Here's the abstract of the PNAS article ...
The coincidence of the Late Heavy Bombardment (LHB) period and the emergence of terrestrial life about 4 billion years ago suggest that extraterrestrial impacts could contribute to the synthesis of the building blocks of the first life-giving molecules. We simulated the high-energy synthesis of nucleobases from formamide during the impact of an extraterrestrial body. A high-power laser has been used to induce the dielectric breakdown of the plasma produced by the impact. The results demonstrate that the initial dissociation of the formamide molecule could produce a large amount of highly reactive CN and NH radicals, which could further react with formamide to produce adenine, guanine, cytosine, and uracil. Based on GC-MS, high-resolution FTIR spectroscopic results, as well as theoretical calculations, we present a comprehensive mechanistic model, which accounts for all steps taking place in the studied impact chemistry. Our findings thus demonstrate that extraterrestrial impacts, which were one order of magnitude more abundant during the LHB period than before and after, could not only destroy the existing ancient life forms, but could also contribute to the creation of biogenic molecules.In case you don't appreciate the significance of this research, PNAS provides you with a brief summary ...
This paper addresses one of the central problems of the origin of life research, i.e., the scenario suggesting extraterrestrial impact as the source of biogenic molecules. Likewise, the results might be relevant in the search of biogenic molecules in the universe. The work is therefore highly actual and interdisciplinary. It could be interesting for a very broad readership, from physical and organic chemists to synthetic biologists and specialists in astrobiology.The problem with all these studies is that they don't answer the most important question; what happens next?
Let's assume that the four bases were created in the atmosphere as meteorites crashed into Earth four billion years ago. Let's assume there was water in the form of early oceans or big lakes. Then what happens? Do these researchers imagine that the concentrations of these bases built up gradually over thousands of years until there were spontaneous reactions with five-carbon sugars and phosphate to form nucleotides? Then did these nucleotides assemble into short RNA molecules?
It's a very large step from demonstrating that RNA bases can be made from formamide under extreme conditions to showing that their concentrations could have been high enough to make RNA spontaneously.
We need to demand more of these researchers. If they are going to postulate that life arose in a primordial soup then it's no longer sufficient to publish one more paper on how you can make organic molecules from inorganic precursors. Enough already. That's the easy part of the hypothesis. Let's see some evidence for the hard part.
Ferus, M., Nesvorný, D., Šponer, J., Kubelík, P., Michalčíková, R., Shestivská, V., Šponer, J.E., and Civiš, S. (2014) "High-energy chemistry of formamide: A unified mechanism of nucleobase formation." Proceedings of the National Academy of Sciences Published online before print December 8, 2014. [doi: 10.1073/pnas.1412072111]