Many type localities have been proposed as possible prebiotic settings, and many imaginative theories and hypotheses have been developed to design studies that link these settings to the production of cellular compounds. The theories that have motivated these different studies have greatly advanced the field of prebiotic chemistry, but they have also outlined some serious chemosynthetic obstacles to life’s origins. Currently, one of the dominant theories for life’s origins is the concept of RNA World, but it also necessitates the co-synthesis of a diverse variety of compounds (sugars, nucleobases, reactive phosphates, etc.). A historically dominant theory has been the concept of pyrite catalysis, which has been correlated with settings such as hydrothermal vents and a geochemical process called serpentinization, but to date there has been no compelling demonstration that the electron potential between H2 and CO2 can generate carbon-bearing compounds other than CH4 in any significant amount. 

Radical chemistry affords many unique chemical and physical mechanisms and pathways that can link a wide variety of geochemical, cosmochemical and atmospheric starting compounds to organic synthesis. There are so many possibilities, and so little data, that one of the main challenges that REPO faces is prioritizing which known or theorized pathways (with specific regard to prebiotic synthesis) ought to be studied first. 

In this section, we track hypotheses that have been developed to apply radical chemistry to exploring life’s origins. The hypotheses are arranged hierarchically and in general subject areas. The ordering of the general subject areas is not significant. However, as general hypotheses have been corroborated, the next levels of more specific hypotheses that are built directly upon the corroboration of the more general hypothesis are denoted with appended numbers. 

Section 1: Radical-driven organic synthesis pathways

1.0 Radicals can generate prebiotically relevant compounds 
Status: Corroborated and under refinement (Negron-Mendoza, Draganic).

1.1 Radicals can simultaneously generate different prebiotically-relevant compounds 
Status: Under investigation (Negron-Mendoza, Dondi, Adam, Fahrenbach, Yi).

1.1.1 Radicals can generate sugars 
Status: Under investigation (Yi, Fahrenbach, Adam).

1.1.2 Radicals can generate nucleobases 
Status: Under investigation (Adam).

1.1.3 Radicals can generate reactive phosphates 
Status: Under investigation (Adam, Lago).

1.1.4 Radicals can generate condensing agents and leaving agents
Status: Under investigation (Fahrenbach, Yi). 

1.1.5 Radicals can generate thiosulfates 
Status: Proposed but not under investigation (Adam, Kacar, Fahrenbach, Yi). 

1.1.6 Radicals can generate phospholipids or other primitive membrane compounds
Status: Proposed but not under investigation. 

Section 2: Radicals and dynamic compartmentalization

2.0 Radicals can power complex, responsive vesicle formation.
Status: Corroborated and under refinement (Perez-Mercader, Duenas)

2.0.1 [RAFT+PISA] systems can function under a broader array of laboratory conditions and with a wider variety of substrates. 
Status: Under investigation (Perez-Mercader, Duenas). 

2.0.2 [RAFT+PISA] system analogs can work under geochemically plausible conditions. 
Status: Proposed but not under investigation. 

Section 3: Radical network topology and systems chemistry

3.0 Radical network topologies can bear resemblance to complex biological network topologies. 
Status: Corroborated and under refinement (Adam et al., 2021). 

3.0.1 Complex biological networks and resultant dynamic behaviors are positively correlated with connectivity heterogeneity (i.e., heavy-tailed distributions)
Status: Corroborated and under refinement (Barabassi, Jeong)

3.0.1.1 Complex biological networks and resultant dynamic behaviors are contingent upon a specific heavy-tailed distribution class (e.g., power law, lognormal, lognormal with exponential truncation, etc.) 
Status: Under investigation (Lima-Mendez and van Helden, 2009)

3.0.1.2 Radical chemical reaction network heavy-tailed connectivity distributions are positively correlated with the chemical and physical properties of specific radical species
Status: Corroborated and under refinement (Adam et al., 2021)

3.0.1.2.1 Radical chemical reaction network connectivity distributions are positively correlated with incomplete knowledge of chemical reaction intermediates
Status: Under investigation. 

3.0.1.2.2 Radical chemical reaction network connectivity distributions are positively correlated with observational bias (i.e., analytical technique capabilities or limitations)
Status: Under investigation. 

3.0.1.2.3 Radical chemical reaction network connectivity distributions are positively correlated with experimental design bias (i.e., disproportionate effects of subject area disciplinary attention or funding)
Status: Under investigation. 

3.0.1.2.4 Radical chemical reaction network connectivity distributions are positively correlated with radical species kinetic barriers, reactive promiscuity, stability, or electron potentials. 
Status: Under investigation. 

3.1 Autocatalytic cycles can be formed de novo by radicals. 
Status: Under investigation. 

3.1.1 Network simple cycle density is positively correlated with autocatalytic cycle occurrence. 
Status: Under investigation. 

3.1.2 Network connectivity heterogeneity (i.e., heavy-tailed distribution) is positively correlated with autocatalytic cycle occurrence. 
Status: Under investigation. 

3.2 The aggregate radical-driven chemical reaction network described in Adam et al. (2021) can be realized in a single pot experimental system. 
Status: Under investigation.

3.3 Radical-catalyzed chemistry under gamma- and x-ray photon irradiation conditions can de novo generate, support and spinoff metal-catalyzed chemical subnetworks under UV- and visible-photon irradiation conditions. 
Status: Under investigation (Kacar, Adam). 

3.3.1 Radical-catalyzed chemical reaction networks could have preceded metal-catalyzed pathways and cycles found in metabolism. 
Status: Proposed but not currently under investigation (Adam). 

Section 4: Natural settings for radical synthesis

4.0 Complex radical-powered chemical reaction networks can occur in atmospheres
Status: Corroborated and under refinement (Zahnle, Sole, Lara, Cable, Airapetian). 

4.1 Complex radical-powered chemical reaction networks can occur in geochemical settings
Status: Corroborated and under refinement (Cockell, Draganic, Adam). 

4.2 Complex radical-powered chemical reaction networks can occur at the interface between atmospheric and geochemical reservoirs
Status: Corroborated and under refinement (Taylor and Anderson, 2010)

4.3 Complex radical-powered chemical reaction networks can occur in the cosmochemical/interstellar environment
Status: Under investigation (Adam, Sephus, Zubarev)

4.4 Complex radical-powered chemical reaction networks can occur on exoplanet types not found in our solar system
Status: Under investigation (Adam, Sephus, Zubarev)