Carbonaceous Chondrite Meteorites: the Chronicle of a Potential Evolutionary Path between Stars and Life.

The biogenic elements, H, C, N, O, P and S, have a long cosmic history, whose evolution can still be observed in diverse locales of the known universe, from interstellar clouds of gas and dust, to pre-stellar cores, nebulas, protoplanetary discs, planets and planetesimals. The best analytical window into this cosmochemical evolution as it neared Earth has been provided so far by the small bodies of the Solar System, some of which were not significantly altered by the high gravitational pressures and temperatures that accompanied the formation of larger planets and may carry a pristine record of early nebular chemistry. Asteroids have delivered such records, as their fragments reach the Earth frequently and become available for laboratory analyses.

Molecular Asymmetry in Prebiotic Chemistry: An Account from Meteorites.

Carbonaceous Chondrite (CC) meteorites are fragments of asteroids, solar planetesimals that never became large enough to separate matter by their density, like terrestrial planets. CC contains various amounts of organic carbon and carry a record of chemical evolution as it came to be in the Solar System, at the time the Earth was formed and before the origins of life. We review this record as it pertains to the chiral asymmetry determined for several organic compounds in CC, which reaches a broad molecular distribution and enantiomeric excesses of up to 50%-60%.

Processing of meteoritic organic materials as a possible analog of early molecular evolution in planetary environments.

The composition of the Sutter's Mill meteorite insoluble organic material was studied both in toto by solid-state NMR spectroscopy of the powders and by gas chromatography-mass spectrometry analyses of compounds released upon their hydrothermal treatment. Results were compared with those obtained for other meteorites of diverse classifications (Murray, GRA 95229, Murchison, Orgueil, and Tagish Lake) and found to be so far unique in regard to the molecular species released. These include, in addition to O-containing aromatic compounds, complex polyether- and ester-containing alkyl molecules of prebiotic appeal and never detected in meteorites before.

Radar-enabled recovery of the Sutter's Mill meteorite, a carbonaceous chondrite regolith breccia.

Doppler weather radar imaging enabled the rapid recovery of the Sutter's Mill meteorite after a rare 4-kiloton of TNT-equivalent asteroid impact over the foothills of the Sierra Nevada in northern California. The recovered meteorites survived a record high-speed entry of 28.6 kilometers per second from an orbit close to that of Jupiter-family comets (Tisserand's parameter = 2.

Large enantiomeric excesses in primitive meteorites and the diverse effects of water in cosmochemical evolution.

Carbonaceous chondrites are meteoritic fragments of asteroids that avoided the geological reprocessing of larger planets and allow laboratory probing of early solar-nebula materials. Among these, Renazzo-type (CR) chondrites found in Antarctica appear remarkably pristine and are distinguished by abundant organic materials and water-soluble molecules such as amino acids and ammonia. We present a comprehensive analysis of the organic composition of selected CR meteorites of different petrographic classification and compare compounds' abundance and distribution as they may relate to asteroidal aqueous processing and concomitant evolution of the mineral phases.

Abundant ammonia in primitive asteroids and the case for a possible exobiology.

Carbonaceous chondrites are asteroidal meteorites that contain abundant organic materials. Given that meteorites and comets have reached the Earth since it formed, it has been proposed that the exogenous influx from these bodies provided the organic inventories necessary for the emergence of life. The carbonaceous meteorites of the Renazzo-type family (CR) have recently revealed a composition that is particularly enriched in small soluble organic molecules, such as the amino acids glycine and alanine, which could support this possibility.

The organic composition of carbonaceous meteorites: the evolutionary story ahead of biochemistry.

Carbon-containing meteorites provide a natural sample of the extraterrestrial organic chemistry that occurred in the solar system ahead of life's origin on the Earth. Analyses of 40 years have shown the organic content of these meteorites to be materials as diverse as kerogen-like macromolecules and simpler soluble compounds such as amino acids and polyols. Many meteoritic molecules have identical counterpart in the biosphere and, in a primitive group of meteorites, represent the majority of their carbon.

Stereoselective syntheses of pentose sugars under realistic prebiotic conditions.

Glycolaldehyde and DL-glyceraldehyde reacted in a water-buffered solution under mildly acidic conditions and in the presence of chiral dipeptide catalysts produced pentose sugars whose configuration is affected by the chirality of the catalyst. The chiral effect was found to vary between catalysts and to be largest for di-valine. Lyxose, arabinose, ribose and xylose are formed in different amounts, whose relative proportions do not change significantly with the varying of conditions.

Molecular asymmetry in extraterrestrial chemistry: Insights from a pristine meteorite.

The nonracemic amino acids of meteorites provide the only natural example of molecular asymmetry measured so far outside the biosphere. Because extant life depends on chiral homogeneity for the structure and function of biopolymers, the study of these meteoritic compounds may offer insights into the establishment of prebiotic attributes in chemical evolution as well as the origin of terrestrial homochirality. However, all efforts to understand the origin, distribution, and scope of these amino acids' enantiomeric excesses (ee) have been frustrated by the ready exposure of meteorites to terrestrial contaminants and the ubiquitous homochirality of such contamination.

Question 2: why astrobiology?

Astrobiological studies of abiotic organic chemistry, such as it is observed in interstellar molecular clouds or found in comets and meteorites, offer a glimpse of the chemical evolution that preceded the onset of life. They also allow to evaluate the possibility that the molecules produced through the long cosmic history of the biogenic elements contributed to the early Earth organic pool and facilitated prebiotic molecular evolution.

The chemistry that preceded life's origin: a study guide from meteorites.

Carbonaceous meteorites are rare fragments of asteroids that contain organic carbon of diverse composition, various complexity, and whose lineage can in several instances be traced back to pre-solar environments. Their analyses offer a unique glimpse into the chemistry of the solar system that preceded life and may have been available to its emergence on the early Earth. While the heterogeneity of the organic materials of meteorites is indicative of random synthetic processes for their formation, some of their components have identical counterparts in the biosphere, and a group of meteoritic amino acids were found to display chiral asymmetry, a property known since the time of Pasteur to be inextricably linked to life's processes.

The peptide-catalyzed stereospecific synthesis of tetroses: a possible model for prebiotic molecular evolution.

Using a water-based prebiotic model of sugar synthesis involving glycolaldehyde self-condensation, we demonstrate that homochiral L-dipeptide catalysts lead to the stereospecific syntheses of tetroses. The asymmetric effect is largest for erythrose, which may reach a D-enantiomeric excess of >80% with L-Val-L-Val catalyst. Based on results obtained with various peptides, we propose a possible catalytic-reaction intermediate, consisting of an imidazolidinone ring formed between the two nitrogen atoms of the peptide catalyst and the C1 of one glycolaldehyde molecule.

The chemistry of life's origin: a carbonaceous meteorite perspective.

Carbonaceous chondrite meteorites are primitive asteroidal fragments that contain organic carbon and offer a glimpse of the abiotic chemical processes that preceded the onset of life. Their organic material displays structures as diverse as kerogen-like macromolecules and simpler soluble compounds that range from polar amino acids and polyols to nonpolar hydrocarbons. Several of these compounds have identical counterparts in terrestrial biomolecules and some of the amino acids show a unique l-asymmetry, suggesting their possible contribution to terrestrial molecular evolution and the origin of biological homochirality.

Chemical evolution and meteorites: an update.

Carbonaceous chondrites are a primitive group of meteorites, which contain abundant organic material and provide a unique natural record of prebiotic chemical evolution. This material comprises a varied suite of soluble organic compounds that are similar, sometimes identical, to those found in the biosphere, such as amino acids, carboxylic acids, and sugar derivatives. Some amino acids of this suite also show L-enantiomeric excesses, and suggest the possibility they may have contributed to terrestrial homochirality by direct input of meteoritic material to the early Earth.