One of the most significant problems in origins of life scenarios is that the most common molecules that compose gases, liquids or solids found on our planet, or around most solar systems, simply don’t interact with one another to synthesize organic molecules under common circumstances. Even worse, molecules that co-occur with one another tend not to even be efficient pairings of electron donors and acceptors, basically because of the second law of thermodynamics: on long time scales, systems that can approach equilibrium tend to do so. For this reason, an aggregate search strategy of ‘Follow the Water’ combined with ‘Follow the Energy’ has been proposed to locate specific settings where sizeable energy gradients put electron donors, electron acceptors, and sources of carbon and phosphorus all in close proximity to one another. The problem is that getting them all in the same place, at the same time, is a major challenge.
Radicals offer one possible solution to this challenge: under radiolytic conditions, common molecules are broken into fragments that are extremely reactive. Not just any particular compounds, but nearly any compound. Water itself, H2O, generates over a half-dozen powerful electron donors and acceptors. Table salt, NaCl, generates a modest array of very reactive species upon interaction with water radicals that . And even N2, one of the most strongly-bonded and least reactive molecules, becomes a ready source of atomic nitrogen in excited states that can generate an array of reactive nitrogenous species in different redox states. Note that this broad foundation for energy transfer can form in the absence of carbon, but all of these species can and do shape organic synthesis.
There is a consistent theme across all of these examples: it is that the common immediately becomes uncommon, the inert becomes powerful, after only a single bond cleavage event. This is more than just an experimental convenience. It means that a system can be completely enclosed in terms of mass, and still lead to complex outcomes with powerful chemosynthetic potential. A completely enclosed system removes the need to precisely introduce powerful reactants, in appropriate proportions, and to remove specific waste or side products. In terms of experimental design, it means that systems that model life’s origins do not require building and maintaining a chemostat, and can function ‘hands-off’ and completely free of human intervention.