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False biosignatures complicate search for earliest life

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From ScienceDaily:

The geological search for ancient life frequently zeroes in on fossilized organic structures or biominerals that can serve as “biosignatures,” that survive in the rock record over extremely long time scales. Mineral elements such as sulfur are often formed through biological activity. Microbes can also produce a variety of telltale extracellular structures that resemble sheaths and stalks.

However, according to new findings published in the journal Nature Communications, carbon-sulfur microstructures that would be recognized today by some experts as biomaterials are capable of self-assembling under certain conditions, even without direct biological activity. These “false” biosignatures could potentially be misinterpreted as signs of biological activity due to their strong resemblance to microbial structures.

“Surprisingly, we found that we could create all sorts of biogenic-like materials that have the right shape, structure and chemistry to match natural materials we assume are produced biologically,” said Associate Professor Alexis Templeton of CU Boulder’s Department of Geological Sciences and senior author of the new study. Paper. (public access) – Julie Cosmidis, Alexis S. Templeton. Self-assembly of biomorphic carbon/sulfur microstructures in sulfidic environments. Nature Communications, 2016; 7: 12812 DOI: 10.1038/ncomms12812 More.

Did you ever write away for a kit that promised you an underwater garden that was actually crystal salts building up? Really nice and very instructive, but not life.

See also: What we know and don’t know about the origin of life

and

What can we hope to learn about animal minds? (What makes it life?)

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One Reply to “False biosignatures complicate search for earliest life

  1. 1
    bornagain77 says:

    If false biochemical signatures were produced abiogenically by reacting sulfide with dissolved organics in special conditions, then the dissolved organic signature should easily have been picked up. Yet this signature hasn’t been detected:

    Evidence for life on Earth before 3,800 million years ago. Nature 384 – Mojzsis, S. J., Arrhenius, G. et al – December 1996
    Excerpt: The carbon in the carbonaceous inclusions is isotopically light, indicative of biological activity; no known abiotic process can explain the data. Unless some unknown abiotic process exists which is able both to create such isotopically light carbon and then selectively incorporate it into apatite grains, our results provide evidence for the emergence of life on Earth by at least 3,800 Myr before present.
    https://www.researchgate.net/publication/14307297_Mojzsis_S_J_Arrhenius_G_et_al_Evidence_for_life_on_Earth_before_3800_million_years_ago_Nature_384_55-59

    “We get that evidence from looking at carbon 12 to carbon 13 analysis. And it tells us that in Earth’s oldest (sedimentary) rock, which dates at 3.80 billion years ago, we find an abundance for the carbon signature of living systems. Namely, that life prefers carbon 12. And so if you see a higher ratio of carbon 12 to carbon 13 that means that carbon has been processed by life. And it is that kind of evidence that tells us that life has been abundant on earth as far back as 3.80 billion years ago (when water was first present on earth).,,, And that same carbon 12 to carbon 13 analysis tells us that planet earth, over it entire 4.5662 billion year history has never had prebiotics. Prebiotics would have a higher ratio of carbon 13 to carbon 12. All the carbonaceous material, we see in the entire geological record of the earth, has the signature of being post-biotic not pre-biotic. Which means planet earth never had a primordial soup. And the origin of life on earth took place in a geological instant” (as soon as it was possible for life to exist on earth).
    Dr. Hugh Ross – Origin Of Life Paradox (No prebiotic chemical signatures)- video (40:10 minute mark)
    https://www.youtube.com/watch?feature=player_detailpage&v=UPvO2EkiLls#t=2410

    As well, Evidence of photosynthesis is also implied by the oldest Banded Iron Formations (ca. 3.8 Byr-ago)

    Life’s history in iron – Nov. 7, 2014
    Excerpt: A new study examines how Earth’s oldest iron formations could have been formed before oxygenic photosynthesis played a role in oxidizing iron.,,,
    Microorganisms that photosynthesize in the absence of oxygen assimilate carbon by using iron oxide (Fe(II)) as an electron donor instead of water. While oxygenic photosynthesis produces oxygen in the atmosphere (in the form of dioxygen), anoxygenic photosynthesis adds an electron to Fe(II) to produce Fe(III).
    “In other words, they oxidize the iron,” explains Pecoits. “This finding is very important because it implies that this metabolism was already active back in the early Archean (ca. 3.8 Byr-ago).”
    http://phys.org/news/2014-11-l.....-iron.html

    Iron in Primeval Seas Rusted by Bacteria – Apr. 23, 2013
    Excerpt: The oldest known iron ores were deposited in the Precambrian period and are up to four billion years old (the Earth itself is estimated to be about 4.6 billion years old). ,,,
    This research not only provides the first clear evidence that microorganisms were directly involved in the deposition of Earth’s oldest iron formations; it also indicates that large populations of oxygen-producing cyanobacteria were at work in the shallow areas of the ancient oceans, while deeper water still reached by the light (the photic zone) tended to be populated by anoxyenic or micro-aerophilic iron-oxidizing bacteria which formed the iron deposits.,,,
    http://www.sciencedaily.com/re.....110750.htm

    As well, there is uranium/thorium fractionation which also gives us this biochemical signature for very early life:

    U-rich Archaean sea-floor sediments from Greenland – indications of +3700 Ma oxygenic photosynthesis (2003)
    http://adsabs.harvard.edu/abs/2004E&PSL.217..237R

    Thus, all in all, the biochemical signature evidence is robust in its indication of very early life on Earth:

    When Did Life First Appear on Earth? – Fazale Rana – December 2010
    Excerpt: The primary evidence for 3.8 billion-year-old life consists of carbonaceous deposits, such as graphite, found in rock formations in western Greenland. These deposits display an enrichment of the carbon-12 isotope. Other chemical signatures from these formations that have been interpreted as biological remnants include uranium/thorium fractionation and banded iron formations. Recently, a team from Australia argued that the dolomite in these formations also reflects biological activity, specifically that of sulfate-reducing bacteria.
    http://www.reasons.org/when-di.....pear-earth

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