones as well.

The study is published in the journal Nature Astronomy.

Image Credit: Credit: NASA/JPL-Caltech/UArizona

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