November 28, 2021

Beyond Going Long

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When searching for life on Mars, we must beware of ‘false evidence’

Fossil-like features we might find on Mars may have been formed in ways other than the activities of living things.

  • Current and planned missions to Mars are tasked with searching for evidence of extraterrestrial microbial life.
  • A couple of astrobiologists have warned that fossil-like structures can also be formed through non-biological processes.
  • Researchers have identified dozens of processes that make up similar features to the effects of microorganisms.
  • The authors of the new work therefore call for the need for comprehensive, interdisciplinary research that would determine how fake bio-fingerprints might appear on Mars.

If microbial life existed on Mars at least, thanks to tools like Perseverance in the roverAnd We have a good chance of finding traces of it in the form of microfossils – microfossils or biosignatures, that is, chemical traces resulting from the activities of living organisms.

But appearances can be deceiving. Structures that at first glance appear to be the fossilized remains of microorganisms or their activities can also be created exclusively through chemical processes. Therefore, we must be very careful when looking for the remains of life on Mars.

Astrobiologists have pointed to this possibility in a new review study, which published Scientific Journal The Scientific Journal of the Geological Society.

Exciting times for astrobiology

Humanity has never been closer to answering the question Whether life is on other planets as well.

Last year, the US National Aeronautics and Space Administration (NASA) sent the Persian squadron to the Mars rover, which landed on the surface of the Red Planet in February of this year, and is currently taking rock samples for analysis.

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The main task of perseverance is to find out whether there were conditions on Mars, at least in the past, suitable for the origin and development of life, and to find signs of its activity in the form of vital fingerprints.

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The European Space Agency (ESA) is working with the Russian space agency Roscosmos on another mission of similar focus – the ExoMars Mission. The Rosalind Franklin rover is scheduled to be sent to Mars next year.

Both rovers contain cameras and advanced multispectral instruments to analyze the rocks and organic matter they may contain.

We know what you’re looking for

Research on Earth’s biosphere and geological record has highlighted the enormous diversity of biosignatures that astrobiologists can discover on Mars.

These include, for example, fossils of various sizes, from the level of individual cells, through colonies, and biofilms to large structures such as Stromatolite. The presence of living organisms also refers to the finding of organic matter of composition and complexity that could only have been biologically formed.

Isotopic, geochemical or mineral anomalies, which on Earth can be interpreted as evidence of the activity of living organisms, are also possible indicators of the presence of life.

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Astrobiologists have collected countless such microbial biosignatures from environments with environmental conditions close to those on Mars in the distant past or even today.

Thus, scientists have a wide range of indications for the presence of life, which they can compare with their findings from Mars. Thus, the risk of reporting false positives is much lower today than it was during the Viking expeditions in the 1970s.

However, as astrobiologists from the University of Edinburgh and Oxford University point out, we still have to be very careful.

fake tracks

In the current study, the researchers point out the many errors in paleobiology and astrobiology that still occur today. For example, many presumed fossils are from the geological age Predcambrium, which was supposed to prove the existence of ancient life, was eventually proven to be the result of non-biological phenomena.

These were the so-called pseudofossils – structures that appeared at first glance as the remains or traces of living organisms, but were created by completely different “non-living” processes. At the same time, similar misinterpretations have occurred in the much newer layers of the fossil record.

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The famous electron microscope image shows the microscopic structures in the meteorite ALH84001, which was discovered in Antarctica in 1984. The remarkable formations resembling terrestrial bacteria were said to be the fossils of microorganisms on Mars.

Source: NASA

Probably the most famous mistake in astrobiological research occurred in 1996, when reports of microfossils were found in the Martian meteorite ALH84001. However, the initial enthusiasm soon faded.

Although the nature of these structures has not yet been clearly elucidated, experts have presented several options that could have arisen without the participation of organisms. Therefore, we no longer consider this meteorite reliable evidence of extraterrestrial life.

“In the past, we have been deceived by life-threatening processes. It has happened many times that bodies resembling fossil microbes have been described in ancient rocks on Earth and even in meteorites from Mars, but upon closer examination, they are found to be of non-biological origin.” remember Julie Cosmides, professor of geobiology and co-author of the study.

As these examples show, we must realize that even the return of samples and their subsequent analysis may not once and for all answer the question of whether there was or at least ever existed on the Red Planet. Although we hope for clear evidence, the true origin of potential biometric fingerprints may be somewhat uncertain.

“This article is intended as a warning that we call for further research into simulations of life in the context of Mars, in order to avoid repeating previous mistakes,” Cosmides says.

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Long but necessary list

British astrobiologists have compiled a list of all the possible processes that could create supposed traces of organisms in the rocks of Mars. They identified dozens of diverse phenomena that produce structures that mimic the fossils of microorganisms.

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Processes of a purely chemical nature can produce formations that are clearly deposited on the fossilized cells of microorganisms such as bacteria. Another example is the so-called chemical gardens – plant-like structures formed by reactions between salts transitional elements and aqueous silicate solutions.

Many of these chemical reactions occur in the presence of liquid water, one of the necessary conditions for the origin and development of life as we know it.

Vital minerals can also be deceptive – that is, minerals whose composition has been adapted by living organisms. They are very common on our planet – practically all groups of living things can create them. For example, we can mention silicates, carbonates or phosphates, which are the main component of the chests and bones of animals.

Biogenic minerals have properties that make it possible to distinguish them from minerals formed without the participation of living organisms. However, a wide variety of non-living processes can form minerals of similar shape and texture to bio-minerals.

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Therefore, the form alone is not sufficient to unambiguously determine the organic origin of the mineral. In that spirit, we can move forward.

“At some point, a Martian spacecraft will find something that looks like a fossil, so our ability to distinguish it from structures and materials from chemical reactions is very important,” said astrobiologist and first author Sean McMahon.

So the authors call for more rigorous research and interdisciplinary collaboration so we know how formations that mimic the effects of life form on the Red Planet.

“There is at least one non-biological process for each fossil type that is very similar, so we really need to improve our knowledge of how they formed,” McMahon adds.