Hunting for Martians may be a tougher task than predicted. Clays, long thought to be a sure sign of a warmer and wetter past on the Red Planet, could merely signal earlier volcanic activity – which would have made some regions on Mars less favourable for life.
Clay layers found across Mars suggest that during the Noachian period, from about 4.2 billion to 3.5 billion years ago, the planet was warm enough to host liquid water – necessary for life as we know it.
Scientists thought Mars clays could have formed in one of two ways: through soil interacting with standing water on the surface, or from water bubbling up from below via hydrothermal vents.
"Both of those would have created habitats that would have supported microbes," says study co-author Bethany Ehlmann of the California Institute of Technology in Pasadena. "On Earth, microbes would have been thriving away, enjoying themselves."
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