Path 8: PAH World (Polycyclic Aromatic Hydrocarbons as Scaffolds)

Rationale: Before RNA, flat ring molecules like PAHs (abundant carbon compounds in space, analogous to graphite sheets) formed matrices that helped assemble the first informational polymers. PAHs tend to stack in water, forming sheet-like aggregates with a spacing (~0.34 nm) nearly identical to the spacing of nucleobases in DNA/RNA stacks. This coincidence suggests that PAHs could have templated the arrangement of bases, encouraging nucleotides to line up and polymerize along the PAH surface. PAHs are amphiphilic (one face can be hydrophobic, especially if partially oxidized to poly-alcohols), so they could also help form pseudo-membranes or micelles. The hypothesis (proposed by S. Platts in 2005) posits a “PAH world” that preceded the RNA world: UV-irradiated PAHs in ponds or on dust would get functionalized (adding -OH etc.) making them more soluble. These modified PAHs could then stack and bind flat heterocyclic molecules (the bases) by π–π interactions, arranging them for polymerization.

Prerequisites: Organic chemistry of PAHs, understanding how they interact with nucleic acids and lipids. Some familiarity with astrochemistry – PAHs are found in meteorites and interstellar clouds, so they likely rained down on early Earth.

Dependencies: The PAH world is a supporting player – it still needs actual genetic polymers to emerge. Think of it as a facilitator for Path 4 (RNA world) – thus it depends on the chemistry of cyanide, formaldehyde, etc., to make those bases and sugars which PAHs would then assemble. It also connects to Path 3 (since PAHs are abundant in space, panspermia could deliver them).

Signs of Progress: Experiments showing that bases or nucleotide analogues adsorb preferentially onto PAH layers (some studies indicate that purines and pyrimidines do stack onto PAH surfaces in water). Another promising result: certain PAHs, when exposed to UV in simulated early Earth conditions, yield amphiphilic molecules that spontaneously form membranous vesicles – thus PAHs might simultaneously assist in compartment formation. If research demonstrates a PAH-assisted polymerization of nucleotides (e.g. an RNA chain growing along a PAH template), that would strongly support this idea.

Base Camps

The original Deep Research document notes that detailed Base Camps for Path 8 “would follow similarly” to the first six paths (covering organic cosmochemistry and how planar molecules might scaffold assembly) but were not fully enumerated in the source text due to length. The Inventory above provides the essential rationale and research directions.

Bibliography

(No separate path bibliography was provided for Path 8 in the source text; see the Hub page for cross-cutting references and the Partial Results section for relevant experimental findings.)