Mud cracks are evidence for sustained wet-dry cycles on ancient Mars, which might have provided conditions amenable to life (with caveats).

Mars panorama
This panorama captured by NASA’s Curiosity rover shows a location on Mars nicknamed “Pontours,” where scientists spotted preserved, ancient mud cracks believed to have formed during long cycles of wet and dry conditions over many years. Such cycles are thought to support conditions in which life could form.
NASA / JPL-Caltech / MSSS / IRAP

Planetary scientists analyzing data from the Curiosity rover have spotted the first evidence of wet-dry cycles on early Mars. Given that similar climatic cycles have long been linked to the advent of life on Earth, it could be an important step in understanding whether life-friendly conditions have ever existed on the Red Planet.

In a new paper released in Nature, a team led by William Rapin (University of Toulouse, France) describe mud cracks that Curiosity encountered back in 2021. “These particular mud cracks form when wet-dry conditions occur repeatedly — perhaps seasonally,” Rapin says.

The rover team found the cracks while ascending Mount Sharp, which towers 5 kilometers (3 miles) over Gale Crater. They encountered a rock nicknamed “Pontours” sandwiched between a clay-rich layer and another layer enriched with salty sulfates. Clay-rich layers tend to form in water, whereas salty layers emerge when water dries up.

As the Martian mud dried out, it shrank and fractured into T-shaped junctions. Repeating wet-dry cycles — perhaps as many as 10 — softened the junctions, changing them to Y-shaped. Where several Y-shaped junctions meet they create a distinctive patchwork of hexagonal cracks; this is what Curiosity saw. On average each hexagon is 4 centimeters (1.5 inches) across, although their diameters range from 1 cm to 7 cm.

Tracing mud cracks on Mars
A close-up of the panorama taken by Curiosity’s Mastcam at the “Pontours” rock reveals hexagonal patterns — outlined in red in the same image, right — that suggest the mud cracks formed after many wet-dry cycles occurring over years.
NASA / JPL-Caltech / MSSS / IRAP

While similar patterns can be found in Death Valley, California, tectonic activity on Earth has buried the evidence of more ancient cycles. “It’s pretty lucky for us to have a planet like Mars nearby that still holds a memory,” Rapin says. He and his team think that the Martian hexagons have been preserved for billions of years thanks to a salty crust that runs along the edges of the cracks. The cracks date to the Noachian–Hesperian transition, which occurred 3.8 to 3.6 billion years ago.

“This is the first tangible evidence we’ve seen that the ancient climate of Mars had such regular, Earth-like wet-dry cycles,” Rapin says. The pattern may have emerged as Gale Crater was repeatedly flooded or as ground water swelled upwards.

“We know that wet-dry cycles can drive chemical reactions to obtain the building blocks of life,” says Sidney Becker (Max Planck Institute of Molecular Physiology, Germany), who was not involved in the research. “Finding those conditions on Mars is an exciting discovery.”

As the water begins to dry up, it increases the concentration of soluble ingredients in the remaining water. This can boost chemical reaction rates and increase the chances of constructing the complex molecules that life relies on.

However, Becker also points out that wet-dry cycling isn't the only thing needed to assemble the building blocks of life — you also need the right atmospheric or mineral compositions. We don't yet know if Mars had those. And just because you have the building blocks doesn't mean they ever spark into life. “The conditions needed for the origin of life might be different to the ones that actually create the needed building blocks,” Becker says.

Even if the wet-dry cycles did help to create ancient life on Mars, they could also have worked against it. “The conditions to sustain life over a long period of time again could be very different,” Becker says. “Since first life was likely very fragile, wet-dry cycling might have caused too much external disturbance.” Life's maker could ultimately have been its destroyer.

So, while these cracks are an important piece of the Martian puzzle, we are still a long way from being able to say whether the conditions were right on ancient Mars for life to spark out of the mud.




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August 14, 2023 at 1:46 pm

"So, while these cracks are an important piece of the Martian puzzle, we are still a long way from being able to say whether the conditions were right on ancient Mars for life to spark out of the mud."

An interesting statement on the origin of life on Mars if it ever took place. I note here from Charles Darwin letters on the warm little pond scenario, 1871 and 1882.

My note Charles Darwin hoped that someday evidence would be shown for life evolving from non-living matter but in his time, none was known that was *worth anything* and the *law of continuity* would provide this, also a general law of nature for abiogenesis. None of this in science is proven at present let alone life evolving on Mars or living there in the present or past. There is no general law of abiogenesis seen operating in nature. So, here is a summary of four points in his letters that I learned. 1. A warm little pond is postulated for the origin of life on Earth but Charles Darwin thought if abiogenesis operating in a warm little pond in his time, perhaps such life evolving from non-living matter would be quickly destroyed by existing life and eaten. 2. No good evidence for abiogenesis taking place in Charles Darwin time seen in nature. 3. The law of continuity is needed for abiogenesis to work apparently, and 4. Someday a general law of nature developed to describe and show abiogenesis like other laws of nature, for example the laws of motion or law of gravity. Apparently all four I list here are missing in science today, even with natural law operating in nature in a uniform manner, i.e., *law of continuity*. When I consider point #1, it is good IMO to avoid catastrophism that wipes out abiogenesis creating life from non-living matter at the very beginning otherwise many abiogenesis events must be envisioned to replace the earlier efforts that failed. These are four points I learned by reading some of Charles Darwin letters on the warm little pond and origin of life on Earth.

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August 18, 2023 at 8:02 pm

After I studied Biology in the 1970s and read Stephen J. Gould's very Un-Darwin like descriptions of the fossil record I had serious doubts about 'smooth transitions' and like it or not Life was engineered. Using the building block metaphor they have never found a building block, which would be enzymes, proteins and complex polysaccharide carbohydrates. What they find are the sand and mud of a building block. Simple carbohydrates frozen in planetoids, has to be frozen to last because the same process that makes ribose, breaks it down within minutes. Racemic amino acids do not make a protein, only lefthanded (Hydrogen atom on the left) amino acids can make a protein and there are only 22 out of over 80 amino acids that are used in Life processes.

I see no processes that complicated so as to hook 150 lefthanded, electron spin down* amino acids to make a protein. Simpler forms? Name them.

*Recent discovery, Life just keeps getting more complicated the more we learn.

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August 24, 2023 at 12:17 pm

After reading Origin of Species, plus those letters you've mentioned, and I've come at the same four conclusions. What bothers me most is point number 4. We've physical there's for the formation and evolution of stars, galaxies, even the universe to some extent. Even if not all of them can be tested right away, nonetheless we still have theories. Albeit some wild ones. But regarding abiogenesis we have none. Following Carl Sagan, we are star stuff. On an atomic level, our bodies are made of the same elements that can found in the core of massive stars. So on an atomic scale we are just a sack of inert matter. All livings are. But we are a special sack. Our atoms, in fact, the atoms of the first primordial life forms, or perhaps, precursor molecules to primordial life arranged themselves in such a way that they essentially became living beings. But the question is how. Miller and Urey synthesized amino acids, the building blocks of life as I understand. I wonder what kind of synthesis, what parameters should must be set so that those amino acids assemble into something higher, something that resembles life. So I guess we need some law of rising complexity (I don't know if that makes any sense) which will tell us how to create life in a flask. Now this brings me to another question - can Darwin's evolution be applied to a larger scale - evolution starting at an atomic level, progressing to molecular level, origin of the first organisms, LUCA, and then the diversification we witness today. If we can figure out a physical theory of life, an equation giving us the blueprint of life, then we can answer questions about life's universality and the prevalence of life across the universe.

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Ted Kinyak

August 18, 2023 at 4:18 pm

So, these mud cracks could be billions of years old? I understand that there are no plate tectonics in effect, but is there no wind erosion? I know the atmosphere is much thinner on Mars but there is an atmosphere. I'm just surprised that even a thin atmosphere wouldn't have obliterated these marks after Billions-with-a-B years!

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