3.5 billion years, the evolution of life on Mars: it is very likely that it will not exceed the single-cell stage!

[Mobile software: Bo Ke Yuan] Undulating land streaks can be seen from space, revealing that rivers once flowed across the surface of Mars, but how long did the water flow on Mars? According to a new study from Stanford University, there was enough time to record evidence of ancient life on Mars. Scientists speculate that Jezero Crater on Mars, the site of NASA's next Mars rover to the red planet, may be a good place to look for signs of life, and a new analysis of satellite images supports this hypothesis.

By simulating the length of time it would take for sediment layers to be deposited in deltas as ancient Martian rivers poured into craters, scientists concluded that if life ever existed near the Martian surface, traces of that life might be captured in the delta layers. Lead author Mathieu Laptre, an assistant professor of geological sciences at Stanford University's School of Earth, Energy & Environmental Sciences (Stanford Earth), said: "Water existed on Mars for a long time, and the environment there was likely habitable, even if it might have been arid."

Image: NASA's Mars 2020 Perseverance rover, expected to launch in July 2020, will land in Jezero Crater, as shown here. The image was taken by an instrument on NASA's Mars Reconnaissance Orbiter, which regularly captures potential landing sites for future missions.

The study found that the sediments were deposited quickly, and if there were organics, they would have been buried quickly, meaning they would have likely been preserved and protected. Jezero Crater was chosen for NASA's next Mars rover mission in part because the site contains a river delta, which on Earth is thought to effectively preserve organic molecules associated with life. But without knowing how quickly the delta formed and how long it lasted, the analogy remains speculative, said the study published in the journal AGU Advances.

Extrapolation from Earth

The study provides guidance for Mars sample return to better understand the ancient climate of Mars and the duration of delta formation for NASA's Perseverance rover to Mars. It is expected to launch in July 2020 as part of the first Mars sample return mission. The study incorporates a discovery scientists made on Earth: single-line meandering rivers without plant growth on the banks move sideways about 10 times faster than rivers with vegetation. Based on the strength of Mars' gravity and assuming that there are no plants on the Red Planet, scientists estimate that the delta in Jezero crater took at least 20 to 40 years to form.

Image: Scientists believe a meandering river without vegetation in the center of the McLeod Springs Wash in the Toiyabe Basin of Nevada is similar to the stream in the ancient Jezero Crater on Mars.

But the formation was likely discontinuous, perhaps spread out over a period of about 400,000 years. That's useful because one of the biggest unknowns on Mars is time, and by finding a way to calculate the rates of flow, the researchers can start to get that time dimension. Because single-line, meandering rivers are most commonly found under vegetation on Earth, their appearance went largely unnoticed until relatively recently. Scientists thought that before plants appeared, only braided rivers, made up of multiple, interlaced channels, existed.

Image: NASA's Perseverance rover operating on the surface of Mars.

Now that researchers know to look for them, scientists have found meandering rivers on Earth today where there are no plants, such as McLeod Springs Wash in the Toyabe Basin in Nevada. This is something no one has studied before because single-line rivers without plants don't really show up on the radar. It also has cool implications for how rivers on Earth may have run before there were plants. The researchers also estimate that wet periods that favored significant delta buildup were about 20 times more frequent on ancient Mars than on Earth today.

Possible evolution of life on Mars

Now, scientists are increasingly thinking about the fact that water flow on Mars may not be continuous, with some days of flow and other days of drought. This is a novel way to put quantitative constraints on how often flow may have occurred on Mars. The findings from Jezero Crater may help us understand how life on Earth evolved. If life once existed in Jezero Crater on Mars, it likely did not evolve beyond the single-cell stage. This is because Jezero Crater was formed more than 3.5 billion years ago, long before organisms on Earth became multicellular.

If life once existed on the surface of Mars, its evolution was stalled by some unknown event that sterilized the planet. This means that Martian craters could serve as a kind of time capsule, preserving signs of life as it once might have existed on Earth. The ability for scientists to use another planet as a laboratory experiment to study how life might have started elsewhere, or better yet, to document how life began, could actually teach us a lot about what life is. These will be the first rock samples that humans have ever seen on Mars and brought back to Earth, so it's pretty exciting.

Boco Park | Research/From: Stanford University

Reference journal: AGU Advance

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