Hexagonal cracks in mud that form when Mars cycles from wet to dry have been found in sedimentary rock samples dating back 3.6 billion years. There are seasons on Mars. Moisture and rain must be repeated periodically for life to emerge./NASA/JPL-Caltech
It was found like a geological fossil that shows that there were seasons on Mars as well. It is a trace of cracks in the shape of a hexagon as the mud dried 3.8 billion years ago. This shape was evaluated as confirming the environment in which life could have been born on early Mars in that it was possible when the dry and rainy seasons were repeated like Earth.
William Rapin, a planetary scientist at the French Institute of Astrophysics and Planetology, said in the international journal Nature on the 10th, “NASA’s Curiosity rover has discovered a 3.6 billion-year-old sedimentary layer in the Gale crater on Mars. Hexagonal-shaped salt deposits were found in
The hexagon discovered this time is the first fossil evidence showing that the dry and rainy seasons periodically repeated on Mars, the researchers explained. Other studies have previously shown that molecules must interact repeatedly at different concentrations to create essential substances for life. The research team said that the hexagonal geologic fossil shows an environment essential for the birth of life on Mars in that such a change in concentration is possible only when the dry and rainy seasons are repeated.
Hexagonal fossil morphology of sedimentary rocks analyzed by Curiosity on the 3154th day after passing through the Gale crater on Mars./NASA/JPL-Caltech/MSSS/IRAP
◇Hexagonal cracks are created by repeating wet and rainy seasons
The Curiosity rover climbed the 5km-high Mount Sharp from the Gale crater in 2021. The rover found mud cracks in samples taken from a rock dubbed ‘Pontours’ between the clay layer and the sulfate-rich layer above it. The width of each hexagon was 4 cm. The water depth at the time was estimated to be 2 cm.
Clay usually forms in water, but sulfates form as the water dries. Hexagonal cracks mean that they were formed when water filled and then dried. Curiosity’s precision laser instrument, ChemCam, identified hard sulfate layers at the cracked edges of the mud. The saline layer became a kind of protective layer, allowing the mud cracks to be preserved for billions of years, the researchers explained.
Scientists investigate the geology of Mars because it itself is a fossil that shows the past history. Earth is constantly changing as tectonic plates collide with each other, but Mars has no such plate structure, so it retains its appearance billions of years ago. In the 1990s, Mars-orbiting NASA probes captured for the first time dried-up rivers, canyons, deltas, and sedimentary layers on Mars. This is evidence that liquid water flowed on Mars in the past, raising expectations for the discovery of life.
“The geological features of the surface suggest that the ancient Mars climate was much warmer and wetter than it is today,” said Dr. Ashwin Vasavada of NASA’s Jet Propulsion Laboratory’s Curiosity Rover Project. In 2012, Curiosity first discovered simple organic molecules that could be formed by both geological and biological processes on Mars.
The question is whether warm, humid conditions on early Mars could have persisted long enough for life to emerge. Today, Mars has almost no atmosphere, so water is presumed to be trapped in frozen ice caps or minerals in the crust. Billions of years ago, when solar energy was much weaker, things would have been much worse.
Some scientists claim that volcanic eruptions or asteroid impacts sometimes injected greenhouse gases into the Martian atmosphere, briefly warming the otherwise cold and dry climate. On the other hand, other researchers believe that the geology of Mars suggests that a warm and humid climate continued to exist in the past. The Curiosity rover this time found hexagonal cracks in ancient rocks on Mars, reinforcing the argument that a warm climate lasted. Even in places such as Death Valley in the Mojave Desert Valley in the United States, these cracks form after years of repeated wet and dry seasons.
Mars panorama taken by NASA’s Curiosity rover. This time, they discovered an ancient mud crack that is believed to have formed during repeated wet and dry conditions./NASA/JPL-Caltech/MSSS/IRAP
◇Dry air is essential for the formation of biomolecules such as genetic material
Dr Raffin explained that when the Martian mud first cracked as it dried, it was square with sharp T-shaped angles. Then, whenever the mud was filled with water again, the cracks would stick together little by little and open again when the ground dried again. Over time, the crack’s sharp angle softens into a Y-shape, creating the hexagonal shape discovered this time, Dr. Raffin said. “It is impossible to create a hexagonal shape without repeating wet and dry cycles,” said Dr. Raffin.
The cycle of repeating dry and rainy seasons according to the season is an ideal condition for the birth of life. Life tends to use long chains of carbon molecules called polymers. All molecules essential to life, such as amino acids that make up proteins and nucleic acids (nucleotides) that make up DNA, are in that form.
Water is essential to form polymer chains. This is because the constituents must dissolve in water. However, there should be neither too much nor too little water. Too much water prevents the molecular components from sticking together. The wet-dry cycle controls the concentration of materials that feed the chemical reactions that lead to polymer formation.
Past experiments have shown that chemical reactions such as polymerization and condensation that build biomolecules often require periods of dehydration without water. Professor Mark Sephton of Imperial College in the UK told New Scientist that “there is a raw soup, and when it is dried, it has the potential to stick together unless it is broken down by radiation or oxidation.” Dr. Nina Lanza of the Los Alamos National Laboratory in the United States, a co-author of this paper, said, “The dry-wet cycle that balances the two conditions is key to the birth and survival of life.”
Despite this discovery, many questions remain unanswered. “This discovery has raised more questions than answers,” said Edwin Kite, a professor at the University of Chicago. .
Dr. Raffin believes that ancient rocks on Mars provide evidence of Earth’s early lost planetary state. This could be the key to unraveling Earth’s past. Just as Earth’s Death Valley helped analyze mud cracks on Mars, future knowledge from Mars will help us understand how life began on Earth, the researchers said.
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