Researchers from France, Spain and the United States have found evidence of clay minerals that suggests Mars may have been habitable once upon a time. The minerals were present in the clay samples the Curiosity rover had extracted from the Red Planet’s Gale crater in 2016. With support from the EU-funded MarsFirstWater project, the team analysed these samples and found them to be structurally and compositionally related to the glauconitic clays found on Earth. Their study was published in the journal ‘Nature Astronomy’. Previous investigations confirmed that a lake had existed in the 154-km-wide Gale crater for millions of years about 3.5 billion years ago. However, scientists weren’t sure if the body of water then had conditions such as low temperature and neutral pH needed to support life. The presence of glauconitic-like clays is a hopeful sign, since they indicate that liquid water may have been present for a long period of time under steady-state conditions.
What’s special about glauconite?
Glauconite is a greenish iron potassium phyllosilicate mineral mainly found in marine sediments, sandstones and carbonates. It needs stable conditions – namely temperatures between – 3 and 15 °C and water with a neutral pH – and many thousands of years to form. Its presence in the Gale crater clay samples therefore suggests that Mars at one time had the conditions to support its formation. The conditions required to form glauconitic clays in turn created the environment needed to host life millions of years ago. “Glauconitic clays can be used as ‘a proxy’ for stable conditions,” stated study lead author Elisabeth Losa-Adams of the University of Vigo, Spain, in an article posted on ‘New Scientist’. The research team used X-ray diffraction data obtained with Curiosity’s onboard instrument “to characterize the degree of disorder of clay minerals in the Murray formation at Gale crater,” the study reported. Next, they conducted geochemical modelling to see if the composition of the water in the Gale crater was consistent with the formation of glauconitic clay on Earth. They found that as water salinity increased due to evaporation, potassium levels in the water rose since the clay mineral nontronite doesn’t consume potassium. Then, as glauconite began to grow, potassium started to decrease since it was incorporated into the glauconite. Iron was initially incorporated into nontronite. “As glauconite and nontronite follow an opposite trend of dissolution and precipitation, the iron from nontronite is recycled. Consequently, the amount of iron in solution remains constant, increasing only at the end of the process and providing the source for further formation of oxyhydroxides,” the authors wrote. The researchers’ model captured the solvent-mediated transformation of nontronite into glauconite. “The conditions under which these minerals form are friendly for the presence of life,” observed Dr Losa-Adams in the ‘New Scientist’ article. However, the existence of conditions favourable for life isn’t evidence that life had actually existed on Mars. Having landed on the Red Planet in February 2021, NASA’s new rover Perseverance has been tasked with finding this evidence in the Jezero crater believed to be an ancient lake more than 3.5 billion years ago. As it investigates Mars’ aqueous environments, the MarsFirstWater (The physicochemical nature of water on early Mars) project may open new paths for the astrobiological exploration of the planet. For more information, please see: MarsFirstWater project web page
MarsFirstWater, Mars, water, Gale crater, Curiosity rover, clay, mineral, glauconite, glauconitic clay, nontronite