Scientists should remain skeptical if they study rock samples drilled by NASA’s Perseverance rover for evidence of alien life lest they be fooled by fake fossils, academics in the UK have warned.
It’s difficult to find definitive signs of ancient microbial life in geological materials, Sean McMahon, an astrobiologist at the University of Edinburgh, and Julie Cosmidis, a geobiologist from the University of Oxford, argued. Chemical processes on the Martian surface could produce substances very similar to those created by living organisms.
Interesting patterns in sediments of clay or layers of rock may look as if they were deposited by cellular life, such as stromatolites, for example. Scientists may be excited about finding these structures, but before they jump the gun they should also consider whether those markings may have been carved by geological or chemical processes on Mars.
For every type of fossil out there, there is at least one non-biological process that creates very similar things, so there is a real need to improve our understanding of how these form
“At some stage a Mars rover will almost certainly find something that looks a lot like a fossil, so being able to confidently distinguish these from structures and substances made by chemical reactions is vital,” McMahon, also a chancellor’s fellow in the school of physics and astronomy at Edinburgh, said on Wednesday.
“For every type of fossil out there, there is at least one non-biological process that creates very similar things, so there is a real need to improve our understanding of how these form.”
The trouble is scientists don’t know enough about these processes to rule them out. “These phenomena tend to be driven by kinetic processes far from thermodynamic equilibrium, often in the presence of liquid water and organic matter, conditions similar to those that can actually give rise to, and support, life,” the pair wrote in a paper published in the Journal of the Geological Society.
Boffins have been duped by fake fossils in the past. In the nineteenth century, paleontologists thought they had discovered the oldest fossil in the world. The specimen, known as Eozoon canadense, or the "dawn animal of Canada," was made up of crystalline calcite and serpentine organised into a wavy pattern like ripples in a pond. At the time, eggheads thought they had stumbled across a massive imprint of a single-celled organism known as Foraminifera.
But decades later, the sample was labelled as a psuedo-fossil after scientists discovered non-biological explanations for the patterned rock. Similar scenarios of strange marks that look like worm tracks or arthropods have fooled people before.
A meteorite example from Mars, codenamed ALH84001, made headlines after it was studied in 1996, for containing what appeared to be a morphological fossil. Clusters of nodules made out of carbonate and magnetite excited experts, who believed they were made from bacteria. Although it's still not clear how these structure formed, scientists no longer consider ALH84001 a serious candidate of evidence for alien life on Mars.
“We have been fooled by life-mimicking processes in the past,” Cosmidis, an associate professor at the department of earth sciences at Oxford, said.
“On many occasions, objects that looked like fossil microbes were described in ancient rocks on Earth and even in meteorites from Mars, but after deeper examination they turned out to have non-biological origins. This article is a cautionary tale in which we call for further research on life-mimicking processes in the context of Mars, so that we avoid falling into the same traps over and over again.”
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Instead, Cosmidis and McMahon believe astrobiologists should systematically look for more possible non-biological pathways that create false biosignatures in the lab to prepare for the Perseverance’s future return mission.
"If we are lucky, plain and unequivocal biosignatures will be discovered on Mars in the coming decades. But in light of the many cautionary tales in the history of palaeontology and astrobiology, it seems prudent to anticipate more ambiguous results," they concluded.
"Further work on the physics and chemistry of far-from-equilibrium systems will ultimately reveal the limits of abiotic self-organization and may even lead to new discoveries on the organizing principles at the origin of life on Earth. Such efforts have an important part to play in the interpretation of Earth's rock record as well as the search for life on Mars and elsewhere in the Solar System." ®