Murchison meteorite
Encyclopedia
The Murchison meteorite is named after Murchison, Victoria
, in Australia
. It is one of the most studied meteorite
s due to its large mass (>100 kg), the fact that it was an observed fall, and it belongs to a group of meteorites rich in organic compound
s.
in Australia
, a bright fireball was observed to separate into three fragments before disappearing, leaving a cloud of smoke. About 30 seconds later, a tremor was heard. Many specimens were found over an area larger than 13 km², with individual masses up to 7 kg; one, weighing 680 g, broke through a roof and fell in hay. The total collected mass exceeds 100 kg.
s (see meteorite classification). Like most CM chondrites, Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body before falling to Earth. CM chondrites, together with the CI group, are rich in carbon and are among the most chemically primitive meteorites in our collections. Like other CM chondrites, Murchison contains abundant CAIs. Over 100 amino acid
s (some of the basic components of life) have been identified in the meteorite.
s such as glycine
, alanine
and glutamic acid
as well as unusual ones like isovaline
and pseudoleucine. The initial report stated that the amino acids were racemic
(that is, the chirality
of their enantiomer
s are equally left- and right-handed), indicating that they are not present due to terrestrial contamination. A complex mixture of alkane
s was isolated as well, similar to that found in the Miller-Urey experiment
. Serine
and threonine
, usually considered to be earthly contaminants, were conspicuously absent in the samples. A specific family of amino acids called diamino acid
s was identified in the Murchison meteorite as well.
More research found that some amino acids were present in enantiomeric excess
, leading some to suspect terrestrial contamination, since it would be "unusual for an abiotic stereoselective decomposition or synthesis of amino acids to occur with protein amino acids but not with non-protein amino acids." In 1997 research showed that individual amino-acid enantiomers from Murchison were enriched in the nitrogen isotope
15N relative to their terrestrial counterparts, which confirmed an extraterrestrial source for an L-enantiomer excess in the Solar System. The list of organic materials identified in the meteorite was extended to polyol
s by 2001.
Building on the idea that homochirality
(existence of only left-handed amino acids and right-handed sugars) is triggered by deposition of chiral molecules on meteorites, research in 2005 demonstrated that an amino acid like L-proline
is capable of catalyzing the formation of chiral sugars. The catalysis
is non-linear, that is proline with an enantiomeric excess
of 20% yields an allose
with enantiomeric excess of 55% starting from a benzyloxyacetaldehyde in a sequential aldol
type reaction in an organic solvent like DMF
. In other words a small enantiomeric excess of left-handed amino acids may explain terrestrial life's preference for right-handed sugars.
Several lines of evidence indicate that the interior portions of well-preserved fragments from Murchison are pristine. A 2010 study using high resolution analytical tools including spectroscopy
, identified 14,000 molecular compounds including 70 amino acids in a sample of the meteorite. The limited scope of the analysis by mass spectrometry provides for a potential 50,000 or more unique molecular compositions, with the team estimating the possibility of millions of distinct organic compounds in the meteorite.
and pyrimidine
compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil
and xanthine
of 44.5‰ and +37.7‰, respectively, indicate a non-terrestrial origin for these compounds. These results demonstrate that many organic compounds which are components of life on Earth, were already present in the early solar system and may have played a key role in life's origin.
Murchison, Victoria
Murchison is a small rural village located on the Goulburn River in Victoria, Australia. Murchison is located 167 kilometres from Melbourne and is just to the west of the Goulburn Valley Highway between Shepparton and Nagambie. The surrounding countryside contains orchards, vineyards and dairy...
, in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. It is one of the most studied meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s due to its large mass (>100 kg), the fact that it was an observed fall, and it belongs to a group of meteorites rich in organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
s.
History
On 28 September 1969 at about 10:58 AM, near the town of Murchison, VictoriaMurchison, Victoria
Murchison is a small rural village located on the Goulburn River in Victoria, Australia. Murchison is located 167 kilometres from Melbourne and is just to the west of the Goulburn Valley Highway between Shepparton and Nagambie. The surrounding countryside contains orchards, vineyards and dairy...
in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, a bright fireball was observed to separate into three fragments before disappearing, leaving a cloud of smoke. About 30 seconds later, a tremor was heard. Many specimens were found over an area larger than 13 km², with individual masses up to 7 kg; one, weighing 680 g, broke through a roof and fell in hay. The total collected mass exceeds 100 kg.
Classification and composition
The meteorite belongs to the CM group of carbonaceous chondriteCarbonaceous chondrite
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites...
s (see meteorite classification). Like most CM chondrites, Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body before falling to Earth. CM chondrites, together with the CI group, are rich in carbon and are among the most chemically primitive meteorites in our collections. Like other CM chondrites, Murchison contains abundant CAIs. Over 100 amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s (some of the basic components of life) have been identified in the meteorite.
Organic matter
Murchison contains common amino acidAmino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s such as glycine
Glycine
Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...
, alanine
Alanine
Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 amino acids encoded by the genetic code. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...
and glutamic acid
Glutamic acid
Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salts of glutamic acid are known as glutamates...
as well as unusual ones like isovaline
Isovaline
Isovaline is a rare amino acid that was found in the Murchison meteorite. It is an isomer of the biologically important amino acid valine. It may have analgesic properties....
and pseudoleucine. The initial report stated that the amino acids were racemic
Racemic
In chemistry, a racemic mixture, or racemate , is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. The first known racemic mixture was "racemic acid", which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid.- Nomenclature :A...
(that is, the chirality
Chirality (chemistry)
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....
of their enantiomer
Enantiomer
In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...
s are equally left- and right-handed), indicating that they are not present due to terrestrial contamination. A complex mixture of alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...
s was isolated as well, similar to that found in the Miller-Urey experiment
Miller-Urey experiment
The Miller and Urey experiment was an experiment that simulated hypothetical conditions thought at the time to be present on the early Earth, and tested for the occurrence of chemical origins of life. Specifically, the experiment tested Alexander Oparin's and J. B. S...
. Serine
Serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
and threonine
Threonine
Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...
, usually considered to be earthly contaminants, were conspicuously absent in the samples. A specific family of amino acids called diamino acid
Diamino acid
In chemistry, a diamino acid, also called a diamino carboxylic acid, is a molecule containing at least one carboxyl and two amine functional groups. Diamino acids belong to the class of amino acids.- Biochemical function :...
s was identified in the Murchison meteorite as well.
More research found that some amino acids were present in enantiomeric excess
Enantiomeric excess
The enantiomeric excess of a substance is a measure of how pure it is. In this case, the impurity is the undesired enantiomer .-Definition:...
, leading some to suspect terrestrial contamination, since it would be "unusual for an abiotic stereoselective decomposition or synthesis of amino acids to occur with protein amino acids but not with non-protein amino acids." In 1997 research showed that individual amino-acid enantiomers from Murchison were enriched in the nitrogen isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
15N relative to their terrestrial counterparts, which confirmed an extraterrestrial source for an L-enantiomer excess in the Solar System. The list of organic materials identified in the meteorite was extended to polyol
Polyol
A polyol is an alcohol containing multiple hydroxyl groups. In two technological disciplines the term "polyol" has a special meaning: food science and polymer chemistry.- Polyols in food science :...
s by 2001.
| Compound class | Concentration (ppm PPM - Culture :*Peter, Paul and Mary, a 1960s folk music trio*Picture Postcard Monthly, a magazine for collectors of postcards*Please Please Me, the first album by The Beatles- Health :*Permanent pacemaker or artificial pacemaker... ) |
|---|---|
| Amino acids | 17-60 |
| Aliphatic hydrocarbons | >35 |
| Aromatic hydrocarbons | 3319 |
| Fullerenes | >100 |
| Carboxylic acids | >300 |
| Hydrocarboxylic acids | 15 |
| Purines and Pyrimidines | 1.3 |
| Alcohols | 11 |
| Sulphonic acids | 68 |
| Phosphonic acids | 2 |
Building on the idea that homochirality
Homochirality
Homochirality is a term used to refer to a group of molecules that possess the same sense of chirality. Molecules involved are not necessarily the same compound, but similar groups are arranged in the same way around a central atom. In biology homochirality is found in the chemical building blocks...
(existence of only left-handed amino acids and right-handed sugars) is triggered by deposition of chiral molecules on meteorites, research in 2005 demonstrated that an amino acid like L-proline
Proline
Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the α-amino group is secondary...
is capable of catalyzing the formation of chiral sugars. The catalysis
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
is non-linear, that is proline with an enantiomeric excess
Enantiomeric excess
The enantiomeric excess of a substance is a measure of how pure it is. In this case, the impurity is the undesired enantiomer .-Definition:...
of 20% yields an allose
Allose
Allose is an aldohexose sugar. It is a rare monosaccharide that has been isolated from the leaves of the African shrub Protea rubropilosa. It is soluble in water and practically insoluble in methanol.Allose is a C-3 epimer of glucose....
with enantiomeric excess of 55% starting from a benzyloxyacetaldehyde in a sequential aldol
Aldol reaction
The aldol reaction is a powerful means of forming carbon–carbon bonds in organic chemistry.Discovered independently by Charles-Adolphe Wurtz and Alexander Porfyrevich Borodin in 1872, the reaction combines two carbonyl compounds to form a new β-hydroxy carbonyl compound...
type reaction in an organic solvent like DMF
Dimethylformamide
Dimethylformamide is an organic compound with the formula 2NCH. Commonly abbreviated as DMF , this colourless liquid is miscible with water and the majority of organic liquids. DMF is a common solvent for chemical reactions...
. In other words a small enantiomeric excess of left-handed amino acids may explain terrestrial life's preference for right-handed sugars.
Several lines of evidence indicate that the interior portions of well-preserved fragments from Murchison are pristine. A 2010 study using high resolution analytical tools including spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
, identified 14,000 molecular compounds including 70 amino acids in a sample of the meteorite. The limited scope of the analysis by mass spectrometry provides for a potential 50,000 or more unique molecular compositions, with the team estimating the possibility of millions of distinct organic compounds in the meteorite.
Nucleobases
Measured purinePurine
A purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
and pyrimidine
Pyrimidine
Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring...
compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil
Uracil
Uracil is one of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U. The others are adenine, cytosine, and guanine. In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine.Uracil is a common and...
and xanthine
Xanthine
Xanthine , is a purine base found in most human body tissues and fluids and in other organisms. A number of stimulants are derived from xanthine, including caffeine and theobromine....
of 44.5‰ and +37.7‰, respectively, indicate a non-terrestrial origin for these compounds. These results demonstrate that many organic compounds which are components of life on Earth, were already present in the early solar system and may have played a key role in life's origin.