Murchison meteorite

The Murchison meteorite is a meteorite that fell in Australia in 1969 near Murchison, Victoria. It belongs to a group of meteorites rich in organic compounds. Due to its mass (over 100 kg or 220 lb) and the fact that it was an observed fall, the Murchison meteorite is one of the most studied of all meteorites.

Murchison meteorite
A Murchison meteorite specimen at the National Museum of Natural History, Washington, D.C.
Type	Chondrite
Class	Carbonaceous chondrite
Group	CM2
Composition	22.13% total iron, 12% water
Shock stage	S1–2
Country	Australia
Region	Victoria
Coordinates	36°37′S 145°12′E[1]
Observed fall	Yes
Fall date	28 September 1969
TKW	100 kg (220 lb)
Pair of grains from the Murchison meteorite
Related media on Wikimedia Commons

In January 2020, cosmochemists reported that the oldest material found on Earth to date is the silicon carbide particles from the Murchison meteorite, which have been determined to be 7 billion years old, about 2.5 billion years older than the 4.54-billion-year age of the Earth and the Solar System.[lower-alpha 1] The published study noted that "dust lifetime estimates mainly rely on sophisticated theoretical models. These models, however, focus on the more common small dust grains and are based on assumptions with large uncertainties."[2]

History

On 28 September 1969 at approximately 10:58 a.m. local time, near Murchison, Victoria, in Australia, a bright fireball was observed to separate into three fragments before disappearing,[1] leaving a cloud of smoke. About 30 seconds later, a tremor was heard. Many fragments were found scattered over an area larger than 13 square kilometres (5.0 sq mi), with individual mass up to 7 kilograms (15 lb); one, weighing 680 grams (1.5 lb), broke through a roof and fell in hay.[1] The total collected mass of the meteorite exceeds 100 kilograms (220 lb).[3]

Classification and composition

The meteorite belongs to the CM group of carbonaceous chondrites. Like most CM chondrites, Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body[4] before falling to Earth. CM chondrites, together with the CI group, are rich in carbon and are among the most chemically primitive meteorites.[5] Like other CM chondrites, Murchison contains abundant calcium-aluminium-rich inclusions. More than 15 amino acids, some of the basic components of life, have been identified during multiple studies of this meteorite.[6]

In January 2020, astronomers reported that Murchison meteorite silicon carbide particles had been determined to be 7 billion years old, 2.5 billion years older than the 4.54 billion years age of the Earth and the solar system, and the oldest material found on Earth to date.[7][2]

Organic compounds

Fragment of the Murchison meteorite (at right) and isolated individual particles (shown in the test tube)

Murchison contains common amino acids such as glycine, alanine, and glutamic acid as well as unusual ones such as isovaline and pseudoleucine.[8] A complex mixture of alkanes 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 acids was identified in the Murchison meteorite as well.[9]

The initial report stated that the amino acids were racemic and therefore formed in an abiotic manner, because amino acids of terrestrial proteins are all of the L-configuration. Later the amino acid alanine, which is also a protein amino acid, was found to have an excess of the L-configuration,[10] which led several scientists to suspect terrestrial contamination according to the argument that 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".[11] In 1997, L-excesses also were found in a non-protein amino acid, isovaline,[12] suggesting an extraterrestrial source for molecular asymmetry in the solar system. At the same time, L-excesses of alanine were found in Murchison, but with enrichment in the isotope ¹⁵N,[13] however, the isotopic pairing was contested later, on analytical grounds.[14] By 2001, the list of organic materials identified in the meteorite was extended to polyols.[15]

Compound class[16]	Concentration (ppm)
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
Sulfonic acids	68
Phosphonic acids	2
Total	>3911.3

The meteorite contained a mixture of left-handed and right-handed amino acids; most amino acids used by living organisms are left-handed in chirality, and most sugars used are right-handed. A team of chemists in Sweden demonstrated in 2005 that this homochirality could have been triggered or catalyzed, by the action of a left-handed amino acid such as proline.[17]

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.[18][19] 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.[20]

Nucleobases

Further information: Nucleobase

Measured purine and pyrimidine compounds were found in the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of δ¹³C = +44.5‰ and +37.7‰, respectively, indicate a non-terrestrial origin for these compounds. This specimen demonstrates that many organic compounds could have been delivered by early solar system bodies and may have played a key role in life's origin.[21]

See also

• Cosmochemistry
• Glossary of meteoritics

Notes

1. That makes the stardust grains in the Murchison meteorite presolar grains, since they originated at a time before the Sun was formed.

References

1. Meteoritical Bulletin Database: Murchison
2. Heck, Philipp R.; Greer, Jennika; Kööp, Levke; Trappitsch, Reto; Gyngard, Frank; Busemann, Henner; Maden, Colin; Ávila, Janaína N.; Davis, Andrew M.; Wieler, Rainer (13 January 2020). "Lifetimes of interstellar dust from cosmic ray exposure ages of presolar silicon carbide". Proceedings of the National Academy of Sciences. 117 (4): 1884–1889. Bibcode:2020PNAS..117.1884H. doi:10.1073/pnas.1904573117. PMC 6995017. PMID 31932423.
3. Pepper, F. When a space visitor came to country Victoria Archived 1 October 2019 at the Wayback Machine ABC News, 2 October 2019. Retrieved 2 October 2019.
4. Airieau, S. A.; Farquhar, J.; Thiemens, M. H.; Leshin, L. A.; Bao, H.; Young, E. (2005). "Planetesimal sulfate and aqueous alteration in CM and CI carbonaceous chondrites". Geochimica et Cosmochimica Acta. 69 (16): 4167–4172. Bibcode:2005GeCoA..69.4167A. CiteSeerX 10.1.1.424.6561. doi:10.1016/j.gca.2005.01.029.
5. "Planetary Science Research Discoveries: Glossary". Archived from the original on 24 January 2012. Retrieved 24 January 2012.
6. Wolman, Yecheskel; Haverland, William J.; Miller, Stanley L. (April 1972). "Nonprotein Amino Acids from Spark Discharges and Their Comparison with the Murchison Meteorite Amino Acids". Proceedings of the National Academy of Sciences. 69 (4): 809–811. Bibcode:1972PNAS...69..809W. doi:10.1073/pnas.69.4.809. PMC 426569. PMID 16591973.
7. Weisberger, Mindy (13 January 2020). "7 Billion-Year-Old Stardust Is Oldest Material Found on Earth - Some of these ancient grains are billions of years older than our sun". Live Science. Archived from the original on 14 January 2020. Retrieved 13 January 2020.
8. Kvenvolden, Keith A.; Lawless, James; Pering, Katherine; Peterson, Etta; Flores, Jose; Ponnamperuma, Cyril; Kaplan, Isaac R.; Moore, Carleton (1970). "Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite". Nature. 228 (5275): 923–926. Bibcode:1970Natur.228..923K. doi:10.1038/228923a0. PMID 5482102.
9. Meierhenrich, Uwe J.; Bredehöft, Jan Hendrik; Jessberger, Elmar K.; Thiemann, Wolfram H.-P. (2004). "Identification of diamino acids in the Murchison meteorite". PNAS. 101 (25): 9182–9186. Bibcode:2004PNAS..101.9182M. doi:10.1073/pnas.0403043101. PMC 438950. PMID 15194825.
10. Engel, Michael H.; Nagy, Bartholomew (29 April 1982). "Distribution and enantiomeric composition of amino acids in the Murchison meteorite". Nature. 296 (5860): 837–840. Bibcode:1982Natur.296..837E. doi:10.1038/296837a0.
11. Bada, Jeffrey L.; Cronin, John R.; Ho, Ming-Shan; Kvenvolden, Keith A.; Lawless, James G.; Miller, Stanley L.; Oro, J.; Steinberg, Spencer (10 February 1983). "On the reported optical activity of amino acids in the Murchison meteorite". Nature. 301 (5900): 494–496. Bibcode:1983Natur.301..494B. doi:10.1038/301494a0.
12. Cronin, John R.; Pizzarello, S. (1997). "Enantiomeric excesses in meteoritic amino acids". Science. 275 (5302): 951–955. Bibcode:1997Sci...275..951C. doi:10.1126/science.275.5302.951. PMID 9020072.
13. Engel, Michael H.; Macko, S. A. (1 September 1997). "Isotopic evidence for extraterrestrial non-racemic amino acids in the Murchison meteorite". Nature. 389 (6648): 265–268. Bibcode:1997Natur.389..265E. doi:10.1038/38460. PMID 9305838.
14. Pizzarello, Sandra; Cronin, JR (1998). "Alanine enantiomers in the Murchison meteorite". Nature. 394 (6690): 236. Bibcode:1998Natur.394..236P. doi:10.1038/28306. PMID 9685155.
15. Cooper, George; Kimmich, Novelle; Belisle, Warren; Sarinana, Josh; Brabham, Katrina; Garrel, Laurence (20 December 2001). "Carbonaceous meteorites as a source of sugar-related organic compounds for the early Earth". Nature. 414 (6866): 879–883. Bibcode:2001Natur.414..879C. doi:10.1038/414879a. PMID 11780054. Archived from the original on 16 January 2020. Retrieved 2 July 2019.
16. Machalek, Pavel (17 February 2007). "Organic Molecules in Comets and Meteorites and Life on Earth" (PDF). Department of Physics and Astronomy. Johns Hopkins University. Archived from the original (PDF) on 17 December 2008. Retrieved 7 October 2008.
17. Córdova, Armando; Engqvist, Magnus; Ibrahem, Ismail; Casas, Jesús; Sundén, Henrik (2005). "Plausible origins of homochirality in the amino acid catalyzed neogenesis of carbohydrates". Chem. Commun. (15): 2047–2049. doi:10.1039/b500589b. PMID 15834501.
18. Walton, Doreen (15 February 2010). "Space rock contains organic molecular feast". BBC News. Archived from the original on 16 February 2010. Retrieved 15 February 2010.
19. Schmitt-Kopplin, Philippe; Gabelica, Zelimir; Gougeon, Régis D.; Fekete, Agnes; Kanawati, Basem; Harir, Mourad; Gebefuegi, Istvan; Eckel, Gerhard; Hertkorn, Norbert (16 February 2010). "High molecular diversity of extraterrestrial organic matter in Murchison meteorite revealed 40 years after its fall" (PDF). PNAS. 107 (7): 2763–2768. Bibcode:2010PNAS..107.2763S. doi:10.1073/pnas.0912157107. PMC 2840304. PMID 20160129. Archived from the original on 2 December 2012. Retrieved 16 February 2010.
20. Matson, John (15 February 2010). "Meteorite That Fell in 1969 Still Revealing Secrets of the Early Solar System". Scientific American. Archived from the original on 19 March 2011. Retrieved 15 February 2010.
21. Martins, Zita; Botta, Oliver; Fogel, Marilyn L.; Sephton, Mark A.; Glavin, Daniel P.; Watson, Jonathan S.; Dworkin, Jason P.; Schwartz, Alan W.; Ehrenfreund, Pascale (20 March 2008). "Extraterrestrial nucleobases in the Murchison meteorite" (PDF). Earth and Planetary Science Letters. 270 (1–2): 130–136. arXiv:0806.2286. Bibcode:2008E&PSL.270..130M. doi:10.1016/j.epsl.2008.03.026. Archived from the original (PDF) on 10 August 2011. Retrieved 7 October 2008.

External links

• Rosenthal, Anne M. (12 February 2003). "Murchison's Amino Acids: Tainted Evidence?". Astrobiology Magazine.
• Matson, John (15 February 2010). "Meteorite That Fell in 1969 Still Revealing Secrets of the Early Solar System". Scientific American.

 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.