It was thought that the iron and magnesium-rich clay minerals in Gale Crater — which has also provided evidence of a long-term presence of liquid water in Mars’ past — would be a good place for organic matter to be preserved, as well.
But it turns out, according to a new study by a team of geoscientists at the University of Nevada Las Vegas, certain features of the clay minerals on Mars may not be conducive to the preservation of organic matter after all.
“We were able to show that the clay minerals formed from oxidized iron, rather than the reduced iron that had previously been thought,” lead author Elizabeth Hausrath said in an email to Seeker. “This suggests that if organic matter were present in the past on Mars, it might not be preserved to be detected today. So this might help explain why larger concentrations of organic matter haven't been detected on Mars, at least not yet!”
From previous experiments, it was thought that anoxic conditions — an environment without oxygen — were required for iron-magnesium clay minerals to form. On Earth, a hydrothermal vent would be an example of an anoxic environment. These vents are home to mostly microbes, and oxygen is actually toxic to most of them. Therefore, since thousands of locations on Mars have rock units containing iron-magnesium minerals it was thought any organics would be well preserved.
But Hausrath and colleagues were also able to synthesize clay minerals under oxidized conditions — where oxygen was present — which would destroy organic molecules. What they found is that these types of minerals actually formed faster when oxygen was present.
“The results suggested that the iron and magnesium-rich clay minerals formed quickly under oxidized conditions, which could help explain low concentrations of organics within some rocks or sediments on Mars,” former Ph.D. student Seth Gainey said in a statement.
Therefore, past organic matter, including possible signs of life, may not be well-preserved on Mars. But that doesn’t mean that life never formed on Mars. As we know on Earth, life seems to adapt to the conditions in which it was formed, and life on Mars may have perhaps developed to adapt to the oxidized conditions in the soil.
“Terrestrial life has certainly adapted to very challenging conditions,” Hausrath said. “For example, we have recently published work on how snow algae, which grow to very high concentrations in very challenging low nutrient snowy environments, are able to use minerals as nutrient sources. So certainly what we know of life from Earth is that it seems to be very able to adapt to challenging circumstances.”
The study Hausrath mention was published last month in the journal of the American Society for Microbiology. Her lab's latest findings were published in the journal Nature.
From all the evidence gathered by the Curiosity rover, scientists think Gale Crater was once the site of a lake billions of years ago, and rocks like mudstone formed from sediment in the lake. While organics were found there, there is not enough evidence to tell if the matter found by the rover team came from ancient Martian life or from a non-biological process. Some examples of non-biological sources include chemical reactions in water at ancient Martian hot springs or delivery of organic material to Mars by interplanetary dust or fragments of asteroids and comets.
But the discovery of organics shows that the ancient Martian environment offered a supply of organic molecules for use as building blocks for life and an energy source for life. Curiosity's earlier analysis of this same mudstone revealed that the environment offered water and chemical elements essential for life and a different chemical energy source.
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