Mars explorers searching for signs of ancient life could be fooled by
fossil-like specimens created by chemical processes, research suggests.
Rocks on Mars may contain numerous types of non-biological deposits that
look similar to the kinds of fossils likely to be found if the planet ever
supported life, a study says.
Telling these false fossils apart from what could be evidence of ancient
life on the surface of Mars—which was temporarily habitable four billion
years ago—is key to the success of current and future missions, researchers
say.
Astrobiologists from the Universities of Edinburgh and Oxford reviewed
evidence of all known processes that could have created lifelike deposits in
rocks on Mars.
They identified dozens of processes—with many more likely still
undiscovered—that can produce structures that mimic those of microscopic,
simple lifeforms that may once have existed on Mars.
Among the lifelike specimens these processes can create are deposits that
look like bacterial cells and carbon-based molecules that closely resemble
the building blocks of all known life.
Because signs of life can be so closely mimicked by non-living processes,
the origins of any fossil-like specimens found on Mars are likely to be very
ambiguous, the team says.
They call for greater interdisciplinary research to shed more light on how
lifelike deposits could form on Mars, and thereby aid the search for
evidence of ancient life there and elsewhere in the solar system.
The research is published in the Journal of the Geological Society.
Dr. Sean McMahon, Chancellor's Fellow in Astrobiology at the University of
Edinburgh's School of Physic and Astronomy, said: "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. 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."
Julie Cosmidis, Associate Professor of Geobiology at the University of
Oxford, said: "We have been fooled by life-mimicking processes in the past.
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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