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| Image Credit: Helge Mißbach |
Organic
molecules preserved in remarkably ancient rock formations in Australia have
been found by researchers, exposing what they claim is the first detailed
evidence of early chemical ingredients that may have underpinned the primordial
microbial life-forms of Earth.
The find,
made in Western Australia's Pilbara Craton's 3.5 billion-year-old Dresser
Formation, adds to a large body of research pointing to ancient life in this
part of the world, marking one of only two pristine, uncovered land deposits on
Earth dating back to the Archean Eon.
In recent
years, with scientists finding "definitive evidence" of microbial bio
signatures dating back to 3.5 billion years ago, the hydrothermal rock of the
Dresser Formation has thrown up repeated signs of what looks to be the earliest
known life on earth.
In a new
study, researchers in Germany have now found traces of unique chemistry that
may have made it possible for such primordial species to exist, and have
identified biologically important organic molecules contained within barite deposits,
a mineral produced by different processes, including hydrothermal phenomena.
Barites
are directly associated with fossilized microbial mats in the area, and when
freshly disturbed, they smell like rotten eggs, explains geobiologist Helge
Mißbach of the University of Cologne, Germany.
We
therefore hypothesized that they contained organic material that for early
microbial life may have served as nutrients.
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| Barite rock from the Formation of Dresser. (Mißbach's Helge) |
While
researchers have long speculated how organic molecules can serve as substrates
for primitive microbes and their metabolic processes, direct evidence has
proven to be largely elusive to date.
To
investigate, Mißbach and fellow researchers investigated inclusions from the
Dresser Formation inside barites, with the chemically stable mineral able for
billions of years to retain fluids and gases within the rock.
The
researchers found what they classify as an intriguing diversity of organic
molecules with established or inferred metabolic significance using a variety
of techniques to examine the barite samples, including gas chromatography-mass
spectrometry, micro thermometry, and stable isotope analysis.
In
addition to various gases, including hydrogen sulfide that may have had biotic
or abiotic origins, the organic compounds acetic acid and methane thiol were
among these.
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| Image Credit: Helge Mißbach |
ABOVE:The Barite rock, which suggests a close link with stromatolites.
The near
proximity of these inclusions inside the barite rock and adjacent organic
accretions called stromatolites, although it may be difficult to be sure of the
exact links, indicates that the ancient chemicals, once held within
hydrothermal fluids, may have affected primitive microbial communities.
Indeed, in
the barite-hosted fluid inclusions, several compounds found... would have
provided ideal substrates for the previously proposed sulfur-based and
methanogenic microbes as players in the Dresser environment, the researchers
write in their report.
Other
compounds contained inside the inclusions could have served as 'building
blocks' for different carbon-based chemical reactions, in addition to chemicals
that may have acted as nutrients or substrates, processes that may have kicked
off microbial metabolism by generating energy sources, such as lipids, that
could be broken down by life forms.
In other
words, in the Dresser setting, essential ingredients of methyl triacetate, a
proposed critical agent in the emergence of life, were available, the team
explains.
The
building blocks for chemoautotrophic carbon fixation and thus anabolic carbon
absorption into biomass may have been transmitted by them.
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