The ongoing search for life on other planets hinges on finding traces of water. However, a new study about how organisms on Earth fail to thrive even in watery conditions offers a cautionary tale on this approach.
For their research into the extreme limits of life’s survival, scientists traveled to the Dallol hydrothermal pools of northern Ethiopia, near the Eritrean border.
“We identify two major physicochemical barriers that prevent life from thriving in the presence of liquid water on Earth and, potentially, elsewhere, despite the presence of liquid water at the surface of a planet being a widely accepted criterion for habitability,” the researchers write.
The Diversity, Ecology and Evolution of Microbes (DEEM) team of biologists from French national research agency CNRS and the University of Paris-Sud visited the Dallol area several times between 2016 and 2018. After deploying a range of scientific techniques to search for any trace of life, they ultimately concluded that the combination of extreme levels of saline and acid were too much for any organism, however hardy or small.
An earlier recent study of this incredibly inhospitable area claimed to have uncovered some evidence of extremely tiny microbial life surviving against all the odds. However, this has been disputed by the researchers behind the latest paper on the topic.
Last summer, months before publishing their findings in greater detail, the DEEM team tweeted that though they’d found some contaminants, there is no life inside the hyperacidic and hypersaline pools.
The contaminants included some known molecular biology kit and lab contaminants, as well as bacteria likely introduced by human tourists to the site. The team also noted they’d found extremely small particles of silica that resemble tiny cells and which could be misinterpreted as signs of life.
The findings were not completely pessimistic about the chances for life to find a way in harsh conditions: an array of single-celled microorganisms known as ‘archaea’ were found living in some of the less extreme pools.
The team hopes that their findings, which have been published in Nature Ecology & Evolution, help by restricting the presumed parameters for habitability, but should also be heeded as something of a warning about how scientists interpret biosignatures “on Earth and beyond.”
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