PAH world hypothesis

The PAH world hypothesis is a speculative hypothesis that proposes that polycyclic aromatic hydrocarbons (PAHs), known to be abundant in the universe,[1][2][3] including in comets,[4] and assumed to be abundant in the primordial soup of the early Earth, played a major role in the origin of life by mediating the synthesis of RNA molecules, leading into the RNA world.

[5] The 1952 Miller–Urey experiment demonstrated the synthesis of organic compounds, such as amino acids, formaldehyde and sugars, from the original inorganic precursors the researchers presumed to have been present in the primordial soup (but is no longer considered likely).

[8] A more thoroughly elaborated idea has been published by Ehrenfreund et al.[9] Polycyclic aromatic hydrocarbons are the most common and abundant of the known polyatomic molecules in the visible universe, and are considered a likely constituent of the primordial sea.

"[13]) PAHs, subjected to interstellar medium (ISM) conditions, are transformed, through hydrogenation, oxygenation and hydroxylation, to more complex organics — "a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively".

When in solution, they assemble in discotic mesogenic (liquid crystal) stacks which, like lipids, tend to organize with their hydrophobic parts protected.

Therefore, it encourages preferential attachment of flat molecules such as pyrimidine and purine nucleobases, the key constituents (and information carriers) of RNA and DNA.

The formaldehyde oligomers would eventually be replaced with more stable ribose-phosphate molecules for the backbone material, resulting in a starting milestone for the RNA world hypothesis, which speculates about further evolutionary developments from that point.