Le
- 1
The Existence of Amino Acids in Carbonaceous Chondrites
Abstract
C2 meteorites compose a high abundance of amino acids similarly found in Earth’s organic components.
Through research, some of the materials were also to be found in C2 extracts unknown in primitive meteorites.
Past research faced trivial questions that the reason for C2 meteorites to carry such abundance of life is because
of the possibility in the contamination of the Earth’s atmosphere. As these meteorites fall through the Earth’s
atmosphere under extravagant heat, the C2 components have been studied that heat does not cause corruption or
decomposition in the amino acids (1). The CM2 or Murchison meteorites have been studied because of its
diversity. It contains a possible understanding of the earliest stages of the solar system and when Earth began its
formation. Earth contained no life or organic components at its early age. The identification of the amino acids
can be found through the process of acid hydrolysis and pyrolysis (1, 6). However, under extreme heat in
similarity to the temperature of Earth’s early stage of life – no amino acids were present. Biochemical and
organic chemical concepts supply in the understanding of the complex structures within the components of the
Murchison meteorites and within other carbonaceous chondrites. This result brings an understanding of a
possibility in life existing somewhere else in space, but the struggle of understanding the complexity of the
galaxy still continues.
I. Introduction: The Analysis of Earth and Carbonaceous Chondrites
In 1969, several parts of Melbourne, Australia led to the first major discoveries of the C2 meteorites –
the Murchison meteorite. A discovery occurred after thorough gas chromatography and mass spectrometry tests
shown an existence of similar structures of their amino acids (1,3,5). This study branched off into different
types of C2 meteorites after Cronin and Pizzarello’s research. The Murchison meteorite became well-known by
its unique characteristics and composition. The meteorite composed of millions of types of organic components
by a mere 10 gram sample. The CM2 meteorite became unique and brought the birth for the study of amino
acids existing in carbonaceous chondrites. Levy, Grayson and Wolf and Lawless continued to branch this field
of study from the knowledge of Cronin and Pizzarello to conclude results with present-day high tech lab
machinery. The results of existing amino acids found in meteorites immediately assumed of possible life to be
occurring other than Earth.
The life of Carl Sagan’s, “pale blue dot,” characterizes a similar complex structure among the building
blocks of life in carbonaceous chondrites. This study may conclude to a coexistence of life elsewhere in the
universe other than Earth’s boundaries. These meteorites carry an abundance of organic components. However,
the meteorites that have been collected are being questioned for the cause of chemical evolution or for carrying
extraterrestrial components or to be caused by the contamination of Earth. CM2 meteorites such as the
Murchison meteorite carry the history of the early stages of the solar system. Earth in the early stages of
formation and creation as a planet did not prevail the existence of life nor components of organic molecules
living on Earth during the Hadean time (6). Therefore, Glavin, Matrajt and Bada stated that these meteorites
could not be possible Earth originated substances from the past. The CM2 meteorites originated from
extraterrestrial environment was the only assumption that can be concluded in this field of study.
In 1989, Cronin and Pizzarello proved that there were small excess of life found in the amino acids of
the carbonaceous chondrites: Murray and Murchison (1). Polarimetry techniques were used to measure the
Le
- 2
optical rotations of the amino acid components. Cronin and Pizzarello have determined small excess of Lenantiomers in some of the amino acids (3, 5). The amino acids were discovered to be optically active and
contained to possess a chiral characterization of containing two enantiomers L or D. L-enantiomers of the
amino acids are studied to be the initiation source of life because of its specific structural formula (1,5). In
further study of this research, Murchison meteorites established that amino acids were indigenous to the
meteorite and were products of an abiotic chemical process (5). The Murchison meteorite confirmed to contain
an identification of approximately 52 amino acids and only 18 amino acids to be found existing on Earth. The
remaining amino acids are unfamiliar to the proteins found in biological organisms and some discovered to be
too complex for our understanding. Their discovery leads to a further investigation of the carbonaceous
chondrites. However, there is still more complexity in proving that these components perform in an abiotic
chemical process. Cronin and Pizzarello first approach their study by countering possible arguments, such as
chemical evolution. Chemical evolution requires an understanding of the conditions and facts of the atmosphere
and its space bodies and the detail of chemical synthesis. The universe is structured of different chemical
components. Glavin, Matrajt and Bada introduced their knowledge of cosmology and biochemistry that in
certain areas of the universe compose of various chemical compounds that could have exposed the amino acids
in these meteorites (6). Lawless has discovered that under higher temperatures and pressure, the concentrations
of the Murchison extract decrease in percentage of amino acids present (2). Throughout other studies in the
similar field, similar amino acids were discovered and the classifications of the structures in the complex amino
acids became easier to understand in comparison of the past and present. Cronin, Pizzarello and et. al ,
presented biochemistry components of the amino acids that compose of complex proteins in the separation of
two groups: acyclic and cyclic components (5). Acyclic and cyclic amino acids derive by obtaining different
number of carbon bonds. Originally in amino acids presented in Earth contain 2 carbon bonds and 3 different
types of groups: carboxyl group, hydrogen bond and an amino group. However, in the amino acids of the
Murchison extract can vary to 4, 5, 6 or 7 carbon bonds. Pizzarello and Cronin have also qualified that the
atmosphere’s heat does not combust the meteorites as they fall into the Earth’s atmosphere (1, 3). The amino
acids in the meteorites are not combustible under those temperatures. The thermal decomposition of the earth’s
ozone will not greatly affect the amino acid in the Murchison meteorite or in general carbonaceous chondrites
(3).
II. Different types of C2 Meteorites
Through further investigation of the amino acids presented in the Murchison meteorites, researches such
as Cronin and Pizzarello have introduced that other carbonaceous chondrites have similar properties as the
Murchison CM2 (1, 3). There are several types of carbonaceous chondrites that have been identified and
analyzed to be composed of certain biological amino acids (Fig. 1). The table displays the groups of analyzed
carbonaceous chondrites and separated by specific dates. CM2 meteorites such as Murray, Murchison and
Mighei are studied continuously because of their differences in dates. However, the Mokoia CV2, Allende CV3
and Orgueil CI1 are also studied in comparison and contrast among the other carbonaceous chondrites (1, 2, 3,
4, 5, 6). However, Glavin, Matrajt and Bada introduce the study of Antarctic micrometeorites.
Le
- 3
Figure 1. Table of analyzed amino acids in carbonaceous chondrites and separated by specific groups of their
landing dates (1).
III. Arguments in this Field of Study
Arguments involved in this field of study created a fluctuation in understanding the characteristics of the
Murchison meteorite. C2 meteorite’s unique composition became unclear to scientists due to little evidence that
Cronin and Pizzarello have obtained. Lawless, Levy, Grayson and Wolf, Glavin, Matrajt and Bada continuously
reexamined past studies of Cronin and Pizzarello to achieve new results (2, 4, 6). Arguments led to the
assumption that the development of the C2 meteorites were caused by terrestrial contamination, a chemical
evolution or a possibly extraterrestrial material. Pizzarello and Cronin stated that the C2 carbonaceous
chondrites were not Earth originated components (1, 2, 3, 5). However, Levy, Grayson and Wolf theorized that
these unique meteorites composed of a certain chemical evolution (4). Lawless counters the argument and
supports his position that C2 meteorites could not have been contaminated by Earth’s exposure (2). Glavin,
Matrajt, and Bada re-examined Cronin and Pizzarello’s research with present day machinery and possible
discovery in Antarctic micrometeorites (6). Researchers in this field of study wanted to achieve in displaying
the evidence that Cronin and Pizzarello produced believable results.
IV. Methods: Acid-Heat Hydrolysis, Ion Exchange Column & Gas Chromatography
Cronin and Pizzarello utilized methods of Gas chromatography and Ion exchange column for the
separation and identification of organic components throughout chemistry based experiments (1, 3, 5). Glavin,
Matrajt and Bada obtained their results with the usage of similar methods of Cronin and Pizzarello (6). However
Lawless and Levy, Grayson and Wolf (2, 4) have included acid hydrolysis and pyrolysis before placing the
meteorite concentration into ion exchange column. In comparison to Cronin and Pizzarello’s methods, Lawless
and Levy, Grayson and Wolf began by crushing the sample into powder. Then added water into the substance
for 20 hours, and evaporated to dryness. They repeated this step with 6 N of Hydrochloric acid for 20 hours,
diluted with water and evaporated to dryness again. This is a type of purification technique. The samples were
drained across the ion exchange column in a mixture of 2 N ammonium hydroxide and water. The distillate is
again evaporated to dryness for preparation of gas chromatography. Perkin Elmer 900 machinery was used in
Le
- 4
GC analysis. The machinery is equipped with a flame ionization detector. Lawless programmed the GC to go
under 100 to 150 degrees Celsius.
Levy, Grayson and Wolf has performed extreme conditions of pyrolysis, which makes the results more
accurate. Levy, Grayson and Wolf has performed similar procedures, but allowed the sample to be mixed with
benzene-methanol and then evaporated before GC analysis. The machinery used specializes with vaporizationpyrolysis gas chromatography. The experiment involved with two carbonaceous chondrites types: Allende –
CV3 and Murchison - CM2. The experiment was processed through a Beckman GC-4 gas chromatography with
a ceramic flame ionization detector. The particles of the sample were wrapped in foil and inserted in a test tube
and placed under 1000 degrees Celsius with Oxygen flowing through it. The gas chromatography increased in
temperature from 150 degrees Celsius, 300 degrees Celsius and 430 degrees Celsius. The Gas chromatography
is turned off and cooled to 120 degrees Celsius – recording 5 degrees Celsius per minute. Most of the
components of amino acids present were recorded to be at 150 degrees Celsius, 300 degrees Celsius and 430
degrees Celsius, anything beyond that temperature did not contain any amino acid concentration present.
Cronin and Pizzarello used techniques such as polarimetry where they discovered that the enantiomer
excesses contain L-enantiomers. Polarimetry measures the activity in optical relationships of the enantiomers
within the amino acids. Amino acids were determined to be chiral molecules that derive from two images like
components – enantiomers. In their analytical procedures, Cronin and Pizzarello obtained two pieces of Murray
meteorites. The samples were crushed and distilled with water for 24 hours at 110 degrees Celsius through a
vacuum filtration. The extracts of the Murray sample were concentrated through rotary evaporation at 100
degrees Celsius for an hour and then acidified at pH 2 with 1 N of sulfuric acid. The extracts were distilled and
evaporated to dryness and travelled through an ion exchange column with a citrate buffer. The amino acids
formed were eluted with ammonium hydroxide.
Le
- 5
V. Amino Acid Analysis
Figure 2 displays a table of the results in abundance of amino acids present in the Murchison meteorite from
Cronin and Pizzarello’s study (1, 3, 5).
Cronin and Pizzarello’s data carried similarities in other research that an approximate count of 17 to 19
possible amino acids in the meteorite extracts exist with similar structures of the amino acids found on Earth.
There is an abundance of known proteins such as Glycine found in the Murchison meteorite and an abundance
of an unknown protein, alpha-aminobutyric acid (Figure 2). Biological occurrence (B) are non-protein
biological amino acids that do not exist or not known yet in biochemistry. This leaves room for more
investigation in understanding these types of non-protein amino acids. These non-protein type amino acids have
been acknowledged to be extraterrestrial (2, 4).
Lawless and Levy, Grayson and Wolf experimented based on pyrolysis to understand the behavior of the
amino acids in the Murchison meteorite. Lawless labeled components by number on gas chromatography and
mass spectrometry graphs (figure 3, figure 4). Lawless displayed that Glycine and Isovaline obtained an
abundance of amino acids in the Murchison meteorite (figure 4). Lawless’s results obtain similar outcomes as
Le
- 6
Cronin and Pizzarello where Glycine is the most favorable amino acid found in the Murchison meteorite under
different heat standards.
Figure 3, displays the table of amino acids found in the Murchison meteorite sample that Lawless obtained.
Certain identifications were unknown and required to be speculated under high resolution under mass
spectrometry and gas spectrometry (2, 4).
Figure 4, displays the components labeled in numbers by figure 3 of the amino acids found in the Murchison
meteorite from the response of different temperatures. As the time increased with temperature being constant,
amino acids began to decline. However, Isovaline and Glycine proteins produced significant outcomes that
differ from the other amino acids (2, 4).
In Levy, Grayson and Wolf’s experiment contributed their research with the Murchison and Allende
meteorites and terrestrial rocks: Pumice and Basalt. The terrestrial rocks contained similar components of
Le
- 7
protein based amino acids found on Earth. Basalt and Pumice are treated as experimental controls for
comparing and contrasting during results. Levy, Grayson and Wolf analyzed the meteorites and terrestrial rocks
through the process of vaporization and pyrolysis. The temperature controls measured approximated from 150
degrees Celsius, 300 degrees Celsius and 430 degrees Celsius. Results concluded numerous of components
displayed fewer than 430 degree environments. Figure 5 displays the key of certain peaks of the graphs for
specific temperatures on figure 6 (figure 5, figure 6). Levy, Grayson and Wolf concludes that the meteorites
composed of non-protein biological characteristics are from outer space. The carbonaceous chondrites display a
certain abundance of unknown components found in the terrestrial rocks (4). The result can be compared with
Cronin and Pizzarello’s past studies of the certain arguments that Cronin and Pizzarello had faced (1, 3, 4).
Figure 5 displays a table of the identified products of the Murchison meteorite through pyrolysis in 430 degree
Celsius environment. The peak numbers correspond to figure 6 of the compounds present at specific
temperatures (4).
Le
- 8
Figure 6 are multiple graphs representing the presence of amino acids in the Murchison meteorite under
different temperature controls. When time increases, the concentration of the amino acids decreases. The
sample at 150 degrees Celsius displays no presence of amino acids. However, at higher temperatures, amino
acids became existent due to excitation of the protons at high temperature (1, 3, 4, 5).
Glavin, Matrajt and Bada have contributed support and evidence of the L-enantiomers of amino acids
that have been previously studied by Cronin and Pizzarello. After the sample was completely processed in
hydrolysis, pyrolysis, gas chromatography and mass spectrometry, they have diagnosed the left side amino
acids found in Antarctic micrometeorites (6). However, the Antarctic micrometeorites were not appropriate for
the research because the samples are completely Earth originated components. Glavin, Matrajt and Bada
achieved in displaying the behavior of the reason why left handed amino acids only involved and existed in the
creation of life on Earth (1, 3, 5, 6). The micrometeorites analyzed to produce similar properties as the
Murchison meteorite by their specific protein amino acids and non protein amino acids (6). On figure 7 displays
a table of the amino acids found in the Antarctic micrometeorites (figure 7). Glavin, Matrajt and Bada supports
great contribution of the theory why only L-amino acids are found to produce reproduction and creation
functions in living organisms on Earth.
Le
- 9
Figure 7 displays a table of the summary with amino acids present in Antarctic micrometeorites. Glavin, Matrajt
and Bada displays a specific analysis of the left and right handed amino acids found in the rocks measuring by
its mass through mass spectrometry (6).
VI. Conclusion: What has been discovered? What needs to be discovered? (Possible errors)
The C2 meteorites were analyzed that there was impossible interference of exposure to cause amino acid
deterioration. The meteorites have not been contaminated as they fall through Earth’s biosphere. Cronin and
Pizzarello determined arguments by studying the polarimetry of the amino acids. The carbonaceous chondrites
resulted to be optically active molecules because of its chiral characteristics. To be a chiral molecule means to
have left and right components (L-enantiomer or D-enantiomer). According to Cronin and Pizzarello, the Lenantiomer has been processed under amino acid analysis to have some or little L-enantiomer excess (1, 2, 3).
L-enantiomer excess contains the abundance of organic components and 2 carbon bonds in the amino acids.
Glavin, Matrajt and Bada have supported Cronin and Pizzarello’s data by contributing their research with
present day advanced technology (6). This concludes that the carbonaceous chondrites are not Earth originated.
Levy, Grayson and Wolf’s experiment assured that the study of the comparison between terrestrial
rocks and carbonaceous chondrites show a relationship of the other. The terrestrial rocks: Pumice and Basalt
composed of certain organic components; they somehow contain non-protein based amino acids similarly found
in some of the carbonaceous chondrites. Their result displays that carbonaceous chondrites are originated from a
foreign place – not a returning rock from Earth (4). Levy, Grayson and Wolf, Grayson and Wolf have also
showed the correlation that certain heat levels do not corrupt the structure of the amino acids. Levy, Grayson
and Wolf suggested a continuation of the experiment because of possible errors that Cronin and Pizzarello have
introduced (1, 3, 4, 5). A possible error that can occur through an experiment is the co-elution of the meteorites,
when two substances mixed together cannot be mixed – not miscible (1, 3). Hopefully someday humanity can
safely assume that there is a possible life elsewhere than our “pale blue dot.” The founding fathers of biological
Le
- 10
sciences, Charles Darwin recognize how each microorganism is treated as a minuscule universe itself. The
tiniest organisms reproduce numerously as the stars of our universe.
VII. References
[1] Cronin, J.R.; Pizzarello, S. Amino acids in Meteorites. Advances in Space Research. 1983. 3:5-18.
[2] Lawless, J.G., Amino Acids in the Murchison Meteorite. Geochimica et Cosmochimica Acta. 1973. 37:
2207-2212.
[3] Cronin, J.R., Pizzarello, S, et. al. Amino Acids of the Murchison Meteorite: II. Five Acyclic Primary β-,
ϒ- and σ-Amino Alkanoic Acids. Geochimica et Cosmochimica Acta. 1985. 49: 2259-2265.
[4] Levy, R.L., Grayson, M.A., et. Al. The Organic Analysis of the Murchison Meteorite. Geochimica et
Cosmochimica Acta. 1973. 37:467-483.
[5] Pizzarello, S., Cronin, J.R. Non-racemic Amino Acids in the Murray and Murchison Meteorites.
Geochimica et Cosmochimica Acta. 2000. 64: 329-338.
[6] Glavin, D.P., Matrajt, G., Bada, J.L. Re-examination of amino acids in Antarctic micrometeorites. Advances
in Space Research. 2004. 33: 106-113.