Impact synthesis of the RNA bases.

Any discussion related to how life began on this planet inevitably invokes the question as to the origin of bio-organic molecules, a field called prebiotic chemistry (1). How did organic compounds come to populate the early Earth? Before 1953, this question itself was not widely considered within the realm of experimental science. However, since the pioneering results of the Miller–Urey experiment that produced amino acids from electrical discharges passing through simple gases (2), the field of prebiotic chemistry has been extremely prodigious in demonstrating abiotic syntheses for multitudes of organic compounds. However, it became apparent that prebiotic chemistry was faced with a more challenging question. How did the biomolecules of life get selected out of such complex, prebiotic mixtures? Particular significance has been placed on understanding the selection of the nucleobases adenine (A), cytosine (C), guanine (G), and uracil (U), given their role in the RNA world hypothesis (3). The hypothesis is a premise that life may have emerged with genetic and enzymatic function based exclusively on RNA (4). Some research has pointed to the possibility that selection criteria may have relied on nucleobases that were able to persist the longest in the prebiotic environment. Others have considered the possibility that early RNA life used a wide range of nucleobases, and over time unique selection pressures emerged that favored the extant bases. In terms of using a synthetic origin or availability argument, it has been found that varying conditions are needed to demonstrate the production of all of the RNA bases. Invoking multiple stage and multiple environmental scenarios for the selective prebiotic synthesis of the nucleobases seems extremely unlikely. What would be intriguing would be the demonstration that all of the RNA bases are selectively produced under the same conditions, and that those conditions might be considered plausible to prebiotic chemistry and the early Earth environment. This is what Ferus et al. set out to do in their most recent contribution, and they begin with a simple organic compound called formamide (Fig. 1) (5). Formamide appears to be widespread in the universe. Astronomers have recently reported its presence in our solar system found within the atmospheres of comets (6), and since the 1970s, formamide has been detected in multiple regions in the interstellar medium (7). The known chemistry and ubiquity of formamide has made it an attractive primordial feedstock compound for the production of many prebiotic molecules (8). Experiments on the prebiotic synthesis of nucleobases using formamide have