Seeding the Pregenetic Earth: Meteoritic Abundances of Nucleobases and Potential Reaction Pathways

Abstract

Carbonaceous chondrites are a class of meteorite known for having a high content of water and organics. In this study, abundances of the nucleobases, i.e., the building blocks of RNA and DNA, found in carbonaceous chondrites are collated from a variety of published data and compared across various meteorite classes. An extensive review of abiotic chemical reactions producing nucleobases is then performed. These reactions are then reduced to a list of 15 individual reaction pathways that could potentially occur within meteorite parent bodies. The nucleobases guanine, adenine and uracil are found in carbonaceous chondrites in the amounts of 1$-$500 ppb. It is currently unknown which reaction is responsible for their synthesis within the meteorite parent bodies. One class of carbonaceous meteorites dominate the abundances of both amino acids and nucleobases$-$the so-called CM2 (e.g. Murchison meteorite). CR2 meteorites (e.g. Graves Nunataks) also dominate the abundances of amino acids, but are the least abundant in nucleobases. The abundances of total nucleobases in these two classes are $330\pm 250$ ppb and $16\pm 13$ ppb respectively. Guanine most often has the greatest abundances in carbonaceous chondrites with respect to the other nucleobases, but is 1$-$2 orders of magnitude less abundant in CM2 meteorites than glycine (the most abundant amino acid). Our survey of the reaction mechanisms for nucleobase formation suggests that Fischer-Tropsch synthesis (i.e. CO, H${}_2$ and NH${}_3$ gases reacting in the presence of a catalyst such as alumina or silica) is the most likely for conditions that characterize early states of planetesimals.

11 pages, 4 figures, accepted for publication in ApJ

References in corpus (1)

• Extraterrestrial nucleobases in the Murchison meteorite

Cited by in corpus (11)

• Origin of the RNA World: The Fate of Nucleobases in Warm Little Ponds
• Prebiotic precursors of the primordial RNA world in space: Detection of NH${}_2$OH
• Towards RNA life on Early Earth: From atmospheric HCN to biomolecule production in warm little ponds
• A Consistent Reduced Network for HCN Chemistry in Early Earth and Titan Atmospheres: Quantum Calculations of Reaction Rate Coefficients
• Meteorites and the RNA World: A Thermodynamic Model of Nucleobase Synthesis within Planetesimals
• Possible Ribose Synthesis in Carbonaceous Planetesimals
• UV resistance of nucleosides -- an experimental approach
• Meteorites and the RNA World: Synthesis of Nucleobases in Carbonaceous Planetesimals and the Role of Initial Volatile Content
• Prebiotic Vitamin B${}_3$ Synthesis in Carbonaceous Planetesimals
• SETI@home: Data Analysis and Findings
• SETI@home: Data Acquisition and Front-End Processing