On Earth, we all know what alters our landscapes: water erosion, winds, tectonic activity, and volcanoes. Today on Mars, wind erosion is difficult. The wind is a ruthless sculptor everywhere. It may have created places where planetary scientists and astrobiologists search for traces of primitive Martian life today.
The work of the winds of Mars
Since Mars has lost its water, the gentle force of wind erosion has altered the surface of Mars and affected the geology of Mars. That’s the conclusion of a group of planetary scientists led by astronaut and planetary scientist Jessica Watkins and Caltech professor John Grotzinger. Watkins worked as a postdoc with Grotzinger and is the first author of a research paper describing their team’s work. (As it turns out, I checked the final version of the paper while on the International Space Station.)
“This paper describes the discovery of mismatches in a series of sedimentary rocks on Mars,” she said, describing a discontinuity, or discontinuity, in the time of deposition between rock chains. “In this case, it separates the rocks that record the time the lake was in Gale Crater and the rock sequences above it that records a time when the climate was drier resulting in the formation of the Aeolian sand dunes. The mismatch is important because it does not record the transition between ecosystems. Not only does it record significant erosion of older rocks (lactrin or lake) before deposition of younger rocks (eolian or wind-driven).”
Watkins began studying Earth forms and processes here on Earth as a way of understanding the same events on Mars. “Mars is like Earth in many ways,” she said. “I found it fascinating that we could study Earth processes and formations to better understand those observed on Mars (and vice versa!). Her work on atmospheric (wind-driven) processes on Mars led to a close examination of Curiosity’s findings.
A look at the Martian rock cycle
Grotzinger was the project scientist on the Curiosity mission. This rover still provides direct evidence that geology on Mars is very different from that on Earth. “The action of erosion on Mars is primarily driven by winds that act like a feather duster over hundreds of millions to billions of years,” Grotzinger said. “This is very different from, say, land, where the severe ruggedness of the San Gabriel Mountains is created by torrents of rainwater that dissects the landscape over relatively brief periods of geological time.”
While one of the goals of Mars missions is to “find water,” understanding the rock cycle is critical. Planetary scientists wonder, how did the layers of Martian rocks form? How do they change? What destroys them? On Earth, molten rock from volcanic features flows out to form igneous layers. It is eroded by wind and rain and accumulates in the form of sedimentary rocks. Water movement is a big player here, as well as wind-blown sand and rock deposits.
Finally, tectonic activity from below pushes rock layers upward (or brings them down). Tectonic plates can slide over each other, causing continents to break up or collide. This process led to the building of the Himalayas and helped raise the Rocky Mountains. After that, erosion takes control and moves rock chunks around.
Mars doesn’t have that kind of activity these days. Of course, it had active volcanoes, flooding the earth with lava. Just take a look at the Tharsis Bulge to see how the lava buildup affected that area. We all know that Mars has water. There is evidence of this all over the planet. But, there are no tectonic plates that slide and slide around causing Martian earthquakes and surface-changing spells. So, without flowing water causing erosion over the past few billion years, what else would change the landscape of Mars? The answer seems to be: wind erosion.
Clues from the wind
Now, you might think that there isn’t enough atmospheric pressure or volume on Mars to cause gale-force eroding winds. Well, that’s kind of true. But the effect of wind erosion is present. You just have to look for it carefully. This is what Watkins, Grotzinger and their colleagues did. They studied Curiosity’s observations in Gale Crater for clues.
Gale Crater is a dry lake bed 60 km in diameter on the surface of Mars. While moving through the crater, the Curiosity rover tracked Murray formation. This is a layer of mudstone 300 meters thick named after the late Bruce Murray. He was a California Institute of Technology professor of planetary sciences and past head of the Jet Propulsion Laboratory. Clay stone consists of fine-grained clay pressed by layers on top of it. Some of the upper layers are relatively immune to wind erosion. However, in other places, the wind eats the upper layers. There are also areas that look like ancient sand dunes that run throughout the area. As they moved, they deposited layers of sand, propelled by the wind.
“Gale Crater is a great place where you can document multiple cycles of erosion,” Grotzinger said. “All of this helps us understand how Mars works in general and will inform scientists interpreting the rover’s persistent observations as well.”
Wind erosion, sedimentary rock and life
So, it looks like wind erosion — even the gentler style we see on Mars, can make big changes at the surface there. When water exposes layers of rock on Earth, wind does so on Mars. The results of natural changes caused by erosion at Gale Crater could be evidence of similar changes elsewhere on Mars. Data from Curiosity and Perseverance are giving planetary scientists like astronauts Watkins and Grotzinger new insight into the processes that shape rocky surfaces, and possibly – preserving evidence of ancient life.
On Earth, wind erosion and deposition of sand and rock particles have preserved examples of our primitive biosphere. If the same thing happened to any possible early life on Mars, the wind-blown sedimentary rocks on the Red Planet could be a treasury of Mars’ vital fingerprints.
In a Q&A with students in August 2022, astronaut Watkins reported on current persistence mission studies of eroded sediments in ancient lake bed deltas. I am so excited about the delta deposits that the perseverance is starting to climb.” “I think it will be really enlightening for us and hopefully give us insight into the habitability of Mars and hopefully find signs of ancient life as well. These delta deposits would be the perfect place, if there were those marks in there, that’s where they would be.”
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