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Home , Cosmochemistry, Molecule, Sandra Pizzarello

Mètode Studies Journal ISSN: 2174-3487 [email protected] Universitat de València España

Pizzarellllo, Sandra LOOKING FOR THE ORIGIN OF IN ASTEROIDS AND THEIR -RICH Mètode Science Studies Journal, núm. 6, 2016, pp. 161-165 Universitat de València Valencia, España

Available in: http://www.redalyc.org/articulo.oa?id=511754471023

How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative MONOGRAPH MÈTODE Science Studies Journal, 6 (2016): 161–165. University of Valencia. DOI: 10.7203/metode.6.5000 ISSN: 2174-3487. Article received: 24/03/2015, accepted: 17/06/2015.

LOOKING FOR THE ORIGIN OF LIFE IN COSMOCHEMISTRY ASTEROIDS AND THEIR CARBON-RICH METEORITES

Sandra Pizzarello

Carbonaceous chondrite meteorites are carbon-containing fragments of primitive asteroids that have offered the only samples available to date giving insights into chemical in laboratory analyses. Their study has revealed that abundant organic came to be in the ahead of terrestrial life and, by the input of these meteorites and , might have aided in the origin of our planet’s .

Keywords: biogenic elements, carbonaceous meteorites, chemical evolution, , chembiogenesis.

Louis Lerman (2010) recently wrote: and subsequent generation of , evolved through Origin problems are the most conjectural and qualitative a long cosmic history into increasingly complex of scientific questions. It is hardly surprising then that abiotic , some of which eventually reached the origin of life, like the origin of the , lacks planetary systems such as our own and may have led uniquely defining quantitative assumptions and initial to life’s precursor molecules. conditions. Individually, they are Fermi questions of a functional sort, requiring the use of a first-principles n THE CONCEPT OF CHEMBIOGENESIS conceptual approach to a situation of fundamental quantitative ignorance. That a natural pre-biotic chemical evolution could Well put, if not sobering, since reach early , an idea also cleverly referred the processes that led to the to as chembiogenesis by Von origin of life remains utterly Kiedrowski (2005), has found unknown as well as difficult to direct experimental scrutiny «THAT A NATURAL PRE- decipher. in the laboratory through the Nevertheless, the study BIOTIC CHEMICAL EVOLUTION analyses of a group of meteorites of origins have proceeded COULD REACH EARLY containing abundant organic undaunted, and that intimidating EARTH HAS FOUND DIRECT carbon, the carbonaceous ignorance has been somewhat EXPERIMENTAL SCRUTINY IN chondrites. On the basis of tempered by sharing it among these findings and the above- THE LABORATORY THROUGH a wide range of research mentioned consortium of studies, fields, such as , THE ANALYSES OF A GROUP in 1985, NASA had already cosmochemistry, and OF METEORITES CONTAINING published (Wood & Chang, evolutionary , just to name ABUNDANT ORGANIC 1985) the eye-catching summary cartoon shown in Figure 1, a few. This wide perspective has CARBON» inquired beyond life’s origin and which takes us through an brought to current understanding evolutionary cosmic path of that biological evolution, through almost ten billion years (and which all derive from a minimal and where, admittedly, the addition of a DNA strand common ancestor, was itself preceded by chemical might have been a stretch). evolution. By this process, the biogenic elements Some background may be useful: a is H, C, N, O, P, and S originating from the any small, solid body reaching the Earth from outer

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Rebeca Plana. Something happens, 2014. Mixed technique on linen, 150 × 200 cm. MONOGRAPH On the origin of life

Compound Class Structure Example No. species

Carboxylic H3COOH – C acetic 48

NH 2 – Amino acids H C – C – COOH 74 3 H

OH–

Hydroxy acids H C – C – COOH lactic acid 20 3 H

O– – Ketoacids pyruvic acid 12 H3C – C – COOH

Dicarboxylic acids succinic acid 17 HOOC – (CH2)2 – COOH

OH– OH–

Sugar alcohols & acids H CHO – C – C glyceraldehyde 19 2 H

O– –

Aldehydes & Ketones 18 H3C – C – H

Amines & Amides H3CH – C 2NH2 13

C O O H Pyridine carboxylic nicotinic acid 7 acids N

NH2 N N 5 N N H

Hydrocarbons:

Aliphatic H3CH – C 2 – CH 3 propane 140

Aromatic 87

Polar isoquinolines 14 N

Table 1. Summary of the most important molecule types in carbonaceous chondrites.

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space, for example, meteorite samples originating from the Moon, , and even Mercury have all been collected. However, their largest input comes from the Asteroid belt. Asteroids are small rocky bodies that, while falling into an orbit during the early stages of Solar System’s formation, came under the strong gravitational tug of the already formed giant planets, never succeeded in making a planet of their own and remained, in their thousands, orbiting the as aggregates of rocks between Mars and Jupiter. All meteorites reach the Earth following some disruptive impact that destabilizes their original location, but the Asteroid Belt is so crowded that collisions are also very frequent and have put asteroid fragments into Earth’s orbit since the accretion of the planet. Carbonaceous chondrites have a primitive composition and display solar-like elemental distributions depleted only, and to a limited degree, of the most volatile elements H, C, O, and N. These meteorites are rare and comprise only 4.7 % of total falls since 1806; many more are found (which, in fact, are called «finds») but, with the exception of some collected in Antarctica, they usually become quickly contaminated by the chemistry of the and,

since bacteria in particular like them as food, they Reproduced with permission from Wood and Chang (1985). eventually decompose in terrestrial environments. Figure 1. In 1985, NASA published this eye-catching infographic Carbonaceous chondrites are classified in several cartoon that takes us through an evolutionary cosmic path of subgroups on the basis, inter alia, of content, almost ten billion years (and where, admittedly, the addition of a hydrous phases within their minerals, and inclusion DNA strand might have been a stretch). differences (Zolensky et al., 1997). All carbonaceous chondrites however, free compounds contain organic carbon, ranging in can be also released from the «STUDIES OF THESE complexity from macromolecular insoluble organic materials, under insoluble organic materials METEORITES OFFER hydrothermal conditions (300 ˚C similar to terrestrial NOT ONLY PROOF THAT and 100 Megapascal) not dissimilar to simple soluble compounds, COMPOUNDS IDENTICAL TO from those found in terrestrial deep several of which are identical to LIFE’S MOLECULES FORMED vents (Yabuta, Williams, . Therefore studies Cody, Alexander, & Pizzarello, ABIOTICALLY, BUT ALSO of these meteorites offer not only 2007). This treatment may produce proof that compounds identical to INSIGHTS INTO THE ORGANIC suites of hydrocarbons as well life’s molecules formed abiotically, INVENTORY THAT WAS as -containing molecules but also insights into the organic LIKELY ACCRETED BY THE such as dicarboxylic acids and, inventory that was likely accreted EARLY EARTH» most surprisingly, large amounts by the early Earth. Table 1 of (Pizzarrelo & Groy, gives an overview of the major 2011). molecular species of compounds In spite of the extensive found in carbonaceous chondrites and their distribution, molecular and isotopic studies conducted over forty but many more are known to be present, if only by their years that have contributed greatly to our knowledge elemental composition (Schmitt-Kopplin et al., 2010). of the distribution, properties, and likely conditions The compounds listed in Table 1 (Pizzarello, Cooper, for the formation of meteoritic organic compounds, a & Flynn, 2006; Pizzarello, Williams, Lehman, Holland, comprehensive understanding of the synthetic pathways & Yarger, 2011) are usually found after extraction and even their basic origin environment (i.e., pre-solar of powders from meteorites with water and ; vs. solar) is still not fully known for some of them.

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n BIOCHEMISTRY FROM METEORITES? CHIRALITY CHIRALITY a Another theme in chembiogenesis is the study of whether any of the chemical traits of terrestrial biochemistry could derive from cosmochemistry. In the search for a possible relationship between meteorite organics and biochemistry, molecular asymmetry b stands out. Chirality, from the Greek ceir for hand, is a general property of objects that, like the hands, can exist in two forms that are mirror images of each other 1 1 M but are non-superimposable. This is also a property of I any organic molecule with a carbon and four different R R , known as an asymmetric carbon (C* in O Figure 2). The two mirror image forms of a chiral R 2 2 compound are referred to as enantiomers and, in the 4 4 case of biochemical compounds such as amino acids 3 3 c and hydroxy acids, they are referred to as D- and L- enantiomers (from Latin dexter and laevus). Chirality is first and foremost an interactive property, CHO CHO as can easily be visualized by thinking of two people

–– –– shaking their right hands rather than their right and left H –– C * ––OH H O –– C * ––H ones. On this basis, it is fundamental accumulation of –– –– CH OH CH OH life’s structures and functions; for example, all amino 2 2 acids in terrestrial have the L-configuration d while the sugar of information , DNA and RNA, is always a D-enantiomer. Chirality, therefore, Figure 2. Chirality is a general property of objects that can exist in two forms that are mirror images of each other but are non- is an indispensable molecular trait of some essential superimposable. It may be the property of assemblages of various biomolecules. components (a), (b) and any organic molecule with a carbon Given the stochastic distributions determined for all and four different substituents, referred to as an asymmetric meteorite organics, it was unexpected and quite exciting carbon (c-d). when some amino acids in meteorites were found to have an excess of L-enantiomers. At first this research Even more elusive is the assessment of a possible was controversial because of the «» exobiology, i.e., how the exogenous input of meteoritic of terrestrial proteins and the ease of terrestrial materials might have led to the origins of life. As Figure , but they were eventually detected for 1 and Table 1 suggest, the formation of molecules some compounds that are abundant in meteorites but composed of C, H, O, and N appears to be a universal not common in terrestrial biochemistry, the a-methyl- evolutionary process that leads to large chemical a-amino acids, and excesses of enantiomeric (ee) were complexity, but this occurs in fundamentally distinct observed that, even though they were not as extensive, ways before and after the onset of life. Prebiotic had the same configuration (L-) as terrestrial amino evolution, in fact, shows traits of a chemistry governed acids (Pizzarello & Groy, 2011). To date, ten of these solely by physicochemical forces while extant terrestrial compounds and one hydroxy acid have shown to be ee life, be it simple or complex, demonstrates a strict and the findings have raised anew the speculations that chemical selectivity in the structure and extraterrestrial prebiotic processes might have provided of its polymeric as well as monomeric constituents. the early Earth with a «primordial» inventory of Comparative examples can be found throughout essential organic molecules, giving biochemistry, for example, meteoritic amino acids a push due to their chiral asymmetry, i.e., this has have almost complete structural diversity for a given brought about speculation about possible exobiology. carbon number, showing decreasing abundances with Among the possible effects of the exogenous delivery the lengthening of their carbon chains, and nearly one of carbonaceous material, the extraction of vesicle hundred different ones can be found, while terrestrial forming molecules from the proteins only contain 22 components (Pizzarello, may also be of particular significance (Figure 3). In Cooper, & Flynn, 2006). 1985 Deamer demonstrated that boundary structures

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1,000th candidate and that six of the newly confirmed are near-Earth-sized and found in their host ’s habitable zones… Galileo may not have been thinking of exobiology in stating that astra regunt, but despite this, looking at the stars may still provide us with basic information after all.

REFERENCES Deamer, D. (1985). Boundary structures are formed by organic components of the Murchison . , 317, 792–794. doi: 10.1038/317792a0 Lerman, L. (2010). The primordial bubble: Water, breaking, and the origin of life. In R. M. Lyndell-Bell, S. C. Morris, D. Barrow, J. L.

Finney, & C. Harper. (Eds.), Water and life: The unique properties of H2O (pp. 259–290). Boca Raton: CRC Press.

ètode Pizzarello, S., Cooper, G. W., & Flynn, G. J. (2006). The nature and M distribution of the organic material in carbonaceous chondrites and Figure 3. A fragment of the Murchison Meteorite at the National interplanetary dust . In D. Lauretta, & H. Y. McSween Jr (Eds.), Museum of Natural History in Washington (USA). The discoveries Meteorites and the Early Solar System II (pp. 625–651). Tucson: University of Arizona Press. that this meteorite provided allowed scientists to propose that Pizzarello, S., & Groy, T. L. (2011). Molecular asymmetry in extraterrestrial meteoritic components could have contributed to the self- : An analytical perspective. Geochimica et assembly capabilities of the early Earth milieu. Cosmochimica Acta, 75, 645–656. doi: 10.1016/j.gca.2010.10.025 Pizzarello, S., Williams, L. B., Lehman, J., Holland, G. P., & Yarger, J. L. (2011). are formed from organic Abundant ammonia in primitive asteroids components extracted from «THE DATA AVAILABLE SO and the case for a possible exobiology. the Murchison meteorite, such Proceedings of the National Academy of FAR CERTAINLY ALLOWS , 108, 4303–4306. doi: 10.1073/ as a mixture of amphiphilic pnas.1014961108 US TO DRAW A PLAUSIBLE components and longer chain Schmitt-Kopplin, P., Gabelica, Z., Gougeon, carboxylic acids among others, SCENARIO, WHERE R. D., Fekete, A., Kanawati, B., Harir, M., … Hertkorn, N. (2010). High molecular which efficiently collaborate EXOGENOUS MATERIALS diversity of extraterrestrial organic in in water solutions to give a SUCH AS THOSE OF Murchison meteorite revealed 40 years after sustained increase in the its fall. Proceedings of the National Academy METEORITES AND, LIKELY, of Sciences, 107, 2763–2768. doi: 10.1073/ tension toward the formation pnas.0912157107 COMETS WERE ABUNDANTLY of membranes and vesicles Von Kiedrowski, G. (Org.). (2005, September (Deamer, 1985). These findings DELIVERED TO THE EARLY 28–October 1). Chembiogenesis: Prebiotic chemistry and early evolution. ECLT: Venice raise the interesting prospect that EARTH AND CONTRIBUTED International University. Retrieved from meteoritic components could have TO THE PLANET’S ORGANIC http://www.istpace.org/Web_Final_Report/ contributed to the self-assembly scientific_meetings_at_eclt/workshops/ POOL» second_year_april_2005_marc/prebiotic_ capabilities of the early Earth chemistry_and_ear.html milieu. Wood, J. A., & Chang, S. (Eds.). (1985). The To conclude this short overview cosmic history of the biogenic elements and compounds. Washington, DC: Scientific and Technical Information Branch, of the chemistry of carbonaceous meteorites, we could National Aeronautics and Space Administration Publisher. ask whether the title of the article is reasonable and Yabuta, H., Williams, L. B., Cody, G. D., Alexander, C. M. O’D., & Pizzarello, we can, indeed, come to think that cosmochemistry S. (2007). The insoluble carbonaceous material of CM chondrites: A possible source of discrete organic compounds under hydrothermal contributed to life’s origin. If constrained by the many conditions. & , 42, 37–48. doi: 10.1111/j.1945- unknowns that surround this origin, the data available 5100.2007.tb00216.x so far certainly allows us to at least draw a plausible Zolensky, M. E., Mittlefehldt, D. W., Lipschutz, M. E., Wang, M.-S., Clayton, R. N., Mayeda, T. K., … Barber, D. (1997). CM chondrites exhibit the scenario, where exogenous materials such as those complete petrologic range from type 2 to 1. Geochimica et Cosmochimica of meteorites and, likely, comets were abundantly Acta, 61, 5099–5115. doi: 10.1016/S0016-7037(97)00357-8 delivered to the early Earth, contributed to the planet’s organic pool, provided incipient means of selection . Professor and Research Professor at the Department of Chemistry and Biochemistry of the Arizona State University (USA). Her through some of their chiral compounds and catalysts research spanning over thirty years has been devoted to the study of organic which contributed to prebiotic molecular evolution. materials in carbonaceous chondrite meteorites, with an emphasis on the Given the large and overwhelming unknowns of this molecular, isotopic, and chiral characterization of their soluble compounds. More recently, she has focused on the study of non-racemic amino acids quest, it has been somewhat reassuring to find that, by from meteorites. She has published in journals including Science and PNAS, 6 January 2015, the Kepler mission had confirmed the among others.

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