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On the New Mechanism of Amino Acid Synthesis
and its Repercussion s in the Larger Field
Ziyi Yang
Amino acid s are one of the most fundamental building blocks of life. The first step
towards the formation of life is the synthesis of amino acids. To solve the puzzle of origin of
life on Earth, many scientists and researchers work on the explanation of the very first am ino
acid creation on our planet. In Zita Martins and her team ‘s study (Martins et al., 2013) , the
researchers design experiments to verify whether amino acids could be synthesized when an
impact shock is applied to a typical cometary ice mixture , a process known as shock synthes is.
They shoot ice mixtures with similar composition to a comet with a steel projectile in a light
gas gun to simulate the conditions when a rocky object clashes with icy surface , such as
comets , or when an icy object coll ides with rock surface , such as Jovian and Saturnian
satellites . The result is a detectable amount of several amino acids. This work has large
implications on the existence of life across the whole solar system. Also, this paper provides
a novel mechanism in which the first amino acids on Earth might have been synthesized as
opposed to the delivery hypothesis and Earth -pool hypothesis , which would be further
explained . Finally , t hese seemingly contradictory theories in fac t complement each other to
form a panorama of th is very inquiry of amino acid s and cooperate to answer an even larger
puzzle: when did life first emerge on Earth?
Martin ‘s study is pretty valuable in the context that many organic substances were
detected by Cassini -Huygens. Acco rding to Ostro and his group (Ostro et al., 2006), data
from radar albedos (percentage of reflection detected by radar) show contamination of
near -surface water ice in Saturnian satellites, which could be caused by compounds like

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ammonia, silicates, and metallic oxides. That is to say , the chemical condition on the surface
of these satellites could resemble that of the ice mixture in Martins’ experiments (Martins et
al., 2013) . I t is then possible that amino acids were created when rocky objects collide with
these satellites. It is well supported by astronomical observations that there are a great
amount of impacts between asteroids and meteorites with planetary or satellite surfaces every
year , and one impact in the right place at the right time would create amino acids thanks to
the mechanism of shock synthesis. Therefore, it is highly possible that apart from Earth, some
other planets or satellites in the Solar System harbor life.
The same point is alluded to i n media’s portray of this inquiry (Alan Boyle and Science
Editor, 2013) , which says that the discovery of shock synthesis increases the possibility that
life is widespread across the S olar System. With the help of the media ‘s interpretation, t he
public would gain an insight in the origin of very first building blocks of the solar system and
be more likely to support further aerospace exploration especially when huge governmental
funding is needed. They would also gain an appreciation of the diversity of our solar system
now t hat Earth might not be the only life -harboring planet.
The study of shock synthesis also offers a new mechanism through which the first amino
acids found their way to Earth. Organic compounds are common with in the parent body of
carbonaceous (containing compounds of carbon) meteorites, and these compounds could
have reacted under the high temperature and high pressure during an impact , following the
pathway provided by Martins’ shock synthesis experiments (Martins et al., 2013). There were
questions conc erning whether the amino acid products could endure such extreme physical
conditions, but it is mostly resolved by E. Pierazzo and C. F. Chyba’s study ( Pierazzo and

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Chyba, 1999) on amino acid survival in large cometary impacts. They argue that small
comets would explode in the atmosphere following Tunguska projectile so that not all
organics would be destroyed during the impacts . A lso, part of the amino acids could endure
the shock heating of large cometary impacts so if they are created by shock synthesis, some
would remain intact and make further polymerization (combin ing of amino acids to form
proteins) possible. Further, in grazing impacts where the angle of entry into atmosphere is
oblique, the peak temperature and pressure during impacts would be lower , allowing
potentially formed amino acids to survive.
Interestingly, in the larger field, there are quite different theories explaining how amino
acids came into being on Earth. In N. R. Lerner’s study (Lerner et al., 1993) , the authors
propose the Strecker synthesis as a source of amino acids in carbonaceous chondrites to
explain the ir deuterium (hydrogen -2) enrichment (also as D -enrichment, a process where the
ratio of hydrogen -2 to hydrogen -1 atoms becomes higher) . D-enrichment indicates
components from i nterstellar precursors, so meteorites and comets are probably the carriers
of these D -enriched amino acids that in turn result in the D -enrichment of chondrites .
Lerner’s experiment shows that the retention of deuterium in amino acids produced by
Strecker’ s reaction is as high as the retention rate in those chondrites ( as much as 50% ),
making itself a plausible pathway for amino acid synthesis in meteorite parent bodies. This
mechanism is different from that proposed by Martins and her team (Martins et al., 2013)
since in this case, chemical reactions happen inside the meteorites and comets , and amino
acids are carried by these astronomical objects to the Earth rather than being created from
organic precursors on the meteorites and comets duri ng the very impacts . In addition,

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unlabeled amino acids (those not deuterium -enriched) are also formed under the conditions of
Strecker reaction , indicating multiple pathways for the synthesis of amino acids in meteorites
and comets.
Furthermore, in José Aponte’s study (Aponte et al., 2017), the authors explore the
synthetic route of amino acids that leads to their occurrence in side meteorites, including both
interstellar and parent body phase. Their analysis suggests that glycine and methylamine
could hav e formed in meteoritic parent bodies , which is backed by carbon -13 (carbon atoms
with 7 neutrons) isotopic analysis . Therefore, meteorites inside which the amino acids are
already synthesized could have brought the very first glycine and methylamine to Earth , right
consistent with the delivery hypothesis that suggests meteorites are carriers of building blocks
of life.
Some studies also suggest that amino acids could be synthesized with the ingredients on
prebiotic Earth regardless of extraterrestrial i nfluences. Gheorghe Surpateanu indicates in his
study ( Surpateanu , 2018) that the first proteinogenic amino acids and their corresponding
polypeptides (short chains of amino acids linked together) could have been formed starting
with three syntones : methylene (CH 2), nitrene (NH) , and carbon monoxide (CO) . These
syntones go through a series of multi -step reactions with components from primordial
atmosphere of Earth and yield amino acids and polypeptides. The author argues that with the
presence of thes e three precursors ( CH 2, NH, and CO ) in an atmosphere with necessary
components such as water, ammonia, and hydrogen sulfide, chemical reactions naturally take
place and amino acids are yielded . Some of the intermediary products during this process
would b e analogous to the chemical composition of interstellar precursors , but are purely

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terrestrial , so the exogenous influence appears less important in the context of this paper. The
synthesis of amino acids could be spontaneous given the primordial environment on Earth.
Although many papers present diversely different theories, t he mechanism of shock
synthesis proposed by Martins and her group (Martins et al., 2013) i s also backed by other
works . In Yoshihiro Furukawa’s study (Furukawa et al., 2015), the authors indicate that
although exogenous delivery of amino acids and nucleobases is the prevailing hypothesis, the
variety and amounts of intact organics produced woul d be limited in that way. They contend
that interplanetary dust particles and crater -forming objects (evidence of shock impact
synthesis ) account for a far higher mass flux of carbon to the ancient Earth than chondrites
(evidence of delivery hypothesis ). T hus, s hock synthesis seems a more plausible hypothesis
in this case, or at least it is proposed to be the dominant source of amino acids. Also, t heir
experimental simulation results demonstrate the possibility of synthesis of amino acids and
nucleobases un der prebiotic Earth surface conditions , which agrees with Martins ‘ results
(Martins et al., 2013) . Both Furukawa’s and Martins’ simulations demonstrate that shock
impact is a possible source of amino acid synthesis, but Furukawa ‘s team goes further to
argue that this would be a more dominant mechanism than extraterrestrial delivery of
organics (Furukawa et al., 2015) .
We could see from this debat e within the field that every paper has its own focus and
point of view. It is common that their different approaches result in different conclusions
about a single question : i n this case, how amino acids first came to Earth. Some papers focus
on the formation of amino acids in meteorites and comets themselves and conclude that these
building bl ocks of life were previously well -prepared in those astronomical objects and then

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delivered to Earth. Some studies including the one by Martins et al. concern about the
creation of amino acids through the process of shock impacts, and thus conclude that sh ock
impacts of meteorites and comets on Earth surface could be the source of amino acids. Other
research discuss es independent synthetic pathways in the primordial atmosphere and
conclude s that amino acids could have formed spontaneously on Earth. Indeed, it’s hard to
say which paper is “wrong”, since every paper has its own basis and reasoning. It’s more
appropriate to think of all these ideas as complementary to each other. There could be more
than one mechanism how amino acids found their way to Earth and p erhaps all of these
hypotheses are true: some were directly delivered by meteorites and comets, some created in
the process of impacts, and others formed by terrestrial ingredients alone. These pathways are
not really exclusive to each other, but pro bably form a whole picture about the very inquiry.
Finally, these mechanisms provide insight into when life first emerged on Earth. Ben
K.D. Pearce and his team (Pearce et al., 2018) explain in their paper how the information on
early meteorite impacts is central to the inquiry of when life first appeared on Earth. The very
mechanism of amino acid synthesis and retention could potentially answer a hard question:
could life endure the Late Heavy Bombardment (LHB), a period of early Earth history where
a huge number o f asteroids collided with Earth ? If shock impacts could create amino acids,
these building blocks of life could have possibly endured harsh environment of primordial
Earth where bombardments were so common and kept evolving into the earliest life . E.
Pierazzo and C. F. Chyba ( Pierazzo and Chyba, 1999) shows that a small portion of amino
acids could survive during every impact, so probably during LHB, the earliest pre -life forms
across the globe were largely decimated, but some would always endure. Raw materials were

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constantly refurnished by comet delivery (Aponte et al., 2017) or impact synthesis (Martins et
al., 2013) so that a small group of organics could keep evolving without disturbance. And if
so, the time taken for life to form on a planet would be significantly longer compared to the
case where all previous lives were w iped out during the LHB period.
In summary, Martins and her team ‘s study suggests it is possible that organic lives are
spread across the Solar System and thus shows a future exploration is crucial. Further, the
study provides a different point of view on how early life emerged on Earth and contributes
to a larger picture. In the end, it turns out that these different theories could also work
together to resolve a deeper quest ion concerning the timescale of life evolution and have
much further repercussions.

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Reference
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