  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 $330 \pm250$ ppb and $16 \pm13$ 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.
